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Biological Monitoring of Occupational
Exposure to Polycyclic Aromatic
Hydrocarbons in Prebake Smelting
Ross Di Corleto
Bachelor of Applied Science (Applied Chemistry)
Postgraduate Diploma Occupational Hygiene
Master of Science
A thesis submitted for the degree of Doctor of Philosophy
School of Public Health, Faculty of Health
Queensland University of Technology
2010
Keywords
• 1-hydroxypyrene
• prebake
• smelting
• biological monitoring
• benzene-soluble fraction
• coal tar pitch volatiles
• polycyclic aromatic hydrocarbons
• anode plant
• personal monitoring
ii
Abstract
In 1984, the International Agency for Research on Cancer determined that working
in the primary aluminium production process was associated with exposure to
certain polycyclic aromatic hydrocarbons (PAHs) that are probably carcinogenic to
humans. Key sources of PAH exposure within the occupational environment of a
prebake aluminium smelter are processes associated with use of coal-tar pitch.
Despite the potential for exposure via inhalation, ingestion and dermal adsorption,
to date occupational exposure limits exist only for airborne contaminants.
This study, based at a prebake aluminium smelter in Queensland, Australia,
compares exposures of workers who came in contact with PAHs from coal-tar pitch
in the smelter’s anode plant (n = 69) and cell-reconstruction area (n = 28), and a
non-production control group (n = 17). Literature relevant to PAH exposures in
industry and methods of monitoring and assessing occupational hazards associated
with these compounds are reviewed, and methods relevant to PAH exposure are
discussed in the context of the study site.
The study utilises air monitoring of PAHs to quantify exposure via the inhalation
route and biological monitoring of 1-hydroxypyrene (1-OHP) in urine of workers to
assess total body burden from all routes of entry. Exposures determined for similar
exposure groups, sampled over three years, are compared with published
occupational PAH exposure limits and/or guidelines.
Results of paired personal air monitoring samples and samples collected for 1-OHP
in urine monitoring do not correlate. Predictive ability of the benzene-soluble
fraction (BSF) in personal air monitoring in relation to the 1-OHP levels in urine is
poor (adjusted R2 < 1%) even after adjustment for potential confounders of smoking
status and use of personal protective equipment.
For static air BSF levels in the anode plant, the median was 0.023 mg/m3 (range
0.002–0.250), almost twice as high as in the cell-reconstruction area (median =
0.013 mg/m3, range 0.003–0.154). In contrast, median BSF personal exposure in the
iii
anode plant was 0.036 mg/m3 (range 0.003–0.563), significantly lower than the
median measured in the reconstruction area (0.054 mg/m3, range 0.003–0.371) (p =
0.041). The observation that median 1-OHP levels in urine were significantly higher
in the anode plant than in the reconstruction area (6.62 µmol/mol creatinine, range
0.09–33.44 and 0.17 µmol/mol creatinine, range 0.001–2.47, respectively) parallels
the static air measurements of BSF rather than the personal air monitoring results (p
< 0.001). Results of air measurements and biological monitoring show that tasks
associated with paste mixing and anode forming in the forming area of the anode
plant resulted in higher PAH exposure than tasks in the non-forming areas; median
1-OHP levels in urine from workers in the forming area (14.20 µmol/mol
creatinine, range 2.02–33.44) were almost four times higher than those obtained
from workers in the non-forming area (4.11 µmol/mol creatinine, range 0.09–26.99;
p < 0.001). Results justify use of biological monitoring as an important adjunct to
existing measures of PAH exposure in the aluminium industry. Although
monitoring of 1-OHP in urine may not be an accurate measure of biological effect
on an individual, it is a better indicator of total PAH exposure than BSF in air.
In January 2005, interim study results prompted a plant management decision to
modify control measures to reduce skin exposure. Comparison of 1-OHP in urine
from workers pre- and post-modifications showed substantial downward trends.
Exposure via the dermal route was identified as a contributor to overall dose.
Reduction in 1-OHP urine concentrations achieved by reducing skin exposure
demonstrate the importance of exposure via this alternative pathway.
Finally, control measures are recommended to ameliorate risk associated with PAH
exposure in the primary aluminium production process, and suggestions for future
research include development of methods capable of more specifically monitoring
carcinogenic constituents of PAH mixtures, such as benzo[a]pyrene.
iv
Contents
Page
1.0
INTRODUCTION
1
1.1
Background to the research
1
2
1.1.1 What are polycyclic aromatic hydrocarbons (PAHs)?
1.1.2 PAH carcinogenicity associated with aluminium smelting 4
1.2
Research contribution
1.3
Thesis outline
8
10
11
12
2.0
LITERATURE REVIEW
13
2.1
Routes of exposure
1.2.1 Aims and objectives
1.2.2 Hypotheses
2.4
2.5
2.6
2.7
Non-occupational exposures
Biological exposure index
Biological effect monitoring
Summary
14
15
16
16
20
22
23
25
28
29
30
32
34
3.0
METHODS
35
3.1
3.2
3.3
Introduction
Study context – plant process description
Exposure groups
35
36
43
47
47
48
48
49
49
49
50
50
50
51
51
52
54
2.1.1 Inhalation
2.1.2 Ingestion
2.1.3 Skin absorption
2.2
2.3
Measures of PAH biological effect
Exposure monitoring
2.3.1 Air monitoring
2.3.2 Biological monitoring
2.3.3 Exposure quantification
3.3.1 Forming group
3.3.1.1 Former technician
3.3.1.2 Tower technician
3.3.1.3 Equipment technician
3.3.2 Non-forming group
3.3.2.1 Mezzanine floor technician
3.3.2.2 Raw materials technician
3.3.2.3 Controller
3.3.2.4 Crew leader
3.3.2.5 Bake crane operator
3.3.2.6 Bake floor operator
3.3.3 Reconstruction group
3.3.3.1 Process technician
3.3.3.2 Bricklayer
v
3.3.4 Non-production group
3.3.5 Exposure profile
3.3.6 Personal protective equipment
3.4
Recruitment of study participants
3.5
Exposure monitoring
3.4.1 Sample size calculations
3.5.1 Airborne exposure monitoring
3.5.1.1 Stationary monitoring of the process
3.5.1.2 Occupational monitoring of workers
3.5.1.3 Pre-shift briefing and daily work log
3.5.1.4 Analysis of air monitoring
54
54
55
56
57
58
58
59
64
65
3.6
Data management and statistical analysis
3.6.1 Outliers
66
70
70
72
73
74
75
77
4.0
RESULTS
79
4.1
4.2
Introduction
Exposure variation in a prebake smelter (hypothesis 1)
79
81
81
81
82
3.5.2 Biological marker monitoring
3.5.2.1
3.5.2.2
3.5.2.3
3.5.2.4
Biological sample collection
Combined sampling
Potential confounders
Participant communication
4.2.1 Static exposure levels
4.2.2 Personal exposure levels
4.2.3 Biological 1-OHP levels
4.3
Exposure variation in an anode plant of a prebake smelter
(hypothesis 2)
4.3.1 Static exposure levels
4.3.2 Personal exposure levels
4.3.3 Biological 1-OHP levels
4.4
Personal air monitoring of BSF exposure and relationship to
1-OHP levels in urine (hypothesis 3)
4.4.1 Preliminary analysis ignoring potential confounders
4.4.1.1 Sensitivity of conclusion to presence of
multiple measures
4.4.1.2 Impact of outlier
4.4.2 Multiple linear regressions
4.4.2.1 Role of confounders
4.4.2.2 Adjustment for identified confounders
4.4.2.3 Skin Exposure
4.4.2.4 Potential effect modification (subgroup
differences in size of association)
4.5
Process intervention results
84
84
85
85
85
86
86
86
87
87
89
93
94
95
vi
5.0
DISCUSSION
97
5.1
Introduction
97
5.1.1 Exposures compared between the anode plant and the
cell-reconstruction area of a prebake smelter
5.1.2 Exposures compared between forming and non-forming
areas of the anode plant of a prebake smelter
5.1.3 Impact of unscheduled process interactions
5.1.4 Personal protective equipment
5.1.5 Assessment of the relationship between BSF in personal
air samples and 1-OHP in urine
5.2
5.3
5.4
5.5
5.6
Strengths and limitations
Process intervention as a result of early findings
Additional key points
Future research
Recommendations for control measures
5.6.1 Engineering
5.6.2 Administrative
5.6.3 Personal protective equipment
5.6.4 Occupational health practice
5.6.5 Monitoring
5.6.6 Site Policy
5.7
Conclusions
98
102
106
107
109
111
114
116
123
125
125
126
128
128
129
129
129
REFERENCES
131
APPENDICES
143
Appendix 1:
Appendix 2:
Appendix 3:
Appendix 4:
Appendix 5:
Appendix 6:
143
149
151
152
153
Participant recruitment presentation
Participant consent form
Participant daily work log
Participant questionnaire
Statistical analysis roadmap
Aluminium smelting protocol for coal tar pitch volatile
(CTPV) risk management.
Appendix 7: Green Carbon PPE matrix
154
162
vii
List of Tables
Page
Table 2.1:
Absorption indices of pyrene and PAH for different anatomical
sites (Adapted from van Rooij et al., 1993b)
18
Table 2.2:
Comparison of RPFs for PAHs (Willes et al., 1992)
22
Table 3.1:
Number of study participants and % participation
57
Table 3.2:
Data for power and sample size calculations for the various
SEGs
58
Average levels of PAH compounds in air monitoring in
anode plant green carbon assessed by gas chromatography
(Method 5515 in NIOSH, 1994)
69
Median static and personal measures of BSF in air and 1-OHP
in urine, by sections within a prebake smelter
81
Identification of potential confounding variables of the
association between 1-OHP levels and personal BSF levels
88
Relationship of 1-OHP levels and BSF for all samples in the
anode plant and reconstruction areas at a prebake smelter site:
impact of identified confounding variables (n = 58)
90
Table 3.3:
Table 4.1:
Table 4.2:
Table 4.3:
Table 4.4:
Relationship of 1-OHP levels and BSF in the anode plant at the
prebake smelter site: impact of identified confounding
variables (n = 39)
91
Table 4.5:
Relationship of 1-OHP levels and BSF in the anode plant
forming area at the prebake smelter site: impact of identified
confounding variables (n = 17)
92
Relationship of 1-OHP levels and BSF in the anode plant
non-forming area at the prebake smelter site: impact of
confounding variables (n = 22)
93
Table 4.6:
Table 4.7:
Relationship of 1-OHP levels and skin exposure in the anode
plant and reconstruction area at the prebake smelter site: impact
of identified confounding variables (n = 66)
94
Table 4.8:
Degree of effect modification, by work area, of the relationship
between 1-OHP levels and BSF among workers in all the
combined groups
95
Table 4.9:
1-OHP in urine post-shift minus pre-shift for green carbon
maintenance SEG sampled before and after changes
implemented in 2005
96
viii
List of Figures
Page
Figure 1.1:
PAH ring structures of naphthalene, pyrene, benzo[a]pyrene
and dibenzo[a,e]pyrene (Freeman, 2008)
3
Prebake aluminium reduction cell showing key components
including anodes and cathodes (Boyne Smelters Ltd, 2001)
6
Figure 1.3:
Relationship of SEGs studied within the prebake smelter
10
Figure 2.1:
Level of dose of UVA required for a reaction on the skin in
relation to varying lengths of skin contact time with coal-tar
pitch (Adapted from Diette et al., 1983)
19
Metabolism sequence of BaP to the bay region diol epoxide,
(+)-BaP-7,8-diol-9,10-epoxide-2 (Hodgson & Smart, 1985)
20
Different routes of exposure, distribution and metabolism of
pyrene (ACGIH, 2005)
26
Figure 1.2:
Figure 2.2:
Figure 2.3:
Figure 3.1:
Centre-break prebake smelter aluminium reduction cell as used
in the smelter in which the study was undertaken (IPAI, 1982) 38
Figure 3.2:
Side-break prebake smelter aluminium reduction cell
(IPAI, 1982)
38
Figure 3.3:
New anode being installed into a prebake cell showing a typical
configuration of a rod assembly and the carbon block which has
been spray-coated with aluminium
39
Figure 3.4:
Consumed anode being removed from a cell in a prebake
smelter reduction line
40
Figure 3.5:
Vertical-stud Söderberg aluminium reduction cell (IPAI, 1982) 41
Figure 3.6:
Horizontal-stud Söderberg aluminium reduction cell (IPAI,
1982)
41
Figure 3.7:
Vertical-stud Söderberg aluminium smelter reduction line
42
Figure 3.8:
Structure and location of the study’s exposure groups
44
Figure 3.9:
Carbon anode process within the anode plant
45
Figure 3.10:
Carbon bake crane lowering green anodes into the bake furnace
pit
51
Figure 3.11:
Mechanical ramming of paste into the joints between the carbon
blocks of the cathode using a Brochet machine
53
Figure 3.12:
Ramming of paste into side-wall join using hand rammers
53
ix
Figure 3.13:
Potential exposure levels of SEGs
55
Figure 3.14:
Clothing and PPE worn for working with coal-tar pitch paste
56
Figure 3.15:
Monitoring pump and sample train configuration for NIOSH
method 5042
60
Static sample pump setup in the green carbon paste area on the
6th floor of the anode plant
62
Carbon bake furnace for reduction lines 1 & 2; locations of
static samples
62
Carbon bake furnace for reduction line 3; locations of static
samples
62
Figure 3.19:
Cell-reconstruction site static sample locations
63
Figure 3.20:
Monitoring pump and sample train configuration with XAD
tube for NIOSH method 5515
63
The 300 mm hemispherical breathing zone for positioning of
the personal sampling head (Victorian Workcover Authority,
2000)
65
Contents of the 1-OHP in urine sampling kit provided to study
participants at the beginning of each sample run
71
Figure 3.23:
Enzymatic development of the metabolite 1-OHP
72
Figure 4.1:
Static air BSF measures in the anode plant, anode plant forming
area, anode plant non-forming area and reconstruction area in
a prebake smelter in Queensland, Australia, 2002–04
83
Figure 4.2:
Personal air BSF measures of workers in the anode plant, anode
plant forming area, anode plant non-forming area and
reconstruction area in a prebake smelter in Queensland,
Australia, 2002–04
83
Figure 4.3:
1-OHP in urine of workers in the anode plant, anode plant
forming area, anode plant non-forming area and reconstruction
area in a prebake smelter in Queensland, Australia, 2002–04
84
Figure 5.1:
Mechanical equipment technician performing maintenance on
the anode former (Photograph taken after implementation of
several changes to the requirement of PPE; note use of Tyvek®
coveralls and impermeable gloves)
116
Figure 3.16:
Figure 3.17:
Figure 3.18:
Figure 3.21:
Figure 3.22:
x
Abbreviations
1-OHP
1-hydroxypyrene
AAC
Australian Aluminium Council
ACGIH
American Conference of Governmental Industrial Hygienists
ANOVA
analysis of variance
ATSDR
Agency for Toxic Substances and Disease Registry
BaP
benzo[a]pyrene
BEI
biological exposure index
BEL
biological exposure limit
BHP
Broken Hill Proprietary
BSF
benzene-soluble fraction
BSM
benzene-soluble matter
ºC
degree Celsius
cr
creatinine
CTPV
coal-tar pitch volatile
EHL
Environmental Health Laboratory
eq
equivalents
Eq
equation
FID
flame ionisation detector
g
gram
h
hour
HPLC
high-performance liquid chromatography
IARC
International Agency for Research on Cancer
ID
internal diameter
IPAI
International Primary Aluminium Institute
J
joule
kg
kilogram
kPa
kilopascal
L
litre
m3
cubic metre
mg
milligram
min
minute
mL
millilitre
mm
millimetre
NATA
National Association of Testing Authorities
xi
ng
nanogram
NIOSH
National Institute of Occupational Safety and Health
NOHSC
National Occupational Health and Safety Commission
OEL
occupational exposure limit
OHS
occupational health and safety
OSHA
Occupational Health and Safety Administration
P450
cytochrome P450
PAC
polycyclic aromatic compound
PAH
polycyclic aromatic hydrocarbon
PPE
personal protective equipment
PTFE
polytetrafluoroethylene
PVC
polyvinyl chloride
RF
reduction factor
RPF
relative potency factor
SD
standard deviation
SEG
similar exposure group
TEF
toxic equivalence factor
TLV®
threshold limit value®
TWA
time-weighted average
UV
ultraviolet
UVA
ultraviolet A
V
volume
µg
microgram
µg
micrograms
µL
microlitre
µm
micrometre
µmole/mol cr
micromole per mole creatinine
xii
Statement of Original Authorship
The work contained in this thesis has not been previously submitted to meet the
requirements for an award at this or any other higher education institution. To the
best of my knowledge and belief, the thesis contains no material previously
published or written by another person except where due reference is made.
Signed:
_____________________________________
Date:
_____________________________________
xiii
Acknowledgements
I would like to gratefully acknowledge my principal supervisor Professor Beth
Newman and associate supervisor Dr Diana Battistutta for all their assistance and
patience over the years.
My sincere thanks also go to Dr Gerry Walpole who was there with guidance and
encouragement from day one until the finish of the project.
I would also like to acknowledge the occupational health team at the smelter for
their continued support in the many sampling programs undertaken across the site
over the duration of the project as their assistance was a key factor in the success of
the monitoring program. Also the leadership team at the smelter who were
supportive of what was a relatively new concept and were always keen to try new
ideas to improve their control programs.
Many thanks to those employees in Reconstruction and Carbon who participated in
the program over the years, wore the monitoring pumps and provided the necessary
samples as required. Many of the control ideas were developed by them as they
went about their work.
And finally to my family, Ellen, Luke, Claire and my ever patient wife Gillian, for
all they have put up with over the life of this thesis and all those weekends lost.
I owe them much.
xiv
1.0 INTRODUCTION
Advances in modern industrial technology have played a major role in the social and
economic progress of many nations. Associated with these technological advances
can be the generation of health hazards with varying levels of impact; some of these
hazards are easy to identify, but others are discovered only after significant research
and investigation. It is important to identify and characterise potential harmful
industrial exposures to individuals and the tasks or environments that generate them,
and to develop methods to eliminate or control these exposures. The aluminium
industry is one in which the process of production has potential to impact on the
health of individuals associated with it.
Developed in the mid-1800s, aluminium production is a relatively new industry. The
Australian aluminium industry has grown dramatically since 1955 when production
commenced at the Bell Bay smelter in Tasmania. By 2007, Australia accounted for
5.2% of world production of primary aluminium, produced 67 million tonnes of
bauxite and was the world’s leading producer of alumina, and delivered 19 million
tonnes of metallurgical or smelter-grade alumina, which is 26% of global production
(AAC, 2007). According to the Australian Aluminium Council (AAC), since 1990
alumina production has increased by 70% and aluminium production by 58%. In
2007, the economic contributions of aluminium production to the Australian
economy included direct employment of 17,000 workers, a capital replacement value
of more than $30 billion, and exports of alumina and aluminium valued at $11.2
billion (AAC, 2007).
1.1
Background to the research
In 1775, Sir Percival Pott, an English surgeon, published the first detailed description
of an occupationally-induced cancer – chimney-sweeps’ cancer of the scrotum. This
was attributed to soot penetrating the clothing of chimney sweeps and poor hygiene
practices, resulting in prolonged contact of the scrotal skin where cancers were
1
developed (Pott, 1775). Chimney soot is now known to contain high levels of
polycyclic aromatic hydrocarbons (PAHs) (Doll, 1975). In 1918, two Japanese
scientists, Yamagiwa and Ichikawa, induced skin cancer in rabbits using coal tar
(Pickering, 1999). Repeated application of crude coal tar, which contains PAHs, to
the ears of rabbits for several months produced benign, and later malignant,
epidermal neoplasms.
1.1.1 What are polycyclic aromatic hydrocarbons (PAHs)?
PAHs are ubiquitous contaminants in the environment. They are also referred to as:
PNAs (polynuclear aromatics),
PACs (polycyclic aromatic compounds) and
POM (polycyclic organic matter).
PAHs are a mixture of organic compounds comprised of aromatic hydrocarbons. The
major building block of their structure is the benzene ring, resulting in molecules
containing fused-ring systems. This structure includes the most basic two-ring
naphthalene or four-ring pyrene and higher five-ring benzo[a]pyrene and six-ring
dibenzo[a,e]pyrene molecular compounds (Figure 1.1). PAHs with three or fewer
benzenic ring structures exist predominately in the vapour phase with boiling points
between 217 and 295ºC. Those with four rings can exist in both the vapour and
particulate phases. Where the compound comprises five or more rings with boiling
points greater than 375ºC, they mainly exist in the particulate phase (Cirla et al.,
2007). The key carcinogenic PAH compounds of interest tend to be in the 4-6 ring
structures, i.e., benzo(a)pyrene. There are hundreds of different configurations with
some sources claiming up to 500 different PAH constituents (Lauwerys & Hoet,
2001); however, the vast majority of these compounds are rarely monitored. The
most common approach by regulatory and institutional bodies is to concentrate on a
limited number of key PAHs. The most common groupings are:
• acenaphthene
•
acenaphthylene
•
anthracene
•
benz[a]anthracene
•
benzo[a]pyrene
2
•
benzo[e]pyrene
•
benzo[b]fluoranthene
•
benzo[g,h,i]perylene
•
benzo[j]fluoranthene
•
benzo[k]fluoranthene
•
chrysene
•
dibenz[a,h]anthracene
•
fluoranthene
•
fluorene
•
indeno[1,2,3-c,d]pyrene
•
phenanthrene
•
pyrene
Naphthalene
Pyrene
Benzo(a)pyrene
Dibenzo(a,e) pyrene
Figure 1.1: PAH ring structures of naphthalene, pyrene, benzo[a]pyrene and
dibenzo[a,e]pyrene (Freeman, 2008)
PAHs are formed when natural or synthetic organic materials incompletely combust
with oxygen. They are derived from the elements of carbon and hydrogen. PAHs do
not generally exist in the environment as discrete compounds, but are found as
3
complex mixtures of many different concentrations and compositions. Sources can
include motor vehicle combustion engines, residential coal- or oil-fired heating
systems, industrial environments, and natural sources such as bush fires and
volcanoes. PAHs also can be found in substances such as crude oil, coal, coal-tar
pitch, creosote, dyes, plastics, pesticides and, in a few instances, medical
preparations. Due to their low vapour pressures, most PAHs entering the atmosphere
as vapour will be adsorbed onto existing particles, condense on particles such as soot
or form very small particles themselves. Their presence in the environment is not
restricted to the air; they are often found in surface waters as a result of airborne
fallout or industrial discharges, and also in the soil. Human exposure occurs through
a variety of sources, including diet, tobacco smoking, pollution and occupational
exposure. The route of entry to the body may be via inhalation, ingestion or dermal
absorption.
Coal tars are a viscous black or dark brown material byproduct formed during the
destructive distillation of coal in a process known as carbonisation, or coking. They
contain high-molecular-weight hydrocarbons, such as benzene, toluene, phenol,
styrene, cresol, naphthalene and numerous PAHs, which volatilise when heated
(Kurtz, Verma, & Sahai, 2003). The composition and properties of a coal tar depend
primarily on the temperature of the carbonisation process and, to a lesser extent, on
the nature (source) of the coal used as feedstock. In general, coal tars are complex
combinations of hydrocarbons, phenols, and heterocyclic oxygen, sulphur and
nitrogen compounds. More than 400 compounds have been identified in coal tars,
and as many as 10,000 may be present. The content of PAHs in coal tars increases as
the carbonisation temperature increases (ATSDR, 2002). Low-temperature coal tars
(formed at temperatures below 700°C) contain a lower percentage (40–50%) of
aromatic compounds than high-temperature coal tars (formed at temperatures above
700°C) (IARC, 1984).
1.1.2 PAH carcinogenicity associated with aluminium smelting
Since Pott’s (1775) keen observations, other cancers related to exposure to PAHcontaining compounds have been identified. The International Agency for Research
on Cancer (IARC) determined that key PAHs – benz[a]anthracene and
4
benzo[a]pyrene – are probably carcinogenic to humans; benzo[b]fluoranthene,
benzo[j]fluoranthene, benzo[k]fluoranthene and indeno[1,2,3-c,d]pyrene are possibly
carcinogenic to humans (IARC, 2005). Several epidemiological studies have
revealed an increased mortality risk for neoplasms among workers exposed to
mixtures of chemicals containing PAHs.
In 1984, the IARC evaluated the carcinogenic risk of PAHs in industries, including
primary aluminium production, coal gasification, coke production, and iron and steel
founding. A cancer risk associated with the primary aluminium production process
was identified:
A number of individual polynuclear aromatic compounds for which there
is sufficient evidence of carcinogenicity in experimental animals have
been measured at high levels in air samples taken from certain areas in
aluminium production plants. Taken together, the available evidence
indicates that certain exposures in the aluminium production industry are
probably carcinogenic to humans (IARC, 1984).
It is important to note that the above statement is directed at aluminium smelting in
general; levels of exposure can vary dramatically between different aluminium
smelting processes. The 1984 IARC monograph did not differentiate between the
two processes employed in the aluminium industry – the ‘Söderberg’ and the
‘prebake.’
Exposure to PAHs occurs during several tasks in the occupational environment of an
aluminium smelter. The main source of exposure to PAHs is coal-tar pitch, which is
used as a binding agent for the carbon anodes and cathodes, and utilised in the
reduction cell (Figure 1.2). During the production of these components, there are
varying exposures to PAHs via inhalation, ingestion and dermal adsorption.
Konstantinov and Kuz’minykh (1971) found that concentrations of benzo[a]pyrene
(BaP) generally were lower in the prebake reduction line than in the Söderberg
reduction line, and that pitch-volatile concentrations were lower in carbon plant areas
associated with prebake facilities than in the Söderberg reduction line. Bjørseth,
Bjørseth and Fjeldstad (1978) also found PAH levels to be lower in prebake
smelters; importantly they determined that a higher fraction of PAHs in the
5
Söderberg samples belonged to the higher-boiling, more hazardous PAH compound
BaP than in the prebake anode facilities.
Konstantinov and Kuz’minykh (1971) compared cancer mortality rates from
Söderberg and prebake primary aluminium production plants in the USSR. Excesses
of all cancers and of lung cancer specifically were claimed for the Söderberg-process
Figure 1.2: Prebake aluminium reduction cell showing key components including
anodes and cathodes (Boyne Smelters Ltd, 2001)
workers, and an increased incidence of skin cancer was reported, particularly among
young workers (IARC, 1984). Konstantinov, Simakhina, Gotlib and Kuz’minykh
(1974) conducted further cancer mortality studies among reduction line workers in
three aluminium plants, two using the Söderberg process and the other using the
prebake process. Elevated ratios for lung cancer were reported in both Söderberg
plants and for skin cancer in one Söderberg plant. No elevated ratios for lung or skin
cancer were associated with the prebake plant. Milham (1979) noted an increase in
the standardised mortality ratio in workers at a prebake smelter in Washington State
for cancer of the pancreas and for lymphoma. Exposure was defined as occurring in
carbon plants manufacturing anodes, relining or reconstruction of potrooms.
6
The existence of an association between exposure to coal-tar pitch volatiles (CTPV)
in Söderberg potrooms and excess risk of bladder cancer has been established in
several studies (Gibbs & Horowitz, 1979; Theriault, Cordier, Tremblay, & Gingras,
1984; Armstrong, Tremblay, Cyr, & Theriault, 1986). A case-control study in
Chicoutimi, Quebec, revealed an increased risk of bladder cancer associated with
employment in the reduction line of an aluminium plant that utilised the Söderberg
technology (Theriault, De Guire, & Cordier, 1981). This association in those who did
not smoke cigarettes (relative risk 1.90) was not much greater than the association
between cigarette smoking and bladder cancer (relative risk 1.82); however, those
aluminium reduction process workers who smoked cigarettes had a much higher
relative risk (5.70) (Theriault et al., 1981). Tremblay, Armstrong, Theriault and
Brodeur (1995) also demonstrated a clear association between bladder cancer and
work in Söderberg smelter potrooms and cumulative exposure to CTPVs.
In an extension of Gibbs’ (1985) study of the mortality of aluminium reduction plant
workers, Armstrong, Tremblay, Baris and Theriault (1994) investigated the
association between exposure and lung cancer in a case-cohort study of men who
worked at least one year in manual jobs at a large aluminium smelter. The authors
found that lung cancer rate ratios rose with cumulative exposure to CTPVs measured
as benzene-soluble material (BSM), and predicted a lifelong excess risk of 2.2%
after 40 years exposure at the current hygiene standard (0.2 mg/m3). The plant in this
study employed both Söderberg and prebake types of cells, making it difficult to
ascertain the respective influences of the technology in use.
A meta-analysis prepared for the UK Health and Safety Executive (Armstrong,
Hutchinson, & Fletcher, 2003) supported conclusions of previous studies that
associated lung cancer with PAH exposure. While results for bladder cancer were
not conclusive, predominately due to the much lower incidence of this cancer, a
positive association of bladder cancer with the aluminium production industry was
reported. A correlation between the aluminium industry and bladder cancer was
reported also by Negri and La Vecchia (2007); however, it should be noted that this
association was based on only two studies of aluminium production workers
(Romundstad, Haldorsen, & Andersen, 2000; Tremblay et al., 1995).
7
A recent study undertaken in two prebake smelters in Australia found no excess of
cancer or mortality; however, there was elevation of risks to incident mesothelioma
and kidney cancer (Sim et al., 2009).
1.2
Research contribution
Historically, research on occupational PAH exposure has taken place in a variety of
settings, such as chimney sweeping, firefighting, paving industries and laboratories,
however the composition of the pitch used in these settings can be quite different
from that used in aluminium smelting. Studies relating to exposure to PAHs in
aluminium smelting have tended to focus on the Söderberg process rather than the
prebake process due to the higher levels within the Söderberg reduction lines.
However, there are areas of potential exposure within the prebake process,
particularly associated with the build of the reduction cells, i.e. the cathode and
anode construction, which are addressed in this thesis. Moreover, previous limited
research in modern prebake aluminium smelters has largely taken place overseas,
failing to address the specific work conditions present in Australian plants,
Australian work and safety guidelines, and the Australian climate, all of which are
relevant to occupational health standards in this country.
This study quantifies the levels of static and personal airborne exposure across the
two key exposure areas of a prebake aluminium smelter in Queensland, Australia. It
investigates correlations between airborne and biological levels to elucidate the
exposure profile in a prebake smelter, in particular what are the important routes of
exposure, proposes the most effective monitoring approach and suggests where
measures to ameliorate risk associated with exposure to PAHs in the primary
aluminium production process may be instigated. Several research questions are
addressed:
•
What are the comparative levels of airborne exposure associated with
reconstruction of the carbon cathode lining in the cell and the manufacture of
the carbon anode?
•
Is there a significant exposure risk associated with routes other than air in
primary aluminium prebake smelting?
8
•
What contribution to exposure risk do skin contact and ingestion of
particulates/residues represent?
•
Is the focus on airborne monitoring of PAHs (e.g. BSF and/or BaP) in the
aluminium industry adequate to accurately characterise total occupational
exposure to PAHs?
Although biological monitoring can provide a measure of combined exposures from
all routes and is being used at some sites, it has not been adopted as a routine method
for exposure characterisation in this industry because the key route of exposure is
still regarded as airborne. As occupational exposure limits for PAHs only exist for
airborne contaminants, all regulatory and surveillance process-control monitoring is
undertaken using personal air sampling or static sampling. Both of these methods are
utilised in this study as they are the current methodology in use in the primary
aluminium industry. Although international guideline values exist, no biological
exposure limits for PAHs are used by a regulatory body in Australia.
To identify where the higher levels of exposure to PAHs occur in a prebake smelter,
exposures of workers comprising similar exposure groups (SEGs), utilising static
and personal air monitoring and biological monitoring to measure the PAH exposure
levels, were compared. The relationships of these SEGs within the smelter are
illustrated in Figure 1.3. Reduction line or potline workers were not included in this
assessment due to limited time and resources, however, previous monitoring
undertaken at the smelter indicated low levels of exposure in the reduction line.
9
Non Production
Aluminium
Smelter
Anode Plant
Reconstruction
Forming
Non-forming
Figure 1.3: Relationship of SEGs studied within the prebake smelter
1.2.1 Aims and objectives
Airborne monitoring of PAHs has been the standard recommended approach for risk
assessment where there is a potential for exposure to products or processes allied
with PAHs. Static monitoring has been utilised to assess the potential fugitive
emissions of the plant and process whilst personal monitoring of the individuals has
been compared with known exposure standards utilised by many regulatory and nongovernment bodies.
The primary aim of this study was to investigate whether airborne monitoring
methods, accepted as the “gold” standard method for exposure assessment to PAHs,
are still the most appropriate approach for the monitoring of exposure to PAHs in a
pre-bake aluminium smelter and whether there has been any value added by the
inclusion of biological monitoring. Furthermore, it was anticipated that a study of
worker exposure to PAHs at this plant could serve as a model for biological
monitoring of human-process interactions where fugitive CTPVs represent an
occupational hazard.
10
Specific objectives of this study were:
1. To investigate the exposure levels of five similar exposure groups (SEGs) to
airborne PAHs utilising both static and personal monitoring methods
specifically within prebake smelting.
2. To evaluate the utility and benefit of monitoring 1-hydroxypyrene (1-OHP)
in urine of workers as a routine method for determining exposure to PAHs in
an anode-manufacturing facility in a modern prebake aluminium smelter.
3. To correlate the BSF of airborne samples, both static and personal, with the
level of 1-OHP in urine of the workers in the plant.
4. To assess the contribution of non-respiratory PAH exposure, i.e. skin contact
and particulate ingestion, to total body burden within a pre-bake aluminium
smelter.
5. To evaluate whether the airborne monitoring of BSF or the biological method
for 1-hydroxypyrene monitoring, either in isolation or as a multi-factorial
exposure regime, is the most appropriate method for monitoring PAH
exposure in a prebake aluminium smelter.
1.2.2 Hypotheses
This project is of sufficient size to test the following alternative hypotheses with
adequate statistical power. In a prebake smelter, based on the results of static air
monitoring of the process, personal air monitoring of the individual and biological
monitoring:
1. Workers in the carbon anode plant will have higher exposure to PAHs than
workers in the cell-reconstruction area of the smelter.
2. Within the carbon anode plant, exposure to PAHs will be higher among
workers involved in tasks associated with the paste-mixing and anodeforming areas than those in the non-forming areas of the carbon anode plant.
3. There is no evidence of a relationship between personal air monitoring for the
BSF and 1-OHP in urine of workers involved with tasks in a prebake smelter.
11
1.3
Thesis outline
Chapter 2 of this thesis reviews the literature in relation to the differing routes of
exposure to PAHs and the monitoring of those exposures. It considers the
applicability of biological exposure indices and how these are calculated for specific
environments. The chapter concludes with a review of the role of biological effect
monitoring in the assessment of exposure to PAHs and risk quantification.
Chapter 3 outlines the research methods used to achieve the study objectives. After
explaining the study site and the aluminium reduction process, it describes the
exposure groups and study participants, and provides details of air and biological
monitoring sample collection and analysis, and data management and statistical
analysis.
Chapter 4 presents the results for air and biological monitoring for the particular
areas of interest in the prebake aluminium smelter. Statistical relationships are
examined, and the results from comparison of the data sets in relation to the three
hypotheses are presented. Also included are results from data collected before and
after a plant process intervention.
Chapter 5 discusses the research findings, and examines the results in relation to
other relevant studies. Strengths and limitations of the study are considered, and
recommendations are made for future research and implementation of control
measures.
12
2.0 LITERATURE REVIEW
In 1984, the IARC listed employment in the primary aluminium industry as an
occupation where there are exposures to compounds that are carcinogenic to humans,
potentially giving rise to cancer of the lung and bladder (IARC, 1984). Based on
multiple studies carried out within the aluminium industry around the world prior to
1984, the IARC identified pitch fume as a possible causative agent and, to date, has
not reviewed this classification. With a selection of literature relating to PAH
carcinogenicity associated with aluminium smelting reviewed in section 1.1.2, this
chapter focuses on the routes of exposure to PAHs and the monitoring of those
exposures.
There have been a number of studies that examine PAH exposure and its assessment
both biological and via inhalation over the years with some of these having been
based in varied environments, such as chimney sweeping (Pavanello et al., 1999) and
firefighting (Moen & Øvrebø, 1997), and others have been in controlled
environments, such as laboratories (van Rooij et al., 1993b; Clonfero et al. 1989).
Some ( Jongeneelen (2001); Unwin, Cocker, Scobbie, & Chambers, 2006) examined
PAH exposure across several industries and occupations. These and a number of
other studies that are referenced in this thesis have assessed PAH exposure from a
number of different perspectives and across industries.
Borak et al. 2002; McClean et al. 2004; Cirla et al. 2007, focussed on the paving
industries and whilst there are some similarities in the exposures and the analysis
undertaken, it is important to note that the composition of the pitch component in the
paving and asphalt industries has a lower proportion of PAHs and is quite different
from that used in the aluminium industry as is the Boogard et al. 1993 study based
around the petrochemical industries looking at the manufacture and maintenance
operations. The work undertaken in the carbon or graphite anode plants by Angerer,
et al. (1997) provide a number of useful parallels for this study, however, again there
are aspects missing that need to be addressed for the Australian context. In
particular, the occupational exposure limit used in the Australian workplace is that of
BSF whereas the Angerer paper undertook comparisons with specific components
such as pyrene, phenanthrene and benzo(a)pyrene, which is more relevant for the
German environment as they have an exposure limit for benzo(a)pyrene. Without
13
knowing the composition of the parent pitch compound, comparison with the
aluminium industry is difficult. An anode graphitisation plant is also quite different
from a prebake aluminium anode plant or cathode reconstruction process. The work
by van Rooij et al., (1994a), (1993a); Buchet, Gennart et al. (1992); Wu et al. (1998);
Jongeneelen, (1992) are all coke oven studies which provide valuable insight into the
characteristics of exposure to PAHs, the history of the development of the 1hydroxypyrene biological monitoring process and establish correlations between air
exposure and biological monitoring. However, the exposure profile of a coke oven is
quite different to that of a prebake aluminium smelter and caution needs to be
exercised when drawing comparisons. It is here where the studies undertaken by van
Rooij et al., (1992); Friesen et al, (2008) Tjoe Ny et al. (1993) and Jessep (2007),
help fill in some of the gaps. Whilst all of these studies were undertaken at primary
aluminium smelters, which is the area of interest, with the exception of Jessep
(2007), each of these were plants employing the Söderberg technology, which is
quite different to the modern pre-bake process used at the smelter which is the
subject of this study (see section 3.2 Study context – plant process description). This
is an important aspect as previously discussed in section 1.1.2 as many of the
epidemiological studies undertaken over the years which have shown a relationship
between PAH exposure in aluminium smelting and cancer (Gibbs & Horowitz, 1979;
Theriault, Cordier, Tremblay, & Gingras, 1984; Armstrong, Tremblay, Cyr, &
Theriault, 1986) were undertaken at Söderberg smelters not prebake. The report by
Jessep (2006) is the most similar study having been based at a relatively modern prebake smelter, carbon anode plant in the United Kingdom. The key differences being
that the anode plant configurations were different, with the UK plant being a
batching plant and the Australian, a continuous operation plant. The climates at the
two locations were dramatically different, the UK plant being cold/temperate and the
Australian sub-tropical. Also, the exposure associated with cell reconstruction was
not considered and a comparison of the BSF and biological data was not undertaken.
2.1
Routes of exposure
Occupational exposure to PAHs may occur via three different routes: inhalation,
ingestion and skin absorption (ATDSR, 1995). The main route of exposure will be
14
dependent on the environment, process, work practices and, in some cases, the level
and type of PPE worn. The route of exposure to PAHs can play a major role in their
fate within the body. Inhaled compounds may bypass the liver and reach peripheral
tissues in higher concentrations than would be seen via oral exposures (ACGIH,
2005). To date, the predominant method of assessment of exposure to PAHs has
been the monitoring of contaminant levels in the air. This method is based on the
assumption that the key route of exposure is via inhalation and does not consider
ingestion or skin absorption as discussed below.
2.1.1 Inhalation
Although occupational studies have shown that humans absorb inhaled PAHs, the
extent of the absorption is unknown. Some animal studies have indicated that this
absorption may be affected by the medium on which the PAHs are being transported
(Gerde & Scholander, 1989; ATDSR, 1995). This absorption occurs through the
mucous lining of the bronchi. As PAHs are generally lipophilic, they can cross the
lungs through passive diffusion and partitioning into lipids and water of cells (Gerde,
Medinsky, & Bond, 1991). Creasia, Poggenburg and Nettesheim (1976) showed that
the elimination of benzo[a]pyrene (BaP) from the lungs following intratracheal
administration of pure BaP crystals and BaP-coated carbon particles varied; while
50% of the pure BaP crystals was cleared from the lungs within 1.5 hours and more
than 95% cleared within 24 hours, only 50% of the BaP that was adsorbed onto the
carbon particles had cleared within 36 hours. The clearance period was even longer
for the larger particle size carbon (4–5 days). This indicates that the bioavailability of
BaP is affected by the nature of the carrier and the particle size. Gerde and
Scholander (1989) concluded that the rate-determining step in the transport of PAHs
from particles to the bronchial epithelium is the release rate of the PAHs from the
carrier particles. Becher and Bjørseth (1983) found that the high concentration of
PAHs in an occupational setting did not correlate with the results of the amount
found in the testing of the subjects’ urine samples. They concluded that PAHs
adsorbed to airborne particulate may not be readily bioavailable and that the doseuptake relationship may vary over the PAH concentration range. Whilst this is a
feasible conclusion, Becher and Bjørseth (1983) did not indicate whether subjects
used respiratory PPE.
15
2.1.2 Ingestion
There is limited information available in relation to exposure to PAHs via ingestion;
the majority of occupational exposure studies focus on inhalation or dermal routes. It
is known that consumption of some foods results in the detection of metabolites in
the urine. Factors affecting the concentration of PAHs in food include the location in
which it was grown, the manner of preparation, the time of exposure to and distance
from heat sources, and the use of fat (IARC, 1973). Approximately 100 PAHs have
been found in smoked fish, and concentrations of up to 2.0 µg BaP per kg smoked
fish have been detected (Zedeck, 1980). The effect of a diet that may contain high
levels of PAHs impacts on urinary 1-hydroxypyrene (1-OHP) levels to a lesser
extent. Borak, Sirianni, Cohen, Chermerynski and Jongeneelen (2002) found that
levels of 1-OHP in urine did not differ significantly among creosote facility workers
who did and did not eat grilled foods, and the number of grilled servings was
unrelated to urinary 1-OHP. Where there is a low environmental exposure, grilled
food consumption is likely to be more easily detected, and where there are other
significant sources such as occupational exposure, the impact of food is less likely to
be distinguished from total body burden. In relation to oral absorption, it is known
that uptake will increase with an increase in the lipophilic nature of the compound or
the presence of oils in the gastrointestinal tract. Busbee, Norman and Ziprin (1990)
found that virtually all gastrically instilled BaP is absorbed via uptake of fat-soluble
compounds.
2.1.3 Skin absorption
Over the years, mixtures of PAHs have been used to treat skin conditions and
disorders in humans, providing substantial data describing the dermal effects of PAH
exposure. Percutaneous absorption of PAHs appears to be rapid for both humans and
animals, but can depend on the solvent (ATDSR, 1995).
PAHs tend to accumulate in membranes and thus impact cell function if not removed
(Klaassen, 2001). They are hydroxylated by cytochrome P450 isozymes in epidermal
cells. Oxidative biotransformation, however, produces electrophilic epoxides that
16
can form DNA adducts. Phenols produced by re-arrangement of the epoxides can be
oxidised further to quinones, resulting in active oxygen species, and they are also
toxic electrophiles (Klaassen, 2001).
In an investigation of exposure among paving workers utilising skin contamination
monitors, Jongeneelen et al. (1988c) found a correlation that indicated the internal
doses might be affected by dermal exposure. A study of anode plant workers in an
aluminium reduction plant in the Netherlands (van Rooij, Bodelier-Bade, de Looff,
Dijkmans, & Jongeneelen, 1992) found the total skin contamination in exposed
workers was estimated to be more than three times higher than the intake via the
respiratory tract. From measurements taken on exposure pads located at six skin sites
(jaw/neck, shoulder, upper arm, wrist, groin, ankle), van Rooij, Bodelier-Bade,
Hopmans and Jongeneelen (1994a) reported that skin contact accounted for
approximately 75% of total absorbed pyrene in a study of coke oven workers, not
only on the uncovered skin but also on skin covered with working clothes. The
authors concluded that the latter was probably due to contact with contaminated
clothing rather than deposition from the air. In a study of PAH exposure among
asphalt paving workers, McClean et al. (2004) estimated that dermal exposure was
eight times the impact of inhalation exposure. Similar results were reported by Borak
et al. (2002) in their study of creosote facility workers. Van Rooij, De Roos,
Bodelier-Bade and Jongeneelen (1993b) demonstrated low but significant
differences in the dermal PAH absorption between anatomical sites listed in Table
2.1. Also of note is the potential impact on percutaneous absorption by such factors
as hydration, friction or temperature.
17
Table 2.1: Absorption indices of pyrene and PAH for different anatomical sites
(Adapted from van Rooij et al., 1993b)
Anatomical site
Pyrenea
PAHb
Arm
1
1
Hand
0.8
0.5
Leg/ankle
1.2
0.8/0.5
Trunk/shoulder
1.1
2.0
Head/neck
1.3
1.0
a
Based on excreted amount of 1-OHP in urine after coal-tar
ointment application
b
Based on the PAH absorption rate constant (Ka) after coal-tar
ointment application
Within industries associated with coal-tar pitch, there are particular skin reactions
that often manifest amongst workers. One of these reactions, colloquially referred to
as ‘pitch burn,’ is a form of phototoxicity that results in delayed erythema and skin
pain. This sensitisation was first recognised by Lewin (1913), who described
“workers in contact with coal-tar products who developed dermatitis and itching
upon exposure to sunlight.” In 1930, Fleischauer demonstrated “that even 15 min of
tar application resulted in photo sensitivity to irradiation with a quartz lamp or
sunlight through window glass” (Diette, Gange, Stern, Arndt, & Parrish, 1983). The
presence of pitch burn within an industry is often an indication that there are issues
with exposure to PAHs, hence the reporting of such instances should be monitored
and could possibly be used as a gauge of control effectiveness. Figure 2.1 illustrates
this time effect in relation to pitch exposure and phototoxicity. The phototoxic dose
is the minimum level of UVA required to produce delayed erythema of the skin. The
x-axis refers to the length of time the 5% crude coal tar mixture was allowed to
remain in contact with the skin.
18
Minutes of Tar application vs Dose of UVA required for reaction
(Adapted from Diette, K.M., et al Coal Tar
Phototoxic Dose (J/cm2) UVA
25
Phototoxic dose required with no pitch on
skin exposure for an erythema
20
After 15 minutes skin contact 2/3 of the
dose of UV required for an erythema
15
After 30 minutes skin contact only 1/2 of the level
of UV required for an erythema
10
After 60 minutes skin contact less than a 1/4
of the level of UV required for a erythema
5
0
0
15
30
60
90
120
180
Time (minutes)
Figure 2.1: Level of dose of UVA required for a reaction on the skin in relation to
varying lengths of skin contact time with coal-tar pitch (Adapted from Diette et al.,
1983)
An additional method that has been employed at a smelter in Australia was the use of
ultraviolet light to identify areas of the skin where exposure and contact has taken
place (A. Riley, personal communication, 2004). In the presence of ultraviolet light,
areas contaminated with tar fluoresce and are easy to identify. This method has been
used as a training tool to illustrate where contact is occurring and the effectiveness of
general hygiene practices such as hand washing and showering. A study undertaken
in the early 1990s used this tool to prepare ‘skin maps’ of exposure of workers to
determine possible causes or sources of contact in the different tasks. Whilst a formal
report was never completed, the results revealed that certain tasks led to higher levels
of skin contact with the areas of highest contamination around the wrists, head and
neck. This identification method has proved to be of value and is still in use at the
site (A. Riley, personal communication, 2004).
19
2.2
Measures of PAH biological effect
Of the PAH groupings listed in section 1.1.1, the carcinogenic potency tends to be
highest amongst those particle-bound PAHs (4-6 ring compounds), the most notable
being:
•
benzo[a]anthracene,
•
benzo[b]fluoranthene,
•
benzo[k]fluoranthene,
•
benzo[a]pyrene,
•
dibenz[a,h]anthracene,
•
benzo[g,h,i]perylene and
•
indeno[1,2,3-c,d]pyrene.
Benzo[a]pyrene (BaP) is the most prominent carcinogen and the one most often used
as an index of toxicity (Rappaport, Waidyanatha, & Serdar, 2004). BaP is the parent
carcinogen that requires metabolic activation by cellular enzymes or cytochromes,
such as P450, to form BaP-7,8 epoxide, which is then hydrated by epoxide hydrolase
to form BaP-7,8-diol (Hodgson & Smart, 1985). This metabolite is considered to be
the proximate carcinogen (intermediate metabolite), which is then further
metabolised by cytochrome P450 to form the ultimate carcinogen, the bay region
diol epoxide, (+)-BaP-7,8-diol-9,10-epoxide-2. The bay region theory suggests that
the bay region diol epoxides are the ultimate carcinogenic metabolites of PAHs
(Hodgson & Smart, 1985). This process is illustrated in Figure 2.2.
(-)-BP-7,8-Diol-9,10-Epoxide-2
O
(-)-BP-7,8-oxide
Epoxide Hydrolase
P-450
P-450
O
Benzo(a)pyrene
HO
OH
HO
OH
(+)-BP-7,8-Dihydrodiol
Figure 2.2: Metabolism sequence of BaP to the bay region diol epoxide,
(+)-BaP-7,8-diol-9,10-epoxide-2 (Hodgson & Smart, 1985)
20
The actual toxicity level of the components in mixtures of PAHs is difficult to
ascertain because of the possible presence of other toxic compounds that may be
tumour promoters, initiators and/or co-carcinogens in the mixtures. One of the most
important complications is the potential for interaction among the many different
components of the mixture, including synergistic or multiplicative effects in which
the combined effect of two or more substances is greater than the sum or product of
the effects of each agent alone (Klaassen, 2001). This also makes it very difficult to
evaluate the individual contribution of any one compound to the total toxicity and
carcinogenicity of the mixture. Hence, evaluating the risks of exposures to mixed
compounds presents significant problems.
The application of toxic equivalence factors (TEFs) to determine relative potency
factors (RPFs) is often employed when dealing with PAH mixtures. RPF is defined
as the ratio between the airborne concentrations of BaP equivalents to the
concentration of BaP alone (Petry, Schmid, & Schlatter, 1996):
RPF = Conc BaP eq
Conc BaP
Where the sum of the BaP equivalent concentrations (Conc BaP eq) is equal to the
sum of carcinogenic PAH concentrations expressed as BaP multiplied by the TEF of
PAH compound of interest such as those shown in table 2.2.
There is inconsistency in application of RPFs, as they vary from source to source. An
example is presented in Table 2.2, which includes five different variations of RPFs
currently in use. Petry et al. (1996) produced an additional four lists from different
sources. Added to this is the inconsistent and incorrect interchangeable use of the
terms, relative potency, RPF and TEF in the literature. Petry et al.’s (1996) table of
TEFs referred to Thorslund and Farrer’s TEFs which were duplicated in Willes,
Friar, Orr and Lynch (1992) but referred to as RPFs as illustrated in table 2.2. The
confusion can arise due to the similarity of the terminology used as the relative
21
potency of a compound is measured by the TEF and this can be used to determine a
relative potency factor.
Table 2.2: Comparison of RPFs for PAHs (Willes et al., 1992)
Source
PAHs
ATSDR
1995
1.0
Krewski
et al.,
1989
1.0
Thorslund
& Farrer,
1991
1.0
Rugen
et al.,
1989
1.0
Willes
et al.,
1992
1.0
benzo[a]pyrene
benzo[e]pyrene
NDA
0.004
0.007
NDA
0.05
benzo[a]anthracene
0.145
0.145
0.145
0.006
0.033
benzo[b]fluoranthene
0.167
0.14
0.12
0.02
0.1
benzo[k]fluoranthene
0.020
0.066
0.052
NDA
0.01
benzo[g,h,i]perylene
NDA
0.022
0.021
NDA
1.0
Chrysene
0.0044
0.0044
0.0044
NDA
0.26
dibenz[a,h]anthracene
1.11
1.11
1.11
0.60
1.4
fluoranthene
NDA
NDA
NDA
NDA
0.034
indeno[1,2,3-c,d]pyrene
0.055
0.232
0.278
0.006
0.1
Pyrene
NDA
0.081
NA
NDA
NA
NDA = no data available; NA = Not applicable as not regarded as a genotoxic carcinogen
2.3
Exposure monitoring
Human exposure monitoring in relation to carcinogenic chemicals is used to:
•
establish and maintain exposure limits;
•
identify populations at risk;
•
elucidate dose-effect relationships; and
•
assess the risk of developing cancer (van Delft, Baan, & Roza, 1998).
In the past, the assessment of exposure to carcinogenic compounds within the
aluminium industry has been heavily slanted towards external exposure monitoring
of the work environment.
22
2.3.1 Air monitoring
In the case of PAHs, the most common air monitoring methods employed are based
on National Institute for Occupational Safety and Health (NIOSH) methods 5042,
5515
and
5506,
which
utilise
a
personal
monitoring
pump
and
a
polytetrafluoroethylene (PTFE) membrane filter with a cellulose support pad in a 37
mm cassette filter holder and, in some cases, combined with an XAD-2® tube
(NIOSH, 1998). Alternatively, the Occupational Safety and Health Administration
method 58 that utilises glass fibre filters can be used (OSHA, 1986). In both cases
the analysis is similar in that filters are analysed by extraction with benzene and then
gravimetrically determine the benzene-soluble fraction (BSF), also known as
benzene-soluble matter (BSM). Where more detailed characterisation of the sample
is required, the presence of specific PAHs is assessed by analysing the sample via
high-performance liquid chromatography (HPLC) with a fluorescence or ultraviolet
detector.
The pump and filter system can be utilised as a static sampler positioned in the
vicinity of a specific work area to assess the performance of a plant or of controls
implemented to reduce the release of contaminants from a particular section of the
process. It is important to note that these results cannot be compared with
occupational exposure standards, as the latter have been developed from
occupational exposure measured via a personal monitoring pump attached to the
individual. Alternatively, and more commonly, the pump and sample filter head are
worn by the process operator, with the filter head positioned in the individual’s
breathing zone, recognised as a 300 mm hemispherical area about the inhalation
zone of the nose and mouth (Victorian Workcover Authority, 2000). This method
assumes the equivalent uptake by the individual. The results obtained from this
analysis may be compared with current occupational exposure standards such as
those listed by the National Occupational Health and Safety Commission (NOHSC,
1995). The NOHSC guidelines are based on those established by the American
Conference of Governmental Industrial Hygienists (ACGIH). This threshold limit
23
value/time-weighted average (TLV/TWA) is listed as 0.2 mg/m3 for BSF (the
recommended occupational exposure limit to CTPVs) which
…is defined operationally in terms of the benzene (or cyclohexane)
extractable fraction of total airborne particulate as collected by a
personal sampler. If the extractable material contains detectable
quantities of ben[a]anthracene, benzo[b]fluoranthene, chrysene,
anthracene, benzo[a]pyrene, phenanthrene, acridine, or pyrene, then the
TLV-TWA for that material is 0.2 mg/m3 total aerosol (ACGIH, 2007).
This method assumes that the PAHs measured as the BSF of the particulate collected
are completely desorbed along with other hydrocarbons in the analysis process. The
method has some shortcomings in that the true carcinogenic potential may be either
overestimated or underestimated, depending on the specific PAHs present in the
mixture, as has been previously discussed in relation to TEFs. An additional
complication is that any other substances that are benzene soluble will be measured
also. It should be noted that methods involving benzene as a solvent are no longer
recommended due to the health implications associated with its use (ATDSR, 2007).
In more recent times, cyclohexane has been used as an alternative in this method
and, whilst effective, does not extract PAHs as effectively as benzene (Harrison &
Thomas, 1987).
The TWA is that exposure over an 8-hour day, for a 5-day working week, over an
entire working life that should neither impair the health of, nor cause undue
discomfort to, nearly all workers (ACGIH, 2007). Whilst the standard is based on an
8-hour day, 40-hour week, the current trend in industry is that the main shift tends to
be of 12 hours duration with a common rotation being two day shifts followed by
two night shifts then four days rostered off. The NOHSC guidance note advises that
the TWA exposure standard may need to be reduced by a suitable factor to take into
account these extended shifts to ensure adequate worker protection (NOHSC, 1995).
A 12-hour work shift involves a period of daily exposure that is 50% greater than
that of the standard 8-hour work-day and the period of recovery before re-exposure
is shortened from 16 to 12 hours. For some systemic toxins having half-lives
between 5 and 500 hours, it can be predicted that working longer than 8-hour shifts
is likely to result in a greater hazard than that incurred during normal work weeks
(Paustenbach, 1994). Models to determine the appropriate adjustment have been
proposed by several researchers, including Brief and Scala, OSHA, Iuliucci, and the
24
pharmacokinetic models of Mason and Dershin, Hickey and Reist (Harris, 2000).
NOHSC (1995) recommended use of the Brief and Scala model due to its simplicity
and effectiveness. It can, however, be considerably more conservative than some of
the other models. It is based on the following equation:
8 x 24 – h
h
16
Where RF is the reduction factor and h is the hours of the shift.
RF =
Hence, for the situation where an employee works a 12-hour shift for 4 days, the RF
would be 0.5. Unfortunately this exposure model is based on inhalation and does not
take into account skin absorption, ingestion, differences in metabolism, bioavailability, distribution, excretion or the use of PPE. Also, there is the issue of
exposure via other sources such as diet, personal health products and cigarette
smoking.
2.3.2 Biological monitoring
A method of estimating an individual’s internal exposure utilises biological
monitoring (Jongeneelen et al., 1988b). This method usually involves the
determination of a parent chemical, which may be representative of a mixture of
chemicals (e.g. pyrene for PAHs), by assessing the level of a metabolite of that
chemical in body fluids (blood or urine) or expired air.
The use of 1-OHP as a biological marker was primarily developed by Jongeneelen
through a range of studies and with some human validation carried out via
therapeutically treated human subjects (Jongeneelen et al., 1985, 1988a,b,c; Tsai,
Shieh, Lee, Chen, & Shih, 2002). Pyrene is metabolised into the intermediary 1-OHP
to form 1-hydroxypyrene-glucuronide, which is excreted (Jongeneelen, Anzion, &
Henderson, 1987). Pyrene is rapidly distributed, metabolised and eliminated from the
body, and 1-OHP is a reliable indicator of systemic exposure to this PAH (Bouchard,
Krishnan, & Viau, 1998). The distribution and metabolism of pyrene within the
body can vary dependent on the route of entry. Ingested pyrene is metabolised in the
liver, with the majority being eliminated in bile as glucuronides; this is quite
different to pyrene absorbed through the skin as it is partially metabolised in the
skin, with the majority being transported via the vascular system to the lungs where
25
it is metabolised to a greater extent (ACGIH, 2005). Pyrene metabolites in the lung
will also be distributed to the liver and kidneys. Only pyrene absorbed via the lung
and skin has the potential to accumulate in body fat to a significant extent, since the
ingested pyrene will be metabolised in the liver (ACGIH, 2005). These alternative
routes of exposure and metabolism are illustrated in Figure 2.10.
Figure 2.3: Different routes of exposure, distribution and metabolism of pyrene
(ACGIH, 2005)
The half-life for urinary excretion of 1-OHP has been shown to vary in at least three
studies; it was determined to be 18 hours (Buchet et al., 1992), a range of 6–35 hours
(Jongeneelen et al., 1990) and 13 hours (Boogaard & van Sittert, 1994). Taking into
account this variation when developing a biological monitoring protocol, it would be
prudent to follow ACGIH (2005) guidelines, which recommend pre-shift and end-ofwork-week post-shift urine samples for monitoring. In most studies, urine samples
were immediately frozen and kept at –20°C (Jongeneelen et al., 1985, 1988c;
26
Clonfero et al., 1989; Tolos et al., 1990; Boos, Lintelmann, & Kettrup, 1992;
Burgaz, Borm, & Jongeneelen, 1992). Quinlan et al. (1995) reported that 1-OHP in
urine was stable when matched samples were stored at 4°C or –20°C until analysis.
Work undertaken by Boos et al. (1992) indicated that samples were stable for at least
6 months.
The analytical method consists of analysis of urine samples via enzymatic
hydrolysis, sample extraction and purification with a C18 cartridge, reverse-phase
HPLC for separation, and detection with spectrofluorescence (Buckley & Lioy,
1992). The parent compound, pyrene, represents a relatively high proportion of the
higher-molecular-weight occupational airborne PAHs. 1-OHP has been found to be
stable and has only one known precursor, pyrene (Jongeneelen et al., 1988b). One
other important consideration is that there are currently a significant number of
laboratories around the world that are capable of carrying out the analysis required
for the determination of 1-OHP, with many participating in round-robins and quality
assurance testing (R. Geyer, personal communication, 2002).
More recently, there have been studies where alternative biomarkers for exposure to
PAHs have been utilised. Naphthalene was proposed (Rappaport et al., 2004),
utilising its biomarkers 1- and 2-hydroxynaphthalene in urine as an alternative to 1OHP. Naphthalene (with two rings) is present almost entirely in the gaseous phase
and would be a suitable marker for industries where the predominant exposure is
airborne; however, where there is a mixture of dermal and airborne exposure, an
alternative marker correlating better with the higher-number ring compounds could
be more suitable. It is interesting to note that the carcinogenic potency tends to be
greatest among the 4- to 6-ring compounds (ATDSR, 1995).
Another parent-metabolite pairing – BaP and 3-hydroxybenzo[a]pyrene – was the
subject of a study carried out in a selection of industries in France; results showed
this to be a potentially useful method for determining a biological limit marker, as
the parent compound BaP is a known carcinogen (Lafontaine & Gendre, 2003). The
brief report recommended the determination of such a limit by using the French
airborne exposure limit of 150 ng/m3. Again, this assumes that the main level of
27
exposure is via air and may not accurately take into account absorption via other
routes such as dermal and ingestion.
2.3.3 Exposure quantification
There is continued uncertainty about the best method of quantifying exposure and
risk for lung and bladder cancers associated with PAHs. Partially responsible for this
uncertainty is the fact that the mechanisms of action for PAH mixtures are still not
completely known (ACGIH, 2005). Some of the potential pathways include:
1. direct binding to DNA by reactive species to form DNA-PAH adducts;
2. binding to the aryl hydrocarbon (Ah) receptor on cell membranes, with
subsequent signals to the nucleus resulting in changes to the internal cell
milieu; and/or
3. induction of P450 metabolic enzymes, which may then enhance the toxicity
of some components of these mixtures. PAHs are metabolised and
biotransformed through the cytochrome P450 system and are eliminated from
the body mainly through the liver, biliary tract and the excretion of faeces
(Chong, Haines, & Verma, 1989).
In an early study, Dufresne, Lesage and Perrault (1987) found that the strong
adsorption of PAHs onto the surface of some airborne particles, such as coke, can
prevent their determination as BSF, resulting in uncertainty of the true measure of
PAH in air. This adsorption onto particles can also alter their bioavailability and
kinetics in the respiratory tract (Pelfrene, 1976; Gerde et al., 1991). Two NIOSH
health hazard evaluations of PAH exposures in coal-liquefaction processes found no
correlation between BSF and the total level of 29 PAHs analysed (Tolos et al.,
1990).
A significant correlation between PAH concentration in air levels and the resultant
level of 1-OHP in urine has been found in several studies (Jongeneelen et al., 1990;
Tolos et al., 1990; Buchet et al., 1992; Tjoe Ny, Heederik, Kromhout, &
Jongeneelen, 1993; Boogaard & van Sittert, 1994, 1995; Lafontaine, Payan, Delsaut,
28
& Morele, 2000). For this situation to occur, the PAH profile of the workenvironment air would need to remain relatively constant, and contribution from
dermal uptake would have to be minimal. The above studies involved coke plants
and aluminium plants; however, the aluminium plants were sampled on the reduction
lines of a Söderberg plant where the air levels remain relatively constant. Levels in
carbon electrode plants of a prebake smelter would be expected to show a lower
correlation due to the nature of the work. Whilst there is a presence of fume and
airborne particulate in areas such as paste mixing and anode forming, most plants
have invoked mandatory respiratory protection in these operating areas to minimise
inhalation of airborne PAHs. In these plants, dermal contact and uptake is likely to
be a key issue rather than the air content. This has been illustrated by Ferreira et al.
(1994) and Angerer, Mannschreck and Gündel (1997) in graphite electrode plants,
by van Rooij et al. (1992) in the electrode production departments of a prebake
aluminium smelter, and by van Rooij et al. (1993a, 1994a) in a coke oven. Also, the
impact of dermal exposure on the total level would vary depending on the task being
undertaken and most likely in which part of the production process the exposure took
place. Early in the manufacturing of the anode, the paste is mixed at lower
temperatures (160–170°C) and exposure at this point is more likely to include a
greater number of the lower-boiling-point PAHs. There would be less exposure after
the bake cycle where most of the PAH compounds have been driven off at higher
temperatures in excess of 1000°C or in the Söderberg smelter reduction line in which
the higher-boiling-point fraction has been identified.
2.4
Non-occupational exposures
Whilst the measure of total body burden is a useful tool, it must take into account
absorption of PAHs from other sources apart from the occupational environment,
including soaps, shampoos, medicinal balms, food intake and cigarette smoking
(Buratti, Pellegrino, Brambilla, & Colombi, 2000). It has long been known that
tobacco smoking increases the level of 1-OHP in urine, but the relative impact is
dependent on the individual’s other exposures (van Rooij et al., 1994b). In one study,
average daily consumption of approximately 20 cigarettes was required to bring the
levels of 1-OHP in urine to 200 ng/L (Buratti et al., 2000); in another, 30 cigarettes
29
per day resulted in an increase of about 1.0 µg/L (van Rooij et al., 1994b). Levels of
1-OHP in urine did not differ significantly between smokers and non-smokers in a
study by Borak et al. (2002). Variations in the level may be a result of the fractional
retention of PAH in the lungs of the smokers as well as general variation in the rate
of metabolism of the pyrene between individuals. There are also confounding factors
such as the type of tobacco smoked, the tar and pyrene content, whether the cigarette
is filtered or unfiltered, and inhalation practices of the individual.
For low general environmental exposures, the cigarette smoker is likely to have a
more significant increase in 1-OHP level (Jongeneelen et al., 1990; Viau, Carrier,
Vyskocil, & Dodd, 1995); however, at the level in the occupational environment
where the exposure to PAHs is high, it is most likely that the occupational exposure
will overshadow the effects of cigarettes’ contribution (Buratti et al., 2000).
Interestingly, Jongeneelen et al. (1990) and van Schooten et al. (1995) observed that
differences between levels of 1-OHP in urine of smokers and non-smokers were
more pronounced in the most-exposed workers, suggesting the existence of a
synergistic effect of smoking in combination with PAH exposure in the work
environment on the excretion of 1-OHP in urine.
2.5
Biological exposure index
It is one thing to collect sample results for monitoring, but without some form of a
guideline, the results have limited value. Jongeneelen (2001) proposed three
benchmarks for measurements based on 1-OHP levels in urine:
•
•
•
A no observed effect level equivalent to a measurement of 1.4 µmol/mol
creatinine 1-OHP. This is the level below which Buchet et al. (1995)
found no increased level of high frequency – sister chromatid exchanges
(HF-SCE).
The lowest observed level of genotoxic effects indicated by 1.9
µmol/mol creatinine for coke oven workers and 3.8 µmol/mol creatinine
for aluminium plant workers.
A level that equates to the present occupational exposure limits for PACs
(0.2 mg/m3 benzene-soluble matter and/or 2 µg/m3 benzo[a]pyrene
(BaP). The value used is dependent on industry type and pyrene content
of the exposure and is equivalent to 2.3 µmol/mol creatinine for coke
oven workers and 4.9 µmol/mol creatinine for aluminium workers
(Brandt & Watson, 2003).
30
One of the confounders associated with the development of such a guideline is the
variation in the pyrene to BaP ratio in the different blends of coal-tar pitch and the
changes that occur to the product when it is exposed to different temperatures and
conditions as it moves through the different stages of the production process (Brandt,
de Groot, & Blomberg, 1999; Tjoe Ny et al., 1993; Jongeneelen, 2001; Brandt &
Watson, 2003). The ratio of potentially carcinogenic PAHs to pyrene will not remain
constant amongst different CTPV fractions; this marker value will need to be
individually assessed (Bouchard & Viau, 1999).
Exposure limits for the aluminium industry have been calculated (Bouchard & Viau,
1999) by using the TEFs obtained by Krewski et al. (1989) and Collins, Brown,
Dawson and Marty (1991), and the known PAH profile of pyrene and carcinogenic
PAHs in the work environments of interest. This can be readily done for any site if
the above information is known and substituted into the following formula utilising
Jongeneelen’s (1992, 1993) proposed BEI for coke ovens. This is predicated on
linear 1-OHP urinary excretion increases with airborne pyrene concentrations.
ΣBaP
eq
pyrene
c
BEIw = BEIc
ΣBaP
eq
pyrene
w
Where BEIw = BEI in the work environment of interest
BEIc = BEI proposed by Jongeneelen (1992, 1993) for coke oven workers
ΣBaP
eq
pyrene
c
= Sum of BaP equivalents to pyrene airborne concentrations in the
coke plant
ΣBaP
eq
pyrene
w = Sum of BaP equivalents to pyrene airborne concentrations in the
work environment of interest
31
Bouchard et al. (1998) found that relative BEIs can vary up to eight times from one
work environment to another. This is a key element when assessing the potential
risks associated with a particular work environment; a factor of up to eight can have
a significant impact on how the risk is assessed, approached and managed in an
industrial environment. Whilst this variation exists, it can significantly compromise
the value of the test. However, if sufficient monitoring is undertaken over an
extended period of time, it could prove to be of significant value in determining the
presence of trends, particularly after modifications are made to processes or controls.
The American Conference of Governmental Industrial Hygienists, in their BEIdocumentation of PAH (ACGIH, 2005), stated that at present a biological exposure
limit is non-quantifiable and recommended that a level of 1 µg/L 1-OHP (equivalent
to 0.49 µmol/mol cr) should be considered as a post-shift level indicating
occupational exposure to PAH. This level is based on an exposure to PAHs that
would “result in urinary 1-hydroxypyrene levels greater than at least 99% of the
population without occupational or significant environmental exposure” (ACGIH,
2005). This in itself presents a quandary in its application in the industrial
environment. It merely advises that there has been a potential occupational exposure
to PAHs but does not give guidance as to the potential health impact. If not used
correctly, it can cause considerable confusion. Also, it can result in a significant
economic burden on an industry, which may erroneously interpret this as an
exposure limit and attempt to meet this low-level guideline, which is intended for a
different application.
2.6
Biological effect monitoring
As previously discussed, there are currently multiple BEIs being put forward for the
assessment of risk associated with exposure to PAHs in the primary aluminium
industry (Angerer et al., 1997; Jongeneelen, 2001; Lauwerys & Hoet, 2001). Whilst
1-OHP is regarded as a suitable biomarker of exposure to PAHs, there are further
methods currently being investigated to assist with the evaluation of the risk of
cancer. Many PAHs are known to have mutagenic and carcinogenic properties
(Lijinsky, 1991) and, whilst biological monitoring will assist in determining the dose
32
of exposure to PAHs, it may not provide the best indicator of the internally effective
dose, which is the actual level of effect at the target site for carcinogenesis. DNA
adducts arise from the reactions of reactive oxidation products of PAHs with DNA in
various target organs, such as skin, lungs and liver (Brandt & Watson, 2003).
One of the limitations of biological effect monitoring is that many effects cannot be
directly analysed in the target organ/tissue but are necessarily determined in
surrogates that are more easily available, such as blood cells, oral mucosa cells and
exfoliated urothelial cells (van Delft et al., 1998). The metabolic activation of PAH
to reactive metabolites that bind to DNA is a critical event in the initiation of
chemical carcinogenesis (Weyand & Wu, 1994). The development of human cancer
is a multifactorial process requiring several genetic changes in the cell and, as such,
the relationship between biomarkers and cancer has been the subject of several
animal studies focussed on DNA adducts. Some of the markers investigated include
DNA or protein adducts (dell’Omo & Lauwerys, 1993; Haugen, Øvrebø, & Drablos,
1992), cytogenic markers (e.g. micronuclei, chromosomal aberrations, sister
chromatid exchanges) (Tucker & Preston, 1996) and cells with a high frequency of
sister chromatid exchanges. Some of these markers are indicative of an early
biological effect, although it may not be permanent and may not have further
consequences (van Delft et al., 1998).
It is important when selecting a method for exposure monitoring or risk assessment
that the method be relatively user-friendly and readily applied with some form of
target or exposure level. At this stage, biological effect monitoring is complex,
expensive and invasive. Whilst the air and 1-OHP in urine methods do have some
deficiencies, measurements of DNA adducts as yet do not show good correlations
with exposure to PAHs in a variety of workplace and other situations (Hemminki,
1993; Hemminki et al., 1997; Brandt & Watson, 2003). As these methods, and new
methods based on novel chemical markers, are established along with specific
exposure guidelines, the potential for their application in the field may prove
valuable for PAH-exposure risk assessment; however, currently they are not readily
applicable as routine tests.
33
For this study, the analysis procedure chosen must be capable of detecting analytes
arising from PAH exposure via all exposure routes with potential for comparison
with benchmark studies. From the literature reviewed, it is apparent that the most
appropriate methods available for the assessment of exposure to CTPVs (and hence
PAHs) in the primary aluminium reduction industry are:
•
assessments for benzene/cyclohexane-soluble fraction of airborne
contaminants for personal monitoring and static monitoring of the process or
controls, and
•
the determination of 1-OHP in urine to assess the level of total body burden
from the three main exposure routes.
The first of these two methods has been utilised for many years by occupational
hygienists and occupational physicians and compared with exposure limits listed by
both governmental and non-governmental organizations to determine risk. However,
there continues to be uncertainty in the efficacy of the true measure of exposure,
particularly with a compound that has another significant route of entry through the
skin.
2.7
Summary
Exposure to PAHs in aluminium smelting has been formally identified by the IARC
as a carcinogenic health risk to individuals employed in the industry since 1984, with
the known routes of exposure being inhalation, ingestion and skin absorption. To
date, the only accepted forms of exposure monitoring with an associated
occupational exposure level have been related to air exposure with limited emphasis
being placed on the other two routes. From the literature, it is obvious that skin
contact can play a significant role in the total body burden of the individual with this
form of exposure. It is unclear as to whether the methods of assessment and
monitoring regimes in place within aluminium smelting adequately characterise
these exposures or whether the air monitoring correlates with the total body burden
in these areas. Monitoring of both the air and a biological marker should provide the
information necessary to determine if this correlation exists and whether the highest
exposures are in the areas associated with air or skin exposures.
34
3.0 METHODS
This chapter outlines the research methods used to achieve the study objectives listed
in section 1.2.1. After explaining the aluminium plant process, it describes the
exposure groups and study participants, and provides details of air and biological
monitoring sample collection and analysis, and data management and statistical
analysis.
3.1
Introduction
This study utilises air monitoring of PAHs to quantify exposure via the inhalation
route and biological monitoring of 1-OHP to assess total body burden from all routes
of entry. Exposures determined for different sample groups comprised of workers
who undertake tasks in areas of potential PAH exposure in a prebake plant are
compared with published occupational PAH exposure limits and/or guidelines.
Analyses compare results from airborne and biological monitoring to determine if
the outcomes are correlated and whether sampling airborne exposure alone is a true
indicator of total exposure.
The study site was a large prebake smelter in Queensland, Australia. This smelter
produces in excess of 500,000 tonnes of aluminium annually and employs 1250
people. As plant occupational hygienist, the author was primarily involved with the
anticipation/recognition of tasks or areas of potential exposure of employees to
materials that may impact negatively on their health and wellbeing. Where such
situations were expected, monitoring was undertaken of the employee and, in some
instances, the process, to identify areas where controls may be implemented or
improved to eliminate or minimise exposure. This allowed for a high level of
interaction with employees during the assessment process.
Sampling was undertaken across the similar exposure groups (SEGs) over nearly
three years from February 2002 – September 2004. A separate set of post hoc
35
samples was collected over 15 months (March 2005 – June 2006) to assess the
effectiveness of controls implemented as a result of the initial review of data. Each
SEG was monitored at least twice during the three-year period and included a control
group. The size and composition of the SEGs varied.
Ethical approval for the project was granted by the Queensland University of
Technology Human Research Ethics Committee (Ref No 28591/H).
3.2
Study context – plant process description
Aluminium does not occur in the free state in nature and must be extracted from its
oxide (alumina) by an electrolytic process. Alumina has a melting point of 2000°C
and it would be impractical to operate the process at such a temperature. The process
to overcome this, developed simultaneously in 1886 by the French and the
Americans, is referred to as the Hall-Heroult process after the two key developers of
the method. The Hall-Heroult process involves the use of a fluorinated compound of
sodium and aluminium called cryolite, which melts at approximately 1000°C and has
the capability in the molten state to dissolve up to 8% of alumina. At this point it
becomes practical for the application of an electrolysis process. This process is
commonly referred to as the reduction process and is carried out in electrolytic cells
(also known as pots). In the aluminium reduction plant, long rows of pots are
connected in series to form a potline or potroom. Pots generally operate at a current
of approximately 200,000 – 300,000 amps and will produce in the vicinity of 1 tonne
of aluminium per day. This can vary dependent on the technology and the size of the
cells utilised.
Internationally, there are two distinct technologies used for the production of
aluminium – the Söderberg anode process and the prebake anode process. These
processes involve varying configurations of the pots. The four basic types of primary
aluminium reduction technology based on these processes are:
•
centre-break prebake,
•
side-break prebake,
•
vertical-stud Söderberg, and
•
horizontal-stud Söderberg.
36
In the prebake anode cell, the anodes are preformed and baked in a carbon plant
external to the potline. The pots in prebake plants are classified as centre-break
prebake (Figure 3.1) or side-break prebake (Figure 3.2) depending on where the pot
working (crust breaking and alumina addition) takes place.
The anode is made up of pure calcined petroleum coke, which has been ground to a
specific particle size. This is then mixed with a binder, coal-tar pitch, formed into
blocks weighing between 940 and 1200 kg, depending on the reduction technology
being employed, and then baked in a large gas-fired oven at 1250°C, prior to
mounting on aluminium rods for insertion into the electrolytic cell (Figure 3.3).
The carbon anodes are inserted into the pot and replaced as the electrolytic process
consumes them (Figure 3.4). As a result of this prebaking of the anodes, the level of
CTPVs released in the reduction line is significantly lower than in the Söderberg
process. In addition, a centre-break prebake anode cell can be fed alumina without
opening the hood, resulting in a better fume-extraction system allowing fewer
fugitive emissions into the working environment. These are important factors to note
as the majority of the research and epidemiology that led to the IARC classification
was based on work in Söderberg smelters.
Söderberg pots are not prebaked; the paste is dropped into a steel casing hanging
above the pots and is baked on the pot itself by the heat from the molten bath.
Söderberg pots are thus differentiated by the positioning of the current-carrying studs
in the anodes, which may be inserted vertically as in a vertical-stud Söderberg cell
(Figure 3.5) or horizontally in a horizontal-stud Söderberg cell (Figure 3.6). As a
consequence, the resulting emission of CTPV is often significantly higher in the
older-style Söderberg potroom (Figure 3.7).
Collection efficiency of the fumes for this process can operate anywhere between
95% in the best case to 60% in the worst systems, allowing CTPV fumes to escape
into the reduction line environment. Most PAH evaluations have been undertaken
based on this process technology; fewer studies based on prebake technology are
available.
37
Figure 3.1: Centre-break prebake smelter aluminium reduction cell as used in the
smelter in which the study was undertaken (IPAI, 1982)
Figure 3.2: Side-break prebake smelter aluminium reduction cell (IPAI, 1982)
38
Figure 3.3: New anode being installed into a prebake cell showing a typical
configuration of a rod assembly and the carbon block which has been spray-coated
with aluminium
39
Figure 3.4: Consumed anode being removed from a cell in a prebake smelter
reduction line
40
Figure 3.5: Vertical-stud Söderberg aluminium reduction cell (IPAI, 1982)
Figure 3.6: Horizontal-stud Söderberg aluminium reduction cell (IPAI, 1982)
41
Figure 3.7: Vertical-stud Söderberg aluminium smelter reduction line
It should be noted that there are differences between individual plants depending on
age and manufacturer. Some processes are batch-style, allowing for a discrete start
and finish in the manufacturing cycle; others are continuous processes much the
same as a production assembly line. Also, there can be variations in:
•
the temperatures at which the plants operate, hence impacting on where in the
process the different PAHs may volatilise;
•
raw ingredients, e.g. solid pencil pitch or liquid pitch; and
•
the inherent variation in the pitch composition dependent on the source.
The process investigated in this study was a continuous process using liquid pitch
rather than solid pencil pitch hence not requiring a pre-melt section. Pitch
composition was monitored during the investigation, and regular reports were
provided by the pitch supplier to the site and the corporate carbon technical team to
ensure major variations in pitch composition did not occur.
42
3.3
Exposure groups
At the site at which the study was undertaken, the roles of the workers were divided
initially into three groups: anode plant, non-production and reconstruction (Figure
3.8). The anode plant was further subdivided into green carbon and the carbon bake
furnaces (Figure 3.9). Green carbon is that portion of the plant (shaded in green in
Figure 3.9) where the calcined coke and coal-tar pitch are mixed then formed into
anode blocks via a vacuum press and die process, prior to baking. Within the green
plant is a smaller area (shaded in yellow) referred to as the forming area where there
is more potential for exposure to coal-tar pitch and associated volatiles. This is the
area where the ‘forming group’ participants of this study spent the majority of their
time. The blue-shaded area in Figure 3.9 represents the carbon bake furnace where
the formed anodes are baked at high temperatures to achieve the final product. In this
area, large oven pits lined with brick and ceramic fibre are loaded with the carbon
anode blocks. Each anode is transported by overhead crane and placed in layers into
the pit then covered by a layer of coke. The next layer of anodes is placed on top of
the first and also covered with coke and so on until the pit is filled. It is then heated
by natural gas to a temperature of approximately 1200°C for a total of 32 – 48 hours.
This area along with raw materials, the mezzanine floor and the control room are
regarded as the ‘non-forming’ areas of the process.
For this study, qualitative exposure levels were based on the expected levels in
comparison with the occupational exposure limit (OEL) for BSF of 0.2 mg/m3
(ACGIH, 2007); ‘high’ was greater than the OEL, ‘moderate’ was less than the OEL
but greater than 50% of the OEL, and ‘low’ was less than 50% of the OEL.
The shift rotation for the SEGs within the study is based on two 12-hour day shifts
followed by two 12-hour night shifts followed by a four-day break.
43
Anode Plant
Forming
Non-Forming
Former
Technicians
Bake Crane
Operators
Tower
Technicians
Bake Floor
Operators
Non-Production
Reconstruction
Process
Technicians
Bricklayers
Mezzanine
Floor
Technicians
Raw
Materials
Technicians
Controller
Equipment
Technician
(Mechanical)
Equipment
Technician
(Electrical)
Occupational
Health
Human
Resources
Analytical
Laboratory
Figure 3.8: Structure and location of the study’s exposure groups
44
Carbon Anode Plant Process Map
Delivery
Feed
Liquid Pitch
Pitch
Storage
Tank Storage
Transport
to Plant
Tanker Transport
Day Tank
Storage
Tank Storage
Mixing
Paste
Transport/
Anode
Forming
Fume
Treatment
Anode
Cooling/
Storage
Volatiles
200 Degrees
Inject Pitch in
Mixer
200 degrees
160 - 170
Degrees
Paste Transport
Anode Forming
Volatile Deposition
in Ducts
Volatile Collection
in Scrubber
Green Anode
Stacks
Anode Cooling in
Trough
Recycle in Anodes
<100
Degrees
Baking
Anode Loading
Anode Preheating
Anode Baking
End
200 - 600
degrees
Unburnt Volatiles
Carbon Bake
Furnace
Fume
Treatment
ESP Tar
Tar Carry Over to
Scrubber
Tar Collected
Figure 3.9: Carbon anode process within the anode plant. The green-lined area is
regarded as green carbon with the smaller yellow area known as the forming area.
The blue-lined area contains the bake furnace non-forming area.
45
Within the anode plant green area, a production operator rotated through six sets of
role-specific tasks grouped together as:
•
former technician
•
tower technician
•
mezzanine floor technician
•
raw materials technician
•
controller
•
crew leader
An operator was normally assigned to one of these groups for the full four days of
the rotation but could be required to cross tasks depending on staff availability and
process condition. A separate crew that undertook different tasks and did not interact
directly with the green plant operated the carbon bake furnace area of the anode
plant.
As former and tower technicians spend more than 50% of the shift directly exposed
to coal-tar pitch in the early stages of the manufacturing process, they were allocated
to the forming category. Also within the anode plant were electrical and mechanical
equipment technicians who undertook routine and breakdown maintenance on the
former plant. Their exposure varied depending on whether the task took them into
the forming area of the anode plant. To determine their group allocation, equipment
technicians’ work log sheets and sampling sheets were reviewed and a simple
criterion was applied. When an individual spent 50% or more of their shift in the
forming area of the plant, they were allocated to the forming group; if less than 50%
of their time was spent in the forming area, they were allocated to the non-forming
group. Therefore, the anode plant forming group comprised:
•
former technicians
•
tower technicians
•
equipment technicians (>50%)
46
The anode plant non-forming group consisted of the four remaining anode green
plant operator roles, those maintenance technicians whose exposure time was less
than 50% and operators from the carbon anode bake plant:
•
mezzanine floor technicians
•
raw materials technician
•
controller
•
crew leader
•
equipment technicians (<50%)
•
bake crane operators
•
bake floor operators
The reconstruction group, based in a separate location closer to the aluminium
reduction lines, comprised:
•
process technicians
•
bricklayers
The non-production group consisted of personnel from:
•
occupational health team
•
human resources team
•
analytical laboratory
3.3.1 Forming group
The roles of members of the forming group are detailed below. With the exception of
the controller, who would normally spend fewer than 2 hours in the plant, the roles
require operators to be in the plant environment for approximately 10 hours per shift.
3.3.1.1 Former technician
The role of former technician involves tasks such as manual measuring, cleaning,
fault rectification, and quality and equipment checking. These tasks occur in the
early part of the anode manufacturing process when the paste is mixed and ‘formed’
into anodes prior to the baking process. This may involve interaction with the anode
47
paste mixing, movement of the paste along the conveyor belt system, and the process
of injecting the paste into the vacuum former where the anode shapes are moulded.
Also, there is interaction with the paste when blockages occur, particularly in
relation to the former vibration plate. In this task, hot paste is fed down a chute to a
vibrating plate for distribution to the anode vacuum former. On occasion, the paste is
not evenly distributed and can result in a blockage requiring attention of the former
technician. The lid of the plate is lifted to obtain access and a long spatula-type tool
is used to clear the blockage of the hot paste. This task can take from 2 – 10 minutes
to complete. Another area for potential exposure to the paste is during the cleaning
of some of the equipment. Here the technician must clear away any gross
contamination of paste adhering to the equipment prior to hand over to the
maintenance team. As a result, the former technician’s role has the highest contact
level with ‘green’ anode paste material. Green material is a term used to indicate that
the pitch/coke mixture has not been baked.
3.3.1.2 Tower technician
Of the green carbon operators, the role of tower technician covers the widest area of
the plant. The role may require sampling, equipment checks, cleaning and fault
rectification on any of the 10 levels of the green carbon process building. There is
potential contact with pitch-contaminated raw materials and fume and airborne dust
associated with the petroleum coke. The tower technician’s level of exposure to pitch
material is expected to be lower than that of the former technician, but higher than
other technicians. Exposure has the potential to increase when assisting the former
technician with cleaning tasks around the paste mixers, conveyer belts and former.
3.3.1.3 Equipment technician
Mechanical
The mechanical equipment technician role is one of maintenance in the anode
forming plant. This involves interaction with all pieces of the equipment at one time
or another. The equipment technician team is made up predominantly of mechanical
fitters who are required to undertake preventative and breakdown maintenance on
the equipment. Contact with pitch-contaminated equipment is a regular occurrence;
the level of contamination will vary depending on the state of machinery when the
48
work is carried out and whether the work is undertaken in the plant or the workshop.
As the study site is a continuous-process plant rather than a batch plant, breakdown
maintenance usually results in higher exposures as less time is available to
completely clean down prior to undertaking repairs. The mechanical equipment
technician’s time in the plant varies depending on the tasks, but would generally
involve working on equipment for at least 8 hours of the 12-hour shift; exposure is
expected to be moderate to high.
Electrical
The electrical equipment technician role is similar to its mechanical equivalent,
involving varying levels of interaction with equipment during breakdown and
preventative maintenance. Because the nature of the work concentrates on electrical
components, which tend to be less heavily coated with coal-tar pitch and associated
product, it is likely to result in lower exposure to pitch compounds; exposure is
normally fewer than 8 hours per day.
3.3.2 Non-forming group
3.3.2.1 Mezzanine floor technician
The mezzanine floor technician’s exposure is predominately associated with the
cleaning and processing of ‘spent’ anodes, i.e. anodes that have been returned from
the reduction lines after use. These anodes are cleaned via an automated shot-blaster
followed by some manual intervention using small jackhammers or ‘scabble guns.’
The anodes are then crushed in a butts-thimble press, and the resulting product used
as a portion of one of the raw material streams in the new anodes. As returned
anodes have been baked and have spent time in the reduction cell, unless mezzanine
floor technicians are requested to assist in one of the other technician roles, their
exposure to pitch materials and volatiles is minimal.
3.3.2.2 Raw materials technician
The raw materials technician is responsible for maintaining material levels of green
scrap and used butts in the process. This requires the operation of loaders, forklifts
and trucks within the bunker areas, crushing plant and ‘green’ scrap sheds. The term
‘green carbon’ is used to refer to carbon paste or block that has not been baked in the
49
furnace ovens and hence levels of PAHs are higher. Exposure occurs during
handling of the green scrap. The raw materials technician also assists the general
green carbon team in the other roles. Exposure to pitch is expected to be low to
moderate.
3.3.2.3 Controller
The controller monitors the process from the main control room in the green carbon
building. Under normal circumstances, the controller would not be involved in work
outside of this area; exposure to pitch is likely to be very low.
3.3.2.4 Crew leader
The crew leader co-ordinates and manages the shift team comprised of the controller,
and former, tower, mezzanine and raw materials technicians. The crew leader is
required to move throughout the plant to ensure all processes are functioning
correctly. Under most circumstances, exposure is limited to the ambient fume levels
within the plant, but there are occasions when the crew leader participates in duties
resulting in greater exposure. When this occurred during the study, log sheet details
were reviewed and the appropriate group allocation was made based on the same
criterion used for equipment technicians (section 3.3.1.3).
3.3.2.5 Bake crane operator
The bake furnace crane operator role involves placement of ‘green’ anode blocks
into the bake furnace pit utilising large overhead cranes such as those illustrated in
Figure 3.10. A green anode is one that has been formed into shape but is yet to go
through the final baking process. The crane cabins are air conditioned and normally
sealed; however, the integrity of the seals can deteriorate between maintenance
services, which can impact on the potential for exposure. Exposure to pitch is
expected to be low to moderate during the shift. Operators generally spend 8 – 10
hours in the crane.
50
Figure 3.10: Carbon bake crane lowering green anodes into the bake furnace pit
3.3.2.6 Bake floor operator
Bake floor operator duties, associated with operation and maintenance of the
furnaces, include monitoring and relocating furnace burners, draft fans and
associated ancillary equipment; management of tar from the electrostatic
precipitators; on occasion, breaking up reject anodes for recycling into the process;
and general housekeeping duties around the bake furnace. Exposure to pitch is
expected to be low to moderate during the shift. Operators generally spend 8 – 10
hours in the bake furnace building or in the immediate surrounds.
3.3.3 Reconstruction group
The reconstruction team’s role is the rebuilding of reduction cells once they have
been removed from service. The average life of a reduction cell used at the smelter in
the study is approximately 1800 days. The cell-rebuilding process involves four
stages:
•
clean out of the old cell
51
•
structural steel repairs
•
refractory replacement
•
carbon cathode replacement
− paste preparation
− paste transfer
− paste loading
− Brochet machine ramming
− hand ramming
3.3.3.1 Process technician
Reconstruction process technicians undertake carbon cathode replacement tasks and
therefore have the greatest potential for exposure to PAHs in this group, as the paste
used contains coal-tar pitch. The task of ramming involves forcing the paste into the
crevices of the cathode to ensure there are no gaps where the molten aluminium may
collect. Much of the ramming is carried out using a mechanical rammer, called a
Brochet machine (Figure 3.11), but some hand ramming (Figure 3.12) is also carried
out. Whilst the paste may be used warm or cold in the process, cold-paste ramming
is used on the study site. In recent years, the level of exposure during these tasks has
been reduced by the introduction of cold paste and some mechanisation, but there is
still potential for exposure during paste preparation and hand ramming. Also, there is
a task that involves the painting of liquid pitch on the carbon cathode block prior to
ramming, to improve the adhesion of the ramming process, which has the potential
to increase exposure. Neverteheless, exposure levels are expected to be lower than
for those tasks in the employee groups that involve working with coal-tar pitch at
temperatures above 100°C. Workers generally spend 8 – 10 hours in the areas where
exposure is most likely. The level of the exposure is expected to vary from low to
moderate depending on the task; brick-working tasks is likely to be in the lower
region with ramming tasks in the moderate range.
52
Figure 3.11: Mechanical ramming of paste into the joints between the carbon blocks
of the cathode using a Brochet machine
Figure 3.12: Ramming of paste into side-wall join using hand rammers
53
3.3.3.2 Bricklayer
Tasks associated with the bricklayer role are less likely to bring these workers into
direct contact with coal-tar pitch or its products. The main bricklayer task is to line
the steel shell with refractory bricks onto which the carbon blocks that make up the
cathode will later be placed. As the bricklayers work in the same area as the process
technicians and it is not unusual to have the two groups working on adjacent shells,
there is potential for exposure resulting from fumes from the adjacent shell. While
the level of exposure is expected to be lower for bricklayers than process technicians,
generally they also spend 8 - 10 hours in the area.
3.3.4 Non-production group
Non-production personnel from the occupational health team, the human resources
team and the site laboratory were used as controls for the 1-OHP monitoring in this
study. During the period of participation, none of these personnel were involved in
any tasks associated with exposure to coal-tar pitch; no exposure is expected.
3.3.5 Exposure profile
Except for the non-production group, the SEGs have the potential for significantly
varying exposures depending on the task and location. This is indicated in Figure
3.13 by the positioning of groups across boundaries between exposure levels.
54
HIGH
Anode Plant Forming
MODERATE
Reconstruction
t
LOW
Anode Plant Non-Forming
Non-Production
Figure 3.13: Potential exposure levels of SEGs
3.3.6 Personal protective equipment
Respiratory PPE was mandatory in all areas where there was a potential exposure to
airborne PAHs, such as in the forming area of the anode plant and in the cell during
paste ramming and pitch painting. All individuals having the need for a respirator
were trained in the use and maintenance of their respirator and were required to
undergo a quantitative face-fit test. Quantitative face fitting of the respirators utilises
a method based on the comparison of particle counts taken simultaneously inside and
outside of the respirator when worn, providing an accurate measure of the face seal
of the respirator for the individual. This information is then used in the selection of
the respirator best suited for that individual. There was some variation in the type
and level of protection provided, i.e. full-face or half-face mask respirators. Wearing
of respiratory protection in the non-forming areas of the anode plant was task based
and not mandated. Long-sleeved cotton drill shirts, long trousers, a cotton balaclava
55
(optional) and leather ‘riggers’ gloves were normally worn when working with coaltar pitch paste (Figure 3.14). Also, disposable coveralls were utilised in the
reconstruction area when liquid pitch was painted onto the walls of the cell. If the
exposure to PAHs is via inhalation, a correctly worn respirator should prevent
exposure, and the level of 1-OHP in urine will not be elevated.
.Figure 3.14: Clothing and PPE worn for working with coal-tar pitch paste
3.4
Recruitment of study participants
Initially, a presentation was made by the author and the site’s medical officer to the
site’s senior management team to outline the context and purpose of the monitoring
and the value of being able to characterise PAH exposures that were not necessarily
associated with airborne exposures. With the full support of the leadership team,
further presentations were made to each of the work groups in the areas of the
proposed investigation, outlining the study, the monitoring to be undertaken and
56
requesting volunteers. A copy of the presentation is located in Appendix 1. Personal
monitoring at the smelter has been undertaken on a routine basis for more than 20
years and, whilst it is not compulsory, all workers are encouraged to become
involved. From Table 3.1 it can be seen that the response rate was very positive, with
participation ranging from a high level (96%) in the monitoring program for the
anode plant forming production operators to a lower level (65%) in the
reconstruction group bricklayers. The lowest level of participation (50%) was for
analytical laboratory and human resources personnel in the non-production group,
These people worked in locations where they would not be expected to be exposed to
PAHs. All participants were asked to sign a consent form (Appendix 2) at the
beginning of the study and a ‘permission to sample’ authorisation form prior to each
sample collection.
Table 3.1: Number of study participants and % participation
Sample group
Size of group
(N)
Participation
(n) (%)
Forming production operators
25
24 96
Non-forming production operators
24
21 86
Equipment technicians
27
24 88
Process technicians
19
15 80
Bricklayers
20
13 65
Analytical Laboratory
12
6 50
Occupational Health
10
7 71
Human Resources
8
4 50
Anode plant
Reconstruction
Non-production
3.4.1 Sample size calculations
Calculations to ensure that the available sample sizes would be sufficient to test the
project hypotheses had to address two important limitations. Due to the size of the
plant in which the study was undertaken, there was a logistical maximum number of
57
staff who could be utilised. An additional consideration was the cost of analyses as
the tests undertaken were quite expensive. Calculations to determine how these
constraints would impact on the sample size for a viable study were performed based
on preliminary monitoring results. The sample size requirements varied depending
on the range of the standard deviation of the sample group and the difference in
means between the two sample groups being compared. Table 3.2 shows data
obtained from the initial sample runs on which the power and sample size
calculations were based. The initial set of sampling results were assessed for
normality against the Anderson-Darling test and found not to be normally
distributed. To carry out the power and sample size calculations, Minitab V14.0
software was employed utilising the power and sample size function. An α of 0.05
was used in the two-tailed calculations. Using the data from Table 3.3, comparing
the anode plant in general and the reconstruction plant using a difference of 8.22, the
sample sizes to achieve a power of 0.90 were calculated to be 37 for each group. For
the comparison of the forming plant and reconstruction and non-forming groups with
a difference of 11.6, the size of each group was calculated to be 21.
Table 3.2: Data for power and sample size calculations for the various SEGs
Anode Plant
Forming
Anode Plant
Non-Forming
Reconstruction
No. Samples
Total
Anode
Plant
33
22
11
13
Post-shift 1-OHP results
(µmol/mol cr) Means
9.42
13.3
1.64
1.2
SD
10.67
11.17
1.59
0.81
3.5
Exposure monitoring
3.5.1 Airborne exposure monitoring
Historically, exposure monitoring has involved the airborne monitoring of
particulates and fumes of the process or absorption by the individual. These results
58
are then related to occupational exposure limits as set by bodies such as the
American Conference of Governmental Industrial Hygienists (ACGIH) in the United
States and the Health and Safety Executive in the United Kingdom. This may then be
evaluated in comparison to known exposure guidelines and, where necessary,
controls established.
3.5.1.1 Stationary monitoring of the process
Whilst stationary (static) monitoring is not used for direct comparison against
occupational exposure standards, it is generally utilised to monitor a process to
assess the controls in place and identify potential areas of fugitive emissions. It was
used in this study to obtain the levels of PAHs being emitted from the processes in
areas of the plant where the reconstruction of the cells is undertaken and in the anode
production plant. High levels of fugitive emissions from a particular section of the
process or a piece of equipment can provide valuable information in relation to the
potential exposure profile and working habits of the individuals undertaking
activities in and around the area. This information was used in the analyses to
determine whether there were any relationships associated with the airborne levels at
specific locations in the workplace, the personal monitoring of the individual and
lastly the biological monitoring.
A sample head and pump is located in one position for the duration of the monitoring
period. As this is not a true representation of the exposure of an individual who
would normally be moving, the results cannot be compared with occupational
exposure limits. Stationary monitoring was carried out according to NIOSH method
5042 (Schlecht & O’Connor, 2003). Sampling was carried out using a PTFE
laminated membrane, 2-µm pore size, 37 mm diameter Zefluor pre-filter, backed by a
37 mm diameter cellulose support pad in a cassette filter holder. The filter heads were
attached to a SKC PCXR4, SKC PCXR8 or Aircheck personal monitoring pump
(SKC Inc., Pennsylvania, USA) set at 2 L/min (Figure 3.15).
59
Figure 3.15: Monitoring pump and sample train configuration for NIOSH method 5042
Sampling locations were selected after discussions with plant employees and
inspection of the process. Pumps were positioned in the work environment contained
in a protective case with plastic Tygon® tubing connected to the pump inlet and run
inside a PVC pipe up to the filter head at a height of 1.5 m above the ground (Figure
3.16). Locations selected were perceived to be areas of significant exposure or
concern and accessed by technicians during the undertaking of their tasks. Each
sample was run for 10 - 12 hours. After sampling, the sampling head was removed
and the two plastic plugs were installed in the open ends of the cassette. At this
stage, pre- and post-flow calibrations, exposure times and sampling details were
added to the sample log sheet.
Glass fibre filters were handled only when necessary and with clean tweezers at all
times. Each sample head was uniquely labelled then wrapped in aluminium foil or
placed in an opaque container to protect the sample from light.
60
At least one field blank was submitted with each set of samples containing up to 10
samples and an additional blank for each subsequent 10 samples. Blanks were
handled in the same manner as other samples except that no air was drawn through
them. At this point, the appropriate custody documents were completed, and the
samples were sent by secure courier for analysis by BHP Environmental Health
Laboratories at the Port Kembla Steelworks site, New South Wales. The results were
used to develop a profile of the plant. Sample locations for the green carbon plant
were:
•
Integrated Paste Plant 6th Floor Centre Beam
•
Integrated Paste Plant 6th Floor south west Corner
•
Control Room
•
L1&2 Mixer Bottom right hand side
•
L1&2 Mixer Top left hand side
•
L1&2 Preheat
•
L1&2 Vibro Paste Feeder
•
L3 Mixer Bottom hand side
•
L3 Mixer Top left hand side
•
L3 Paste Belt
•
L3 Preheat East End
•
L3 Preheat Magnetic Separator
•
Pitch Day Tank
•
Tail End 501 Conveyor Belt, Back
•
Tail End 501 Conveyor Belt, Front
•
Between Anode Former Lines 1 & 2 and Anode Former Line 3
Figures 3.17 and 3.18 show locations of sample points in the carbon bake area and
Figure 3.19 shows locations in the cell-reconstruction building.
61
Figure 3.16: Static sample pump setup in the green carbon paste area on the 6th floor
of the anode plant
22
30
40
10
33
43
56
4
7
2
3
6
9
10
8
1
5
Figure 3.17: Carbon bake furnace for reduction lines 1 & 2; locations of static samples
1
8
2
4
1
2
9
6
11
12
10
lower
level
3
lower level
near stairs
1
5
7
8
Figure 3.18: Carbon bake furnace for reduction line 3; locations of static samples
62
Figure 3.19: Cell-reconstruction site static sample locations
Figure 3.20: Monitoring pump and sample train configuration with XAD tube for
NIOSH method 5515
Where there was a potential for vapours and gases, a resin-filled sorbent tube was
connected in series after the filter (Figure 3.20) as per NIOSH method 5515
(Schlecht & O’Connor, 2003) to determine what level of fume and volatiles
63
contributed to the sample and the characterisation of that fume (this is the main
difference between NIOSH methods 5042 and 5515). Previous studies (Jessep, 2007;
Tjoe Ny, 1993) at aluminium smelters have indicated that there was no gaseous
phase PAHs of the 4-6 ring structure detected in the sorbent tubes of the sampling
train. Monitoring undertaken in an earlier study at this site (Clarke. 2001) also
returned the same result. In the initial stages of this monitoring program this method
was repeated and again levels of PAHs from the resin-filled tubes were below the
level of detection (<0.05µg); hence the results were reported as total BSF rather than
differentiating between particulate, fume and vapour. Whilst this approach can limit
the ability to differentiate between the different phases and may impact on the
control approach taken where the vapour phase is a significant component, the small
proportion of the gaseous phase in this case was not regarded as a major issue for
this study. As there were no PAHs detected in the sorbent tubes in the initial
samples, NIOSH method 5042 was adopted for the analysis during the remainder of
the project. A series of samples using NIOSH method 5515 were run towards the end
of the sampling exercise as a check, and again nothing was detected in the sorbent
tubes. On completion of the monitoring, the filter heads were wrapped in aluminium
foil and forwarded to the analytical laboratory for analysis. This analysis method is
detailed in section 3.5.1.4.
3.5.1.2 Occupational monitoring of workers
Each SEG was monitored. Wherever possible, personal air monitoring samples were
allocated to coincide with the biological monitoring. Participants were asked to
report to the Occupational Hygiene Laboratory prior to commencement of their shift
to be fitted with a personal monitor. The configuration and method used was the
same as that for the static monitoring except that the pumps were worn by the
individuals and the sampling head was positioned in the individual’s breathing zone,
which is a 300 mm hemispherical region about the nose and mouth (Figure 3.13).
The cassette was attached to the sampling pump with plastic Tygon® tubing so that
the glass fibre filters in the sampling cassette were exposed directly to the
atmosphere. The sampler was attached vertically in the worker's breathing zone in
64
such a manner that it did not impede work performance. The sampling device was
protected from direct sunlight.
Figure 3.21: The 300 mm hemispherical breathing zone for positioning of the personal
sampling head (Victorian Workcover Authority, 2000)
3.5.1.3 Pre-shift briefing and daily work log
At the beginning of each shift when the personal monitor was worn, each participant
was briefed in relation to the monitoring process and what to do in case of pump or
sample head malfunction. Personal details were recorded on a monitoring sheet, and
each participant was asked to record tasks and other pertinent details of his/her role
on a daily work log during the shift (Appendix 3). On completion of the shift, the
65
participant returned to the laboratory where the monitor was removed, flow details
were recorded and the log sheet filed in a secure location. Each sample was uniquely
labelled and sent to a NATA-certified analytical laboratory for analysis. The data
collected were used to develop a profile for each exposure group.
3.5.1.4 Analysis of air monitoring
Analyses of the air samples (both personal and stationary) were undertaken at BHP
Environmental Health Laboratories (EHL) at the Port Kembla Steelworks site. The
same analysis method was used for both. The method for the determination of BSF
was in-house method EHL 3 based on the Occupational Safety and Health Authority
method 58 (OSHA, 1986). Air samples submitted for analysis were collected by
drawing known amounts of air through cassettes containing pre-weighed glass fibre
filters as per NIOSH methods 5515 and 5042 (Schlecht & O’Connor, 2003).
The absolute detection limit is defined in the OSHA method as 0.006 mg on the
filter. As the method subdivides the extract in two, the lowest detectable mass is
0.003 mg. The precision determined at a filter loading of 0.207 mg was 16.2%. At
the limit of quantitation of 0.033 mg the precision was ±25% or better. The accuracy
of the method was determined by recovery of coal tar from spiked filters and found
to be 89.4%. Unexposed glass fibre or Teflon filters, taken from the batch used for
collection, were processed as system blanks in triplicate. If one blank was seen to be
different from the other two, it was considered an outlier if its value differed by more
than 50% of the mean of the two closer results. If all three results differed widely,
the triplicate blank measurement was repeated. The means of the three results (after
rejecting outliers) were used in calculations. Briefly the procedure followed was:
•
Immediately prior to analysis, the description of the filter was noted
particularly in relation to odour, colour and loading.
•
2 mL Teflon cups were placed in a vacuum oven set at 40°C and –40kPa
pressure for 1 h. An extra Teflon cup was included as a blank check weight.
•
Cups were allowed to cool in a desiccator for 10 – 15 min then equilibrate at
room temperature.
•
Each cup was passed over a static eliminator, weighed to within 0.001 mg
and the weight was recorded.
66
•
Each filter was removed from its cassette, folded into quarters (sampling
surface inside) and placed into correspondingly labelled 4 mL glass vials
using flat-tipped stainless steel tweezers. To avoid losing any particulate
material, the inside of the cassette was wiped with the folded filter paper.
•
1.5 mL of benzene was added to each sample in the vial, tightly capped and
vibrated in an ultrasonic bath for 1 h.
•
Solutions were filtered through Pasteur pipettes containing a 1 cm piece of
glass fibre filter. A pipette filler was used to push the solution through to a
labelled 2 mL glass vial which was immediately capped.
•
A 1 mL graduated syringe was used to deliver exactly half of the original
extraction volume used to the separate weighed Teflon cups, which were then
placed in the vacuum oven for 2 h at 40°C and –40kPa pressure. After this
time, the vacuum pump was turned off, the vent valve was closed and the
cups were left in the oven for a further 1 h at 40°C.
•
Sample cups were removed from the oven and placed in a desiccator for a
minimum of 10 min, then equilibrated at room temperature.
•
Each cup was passed over a static eliminator and re-weighed to within 0.001
mg.
If the BSF result exceeded the appropriate exposure limit, the sample could be
further analysed by HPLC with a fluorescence or ultraviolet (UV) detector. This
allowed the determination of the presence of selected PAHs (Table 3.3).
In the early stages of the investigation, the sampling process was undertaken as per
NIOSH method 5515 (Schlecht & O’Connor, 2003) and involved a sorbent tube after
the filter (as described in section 3.5.1.1) to characterise the presence and type of
fume. Desorption of the PAHs from the sorbent contained in the glass tube was
carried out according to the following procedure.
•
The front glass wool plug and front sorbent section were transferred to one
culture tube with the back sorbent section and the middle glass wool plug
placed into a second culture tube. Acetone was added to each culture tube;
tubes were capped and allowed to stand for 30 min, swirled occasionally.
67
•
The solution was filtered through a 0.45 µm membrane filter and prepared for
analysis via gas chromatography, using a 30 m x 0.32 mm ID, fused silica
capillary column.
•
Temperature at the injector head was set at 200°C with the flame ionisation
detector (FID) temperature set at 250°C. The temperature program was set to
130°C ramping up to 290°C at 4°C/min.
•
Carrier gas was pre-purified helium flowing at a rate of 1 mL/min with
further helium makeup at 20 mL/min. Hydrogen gas was used as the fuel for
the FID.
•
Calibration graphs of peak area versus µg of each PAH per sample were
prepared for the calculations.
•
The limit of detection for this method was 0.3 – 0.5 µg per sample.
•
The sample aliquot was injected into the sample port and the temperature
program started. Results were provided via a graph from which retention
times and the areas under the peaks were calculated. If the peak area was
above the calibration range, the sample was diluted with appropriate solvent,
re-analysed and the appropriate dilution factor applied in calculations. The
substances analysed are detailed in Table 3.3
Calibration graphs were used to calculate the concentration in air via the mass (µg)
of each analyte found on the:
•
filter (W),
•
front sorbent (Wf),
•
back sorbent (Wb) sections,
•
average media blank filter (B),
•
front sorbent (Bf) and
•
back sorbent (Bb) sections.
68
Table 3.3: Average levels* of PAH compounds in air monitoring in anode plant green
carbon assessed by gas chromatography (Method 5515 in NIOSH, 1994)
*Based on 100 static air samples.
Compound
Synonym
Average level
µg/m3
acenaphthene
4.56
acenaphthylene
0.07
anthracene
0.83
benz[a]anthracene
1,2-benzanthracene
benzo[b]phenanthrene
1.14
Benzo[A]fluorene
0.28
Benzo(B)fluorene
0.14
benzo[b]fluoranthene
3,4-benzofluoranthene
2,3-benzofluoranthene
benz[e]acephenanthrylene
1.06
benzo[k]fluoranthene
11,12-benzofluoranthene
0.86
benzo[g,h,i]perylene
1,12-benzoperylene
0.50
benzo[a]pyrene
3,4-benzopyrene
6,7-benzopyrene
0.82
benzo[e]pyrene
1,2-benzopyrene
4,5-benzopyrene
0.68
chrysene
1,2-benzophenanthrene
benzo[a]phenanthrene
1.13
dibenz[a,h]anthracene
1,2,5,6-dibenzanthracene
0.25
Dienzopyrene Isomers
0.34
fluoranthene
benzo[jk]fluorene
2.17
fluorene
o-biphenylenemethane
1.80
indeno[1,2,3-c,d]pyrene
2,3-phenylenepyrene
0.56
naphthalene
naphthene
4.64
phenanthrene
pyrene
5.45
benzo[def]phenanthrene
1.74
69
The concentration, C (mg/m3), in air as the sum of the particulate concentration and
the vapour concentration was calculated using the actual air volume sampled, V (L),
utilizing equation 3.1:
C = (W-B+W f+W b-Bf-Bb) mg/m
3
Eq 3.1
V
3.5.2 Biological marker monitoring
Each of the similar exposure groups outlined in section 3.3 was studied by
monitoring the level of 1-OHP, a metabolite of pyrene excreted in the urine of
individuals exposed to pyrene. As pyrene is a ubiquitous component of PAH
compound groups, it has been utilised as a surrogate marker for other PAH
compounds.
3.5.2.1 Biological sample collection
As described in section 2.3.2, the half-life for urinary excretion of 1-OHP has been
shown to vary in at least three studies. Taking into account this variation, ACGIH
(2005) guidelines for biological monitoring were adopted; these recommend preshift and end-of-work-week post-shift spot urine samples for monitoring with urinary
creatinine levels between 0.3 g/L and 3.0 g/L.
On the shift prior to the sampling shift, each participant was provided with a
sampling pack containing:
•
sample jars,
•
biological hazard bags,
•
work log, and
•
questionnaire and instructions (Figure 3.22).
70
Figure 3.22: Contents of the 1-OHP in urine sampling kit provided to study
participants at the beginning of each sample run
Participants were asked to provide two containers with samples of mid-stream urine
prior to the commencement of their first shift of the next rotation.
Sample jars were placed in a biological hazard sample bag and then in a labelled,
designated container in the laboratory freezer; they were collected the following day
and relocated to the medical centre freezer. The same process was followed
immediately following the last shift of the rotation. The pre- and post-shift samples
were uniquely labelled and sent to the NATA-certified Workcover NSW Chemical
Analysis Branch for analysis along with the control samples.
The analysis method used at the analytical laboratory was based on the method first
described by Jongeneelen et al. (1987), then Tolos, Lowry and MacKenzie (1989)
and Hansen, Poulsen, Christensen and Hansen (1993). All samples were analysed by
Workcover NSW Chemical Analysis Branch utilising method WCA158 (Workcover
NSW, 2005). Briefly, duplicate urine samples were adjusted to pH 5.0 with acetic
71
acid. An acetate buffer was added, followed by β-glucuronidase. The mixture was
then heated for 3 h in a water bath at 60ºC to hydrolyse the glucuronide and sulphate
conjugates (Figure 3.23). A 50 µL sample was injected into C18 Solid Phase
Extracting column with a mobile phase of methanol:water to isolate the analyte, 1OHP. Cleaned extracts were analysed by HPLC with fluorescence detection with an
excitation wavelength of 242 nm and an emission wavelength of 388 nm. The
method has a detection limit of 0.5 µg/L.
H OOC
HO
O
O
Enzyme
OH
OH
OH
β -D-G lucur onide
1-Hydroxypyrene
Figure 3.23: Enzymatic development of the metabolite 1-OHP
Results were reported as µg/L 1-OHP and the creatinine value was determined. The
creatinine (cr) value was used to correct for variations arising from urine dilution.
Results were finally reported as µmol/mol cr.
As part of the sampling protocol, samples were also collected from a control group
whose numbers were not involved in production roles and hence were not exposed to
CTPV. All results for this group had levels below the level of detection of the
method of analysis.
3.5.2.2 Combined sampling
To assess whether there was a correlation between the level of 1-OHP in urine and
personal monitoring of BSF in the air, combined sampling was undertaken on 58
occasions. During this process, participants were required to wear a personal airsampling pump during the same shift rotation they were tested for 1-OHP.
72
3.5.2.3 Potential confounders
Prior to providing a urine sample, each participant completed a self-administered
questionnaire (Appendix 4). This was introduced to collect data in relation to
potential sources of exposure that might confound the relationship between the air
and the urine measures. There are several possible confounders that may impact in
varying degrees on the results including:
•
Exposures during the 48 hours prior to monitoring, such as non-occupational
use of creosote, burning off or natural bush fires, and use of tar-based skin
products or shampoos. Whilst these may noticeably impact on the levels of 1OHP in the urine samples of non-occupationally exposed individuals, as
discussed in section 2.4, these levels would not be of concern in the
occupationally exposed group of this study.
•
Potential food sources of PAHs were assessed as these have been known to
elevate the 1-OHP levels in urine; however, from the literature search
(section 2.1.2), it would appear unlikely that these were significant enough to
impact on the measurement of occupational exposures.
•
Smoking habits were targeted, as the literature review indicated a potential
elevation of 1-OHP in urine due to inhalation of cigarette smoke. As in the
case of food intake, it was not expected to impact significantly on
occupationally acquired levels of pyrene (see section 2.4).
•
PPE was mandatory in all areas where there was a potential exposure to
PAHs. There was some variation in the type and level of protection provided,
i.e. full-face or half-face mask respirators. Wearing of respiratory protection
in the carbon bake furnaces was task-based. Also, disposable coveralls and
impermeable gloves were implemented towards the latter stages of the
project as one of many additional controls as part of a process intervention
strategy.
•
Also of interest were potential elevated exposures from previous
unmonitored shifts due to 1-OHP which may not have been fully excreted.
Prior to the commencement of each monitored shift, the participant was
asked to provide details of any potential high exposures in the two work
shifts immediately prior on the questionnaire submitted with the urine
sample. This information was transferred to a spreadsheet that could be
73
referenced if elevated pre-shift samples were identified. The potential impact
on the final 1-OHP result was addressed by using the difference between preshift and post-shift results as one of the variables instead of only the postshift result. Buchet et al. (1992) reported that there was not a significant
difference when expressing 1-OHP urine excretion as the change over the
work shift instead of post-shift value alone.
•
A potential variation in the ratio of pyrene to BaP in different suppliers’ coaltar pitch formulations can impact on the level of 1-OHP. Obviously, pitches
with higher pyrene ratios will result in more 1-OHP being metabolised and
hence a higher result. Therefore, it was important to note if there were any
trials of different pitches being undertaken during the study. Review of site
records and discussions with green carbon workers indicated that no pitch
trials were undertaken during the periods of the study when sampling was
undertaken.
•
Individual behavioural characteristics can significantly impact on the results
(‘dirty worker effect’). An individual who is more prone to come in contact
with the pitch due to the way s/he works, or does not wash as frequently or
uses PPE incorrectly can introduce additional variation into the analysis. This
can be a difficult aspect to address, as a decision must be made as to whether
the elevation in results is specifically due to the individual’s behaviour. To be
able to confirm this with a degree of confidence would require multiple
sampling of individuals over an extended period of time. As no individuals
were sampled more than three times during the study, there are insufficient
data available to undertake this assessment. Hence, interpretation of results
will need to assume the effect is not significant enough to impact on this
occasion, but will acknowledge this particular limitation.
3.5.2.4 Participant communication
Feedback sessions were held on a regular basis to outline the general group results
obtained, and each participant was given the option of viewing his/her personal
results by contacting the author as the project leader or the site’s Principal Medical
Officer.
74
3.6
Data management and statistical analysis
Quantitative data collected were entered into Microsoft Excel for Windows for initial
review, with further descriptive data analysis carried out via a selection of statistical
tools utilising a commercial statistics software package called Minitab®. Variables
were based on the different monitoring measures for the work groups and areas
being investigated as outlined in section 3.3. These were:
•
static sampling results of the specific work areas,
•
personal air sampling results of SEGs in these areas and
•
biological monitoring results of SEGs in these areas.
For the latter group, data were presented in three forms, pre-shift result, post-shift
result and a difference result. The difference variable was obtained by subtracting the
pre-shift from the post-shift result to remove any potential effect of the pre-shift
loading of 1-OHP.
Results were assessed for normality to determine whether parametric or nonparametric analysis would be utilised. In the first instance, the Anderson-Darling
normality test within the Minitab® statistical program was utilised. This approach
was initially chosen as it was the most commonly used test for this purpose within
the aluminium industry where this project was undertaken. The results of this
analysis showed that only one of the 34 sets of variables was normally distributed.
As a consequence, transformation of the data was undertaken. Different
transformations may be used depending on the condition of the original data. For
example, for positively skewed data either a square root or logarithmic approach is
best; however, if the data tend more to the lognormal distribution or display a
standard deviation proportional to the mean, then a logarithmic approach is
preferred. In the case of negatively skewed data, squaring is more suitable
(Kirkwood & Sterne, 2003).
Initial review showed no specific trends across all the 34 measures; however, there
was a predominance of lognormal distributions so the variables were transformed
75
using a logarithmic approach then re-assessed via the Anderson-Darling test. There
was an improvement in the result, with approximately 30% of the logarithmically
transformed variables found to be normally distributed.
At this stage, there was some consideration given to the possibility that the
Anderson-Darling test may have been overly conservative, as it was detecting
relatively small departures from normality. Ultimately, the decision as to whether the
descriptive statistics on this occasion should be approached via means as averages or
a median average does not require perfect normality, and hence an alternative
approach was adopted. A set of criteria (Appendix 5) to determine normality more
appropriate to the investigation was applied to both the crude data and the
transformed data. Data were required to meet each of the six criteria to be classified
as normally distributed.
The majority of the data could not be normalised and, whilst it would be possible to
split the data interrogation into parametric and non-parametric analyses, the benefit
of being able to utilise the more powerful parametric methods would come at a cost
of introducing significantly more complexity to the analysis than was warranted. As
such, non-parametric methods were selected for analysis of the data, describing and
comparing median averages rather than means. This involved the use of the MannWhitney and Kruskal-Wallis sample tests for the two- and three-population median
comparisons, respectively, in hypotheses 1 and 2. For hypothesis 3, multiple linear
regressions were utilised to determine the predictability of the personal air
monitoring for the 1-OHP in urine. Dichotomous variables (forming = 1, nonforming = 0) (no PPE = 1, PPE = 0) and (smoking = 1, non-smoking = 0) were also
used in the regression analyses.
As there were both continuous and categorical data to be analysed, linear regression
was well suited to predict the outcome on the basis of the available independent
variables, which was further simplified by eliminating some of the predictors. From
here the simplified equation for the prediction of 1-hydroxypyrene from initially
BSF and potentially other elements (i.e. smoking, PPE) was assessed for its
predictive power. Regression is best when observations are independent of each
other and this assumption was met by reviewing the data set, and where identified,
76
removing results that were repeated from the same individuals as is discussed in
section 4.4.1.1.
Extreme cases have too much impact on the regression solution and also affect the
precision of estimation of the regression coefficient estimates (Tabachnick, Fidell
2007). Hence the data were reviewed to ascertain the possible presence of outliers.
Outliers were identified (see section 3.6.1) and consequently not included in the
analyses. As the presence of multicollinearity can affect the estimation of the
regression coefficients, correlations between the independent variables were tested
and found to be low, hence indicating an absence of multicollinearity. Finally, the
normality of residuals was also tested for the models and displayed some differences
between the groups. The anode plant forming and non-forming groups exhibited
some minor curvature in the tail of the normal probability plot which indicated some
skewness of the data. The data from reconstruction had a higher level of skewness
due to the increased number of results in the lower values. These deviations from the
model could also have resulted from the non-normality of the data.
The standardised normal probability plot for the all-data model did not fit the line but
displayed some curvature. This is not unexpected given that it included data from
reconstruction which would have a significant impact. Additionally there is the
possibility that this could indicate a missing variable from the model and also an
issue with the homogeneity of the variances, particularly between the reconstruction
and anode plant areas (as highlighted in section 4.2.3).
3.6.1 Outliers
Whilst data were spread over a wide range of values, there were two urine sample
results with significantly larger 1-OHP concentrations than any other measures
obtained: one from a former technician (112.85 µmol/mol cr) and another from a
mechanical maintenance technician (85.14 µmol/mol cr). Both were working in the
forming area of the anode plant at the time. All other urine sample values were
below 50.0 µmol/mol cr. Further investigation of the samples, which involved
discussions with the individuals concerned and review of work logs, revealed that on
both occasions there were significant plant disruptions that required manual
intervention on the part of the operator. In both cases a paste ‘dig out’ was required.
77
In this scenario, the operator must enter the area where the blockage has occurred
and physically shovel out the coal-tar paste before it cools and sets. This results in
much higher levels of skin contact with the coal-tar pitch along with longer intervals
between washing of the skin due to the nature of the task. This is not a common
occurrence, but there have been a few such instances in the past. Whether these
results should be included as part of the routine operating of a carbon anode plant is
dependent on the view taken. If a plant is operating to specification, i.e. within
operating parameters and in control, then this is an uncommon situation. However,
where a plant is being operated at or beyond its design capacity or the preventative
maintenance program is not in control, these situations become more common,
making them a part of the routine tasks and a serious concern. The impact of these
outliers will be assessed in section 4.4.1.2, and discussed in relation to the issue of
poor maintenance and failing equipment in section 5.1.3.
78
4.0 RESULTS
This chapter presents the results for air and biological monitoring in various areas of
the prebake smelter. Statistical relationships are examined, and the results from
comparison of the data sets in relation to the three hypotheses are presented. Also
included are results from data collected before and after the plant process
intervention.
4.1
Introduction
A total of 166 sets of pre- and post-shift urine samples were collected from the
cohort for analysis of 1-OHP. Of these, 20 were not within the creatinine range
specified by the method’s guideline and 18 were missing the post-shift sample, and
were therefore excluded from the analysis. From the control group, 24 sets of
samples were collected. In addition, 167 personal air samples and 249 static air
samples were collected and analysed for BSF, and there were 58 matched sets of 1OHP urine results with a corresponding personal BSF in air result.
As detailed in section 3.6, non-parametric analyses were selected as the approach for
the data interrogation to test the hypotheses:
In a prebake smelter, based on the results of static air monitoring of the process,
personal air monitoring of the individual and biological monitoring:
1. Workers in the carbon anode plant will have higher exposure to PAHs than
workers in the cell-reconstruction area of the smelter.
2. Within the carbon anode plant, exposure to PAHs will be higher among
workers involved in tasks associated with the paste-mixing and anodeforming areas than those in the non-forming areas of the carbon anode
plant.
3. There is no evidence of a relationship between personal air monitoring for
the BSF and 1-OHP in urine of workers involved with tasks in a prebake
smelter.
79
To test hypotheses 1 and 2, the two-sample Mann-Whitney test (equivalent to the
two-sample rank or two-sample Wilcoxon rank sum tests) was used to make
inferences about the difference between two population medians, based on data from
two independent, random samples. A significance level of α = 0.05 (two-tailed) was
used in these assessments. The Mann-Whitney test was the non-parametric test of
choice for comparing the groups where the tests only involved comparison of two
groups at a time, i.e. anode plant and cell-reconstruction group, or anode forming
area and anode non-forming area.
Where three populations were assessed (i.e. reconstruction, anode plant forming and
anode plant non-forming areas for hypothesis 2), the Kruskal-Wallis test for one-way
analysis of variance was utilised, as it is an extension of the Mann-Whitney test for
three or more independent groups. This assessment primarily looked at the exposure
of two anode-plant areas (forming and non-forming), including a comparison with
the reconstruction area. Whilst not strictly addressing hypothesis 2, it was considered
valuable as an overall gauge of exposure across the sites for later discussion.
Hypothesis 1 was considered in terms of three groups of different sample
measurements:
•
BSF in air static samples for anode plant and the cell-reconstruction area;
personal BSF in air samples for operators in the anode plant and cellreconstruction area; and
•
1-OHP samples in urine of the operators for the anode plant and cellreconstruction areas.
•
A similar comparison process was utilised to assess the 1-OHP levels in urine
of the different groups for hypothesis 2.
For hypothesis 3, BSF and 1-OHP results were assessed via bivariate correlations in
the first instance and multivariable linear regression analysis in the second, which
considered potential confounders of smoking and PPE.
Measurements of the
confounders were addressed in the pre-sampling questionnaire.
80
4.2
Exposure variation in a prebake smelter (hypothesis 1)
Workers in the carbon anode plant will have higher exposure to PAHs than workers
in the cell-reconstruction area of the smelter
Table 4.1 presents average (median) exposure levels from both static and personal
BSF monitoring and 1-OHP levels in urine as discussed in the sections below. All 1OHP levels in urine for the control group were below the level of detection.
Table 4.1: Median static and personal measures of BSF in air and 1-OHP in urine, by
sections within a prebake smelter
Reconstruction
Static BSF exposure
No. samples
Median (range, mg/m3)
Personal BSF exposure
No. samples
Median (range, mg/m3)
1-OHP
No. samples
Median (range, µmol/mol cr)
Anode Plant
Anode plant total
Forming
Non-forming
66
0.013 (0.003-0.154)
183
0.023 (0.002-0.250)
66
0.030 (0.002-0.250)
117
0.019 (0.003-0.197)
27
0.054 (0.003-0.371)
140
0.036 (0.003-0.563)
71
0.046 (0.003-0.563)
69
0.028 (0.003-0.128)
25
0.17 (0.001-2.47)
94
6.62 (0.090-33.44)
44
14.20 (2.02-33.44)
50
4.11 (0.09-26.99)
4.2.1 Static exposure levels
The median static BSF in air in the anode plant was 0.023 mg/m3, almost twice as
high as that in the cell-reconstruction area (median 0.013 mg/m3). This difference
was statistically significant (p = 0.030). The range of variation of the static BSF in
air within the anode plant was also greater than that of the reconstruction area,
indicating that there were a variety of point sources within the anode plant with
higher fugitive emissions.
4.2.2 Personal exposure levels
Median BSF exposure level in the anode plant was 0.036 mg/m3, significantly lower
(p = 0.041) than the median exposure level in the reconstruction area, which was
81
0.054 mg/m3. Variation in the personal air monitoring of BSF was higher in the
anode plant than in the reconstruction area.
4.2.3 Biological 1-OHP levels
Comparison of the median 1-OHP levels from the anode-plant workers and the
reconstruction-area workers showed that 1-OHP concentrations were significantly
higher in the anode-plant workers (p < 0.001); 6.62 compared with 0.17 µmol/mol
cr, respectively. A comparison of the variances within the reconstruction area and the
anode plant identified the difference in variation to be substantial. Transformation of
the data using squared, log and natural logarithm functions produced marginal
improvement, but insufficient to demonstrate a homogeneity of the variances
between the reconstruction and anode plant areas. Therefore, it should be noted that
in the comparisons undertaken in the first hypothesis this anomaly exists.
Based on static monitoring of air levels for BSF and of 1-OHP levels in urine, the
anode plant had the higher exposure. However, the personal BSF air monitoring
indicates that the monitored section of the cell-reconstruction area of the plant had a
higher level of airborne PAHs reaching the workers.
These results suggest that workers in the reconstruction area were exposed to higher
levels of airborne PAHs than workers in the carbon anode plant, but that anode-plant
workers potentially had higher exposure via other routes than air. This may be due to
processes involved, one being a more controlled construction of a cell compared
with a production role that can require a higher level of process intervention due to
failures or breakdowns in the anode plant. This can result in increased skin contact
and additional exposure. Another consideration is that the reconstruction workers
were positioned within a smaller physical location and their work took place mainly
within the confines of the reduction cell being constructed. Although the actual
levels may be lower, these workers are spending more time in areas where there are
fugitive emissions. The anode-plant workers operated across a much larger plant
area, with a greater variation of sources and exposure levels and this is reflected in
the range of measured values.
82
Static BSF Monitoring
0.25
BSF (mg/m3)
0.20
0.15
0.10
0.05
0.00
Anode Plant
Anode Plant Forming
Anode Plant non-Forming
Reconstruction
Figure 4.1: Static air BSF measures in the anode plant, anode plant forming area,
anode plant non-forming area and reconstruction area in a prebake smelter in
Queensland, Australia, 2002–04
Personal BSF Monitoring
0.6
0.5
BSF (mg/m3)
0.4
0.3
0.2
0.1
0.0
A node Plant
A node Plant Forming
A node Plant non-Forming
Reconstruction
Figure 4.2: Personal air BSF measures of workers in the anode plant, anode plant
forming area, anode plant non-forming area and reconstruction area in a prebake
smelter in Queensland, Australia, 2002-04
83
1-Hydroxypyrene in Urine
35
1-OHP (umol/mol cr)
30
25
20
15
10
5
0
Anode Plant
Anode Plant Forming
Anode Plant non-Forming
Reconstruction
Figure 4.3: 1-OHP in urine of workers in the anode plant, anode plant forming area,
anode plant non-forming area and reconstruction area in a prebake smelter in
Queensland, Australia, 2002-04
4.3
Exposure variation in an anode plant of a prebake
smelter (hypothesis 2)
Within the carbon anode plant, exposure to PAHs will be higher among workers
involved in tasks associated with the paste-mixing and anode-forming areas than
those in the non-forming areas of the carbon anode plant.
4.3.1 Static exposure levels
Median static BSF in air in the forming area of the anode plant was 0.030 mg/m3
compared to 0.019 mg/m3 in the anode plant non-forming area. This difference was
statistically different (p = 0.041).
84
4.3.2 Personal exposure levels
A Kruskal-Wallis test comparing the reconstruction group, anode forming group and
anode non-forming group detected significant differences in personal BSF exposure
levels across areas of the prebake smelter (p < 0.001). Post hoc Mann-Whitney
pairwise comparisons identified statistically significant differences in personal BSF
levels between the forming and non-forming sections of the anode plant (p < 0.001),
with more individual variation in measurements in the forming compared to nonforming area and a higher median of 0.046 mg/m3 compared to a median of 0.028
mg/m3, respectively. Comparing each of these anode plant areas to the reconstruction
area, which had a median personal BSF exposure of 0.054 mg/m3, exposure was
statistically similar in the forming area of the anode plant (p = 0.880), but
approximately half that of the non-forming area (p = 0.0002).
4.3.3 Biological 1-OHP levels
The 1-OHP results present a greater difference between the two plant areas within
the anode plant than the differences between BSF-monitored PAH concentrations.
The median result from the forming area of the anode plant (14.20 µmol/mol cr) is
more than three times higher than that from the non-forming area (4.11 µmol/mol cr,
p < 0.001). Both are significantly higher than the measures obtained from the
reconstruction area (0.17 µmol/mol cr).
Based on the results presented in Table 4.1, it follows that within the carbon anode
plant, exposure to PAHs appears highest among workers involved in tasks associated
with the anode-forming areas.
4.4
Personal air monitoring of BSF exposure and
relationship to 1-OHP levels in urine (hypothesis 3)
There is no evidence of a relationship between personal air monitoring for the BSF
and 1-OHP in urine of workers involved with tasks in a prebake smelter.
85
4.4.1 Preliminary analysis ignoring potential confounders
On 58 occasions, personal BSF air monitoring was undertaken to correspond to a 1OHP monitoring run on the participants in the anode plant forming area, anode plant
non-forming area and the reconstruction area. This information was analysed by
regression analysis to determine the predictive value of BSF in air personal
monitoring in relation to the 1-OHP in urine samples post-shift (collected at the end
of the last shift rotation) minus pre-shift (collected at the beginning of the first shift
of the rotation).
4.4.1.1 Sensitivity of conclusion to presence of multiple measures
Within this group of samples were six participants who were sampled twice or more.
This is inevitable in a sampling program where there are limited numbers of
employees and low staff turnover during the sampling period. There were two
participants in the anode plant forming area who provided samples on two and three
occasions. Also, one participant in each of the anode plant non-forming and
reconstruction areas provided samples on two occasions. Hence, five out of 66
samples were not strictly independent observations. To determine the potential
impact of recurrent individuals in the sample (since their inclusion violates the
assumption of independence of samples required for valid application of the
statistical tests), only their first-occurrence sample results were included.
4.4.1.2 Impact of outlier
Within the data was one pair of results from the anode plant forming area that was
substantially higher than any of the others. This sample was previously discussed in
section 3.6.1. This participant’s 1-OHP value for post-shift minus pre-shift was
111.38 µmol/mol cr, more than three times the next highest sample value. The
corresponding personal BSF result was 0.44 mg/m3, also significantly higher than
the other BSF results. Investigation of the cause of these differences revealed that
86
there were significant plant problems during the shift and manual intervention was
required to dig out the pitch from the equipment before it set hard. Because this is
not a common occurrence, the outlier was not included in the final analyses. When
the outlier was removed from the combined analysis, anode plant analysis and the
anode plant forming analysis, there was a significant impact on the R2 (adj) result for
the three regression analyses. The result for all the plant reduced from 38.7 – 0.7%,
the anode plant from 39.9 – 0.4% and the anode plant forming from 35.6 – 0.0%.
This presented a very different picture and showed that BSF in air is a poor predictor
of 1-OHP in urine across the prebake smelter.
4.4.2 Multiple linear regressions
The bivariate analyses above may be biased by potential confounding influences of
smoking, diet, use of PPE, and contact with other coal-tar products outside of the
occupational environment. These may distort the magnitude of the noted associations
between smelter area and exposure to PAHs as measured by 1-OHP, by varying
degrees as discussed in section 2.4. The multiple linear regression analyses
considered the potential for confounding of these variables by extending the original
bivariate associations to adjust for all identified confounders.
Adjusted and
unadjusted results were compared and any regression coefficients that differed by
more than 10% are reported in terms of adjusted results, as these are closer to a
truthful association than the bivariate results.
4.4.2.1 Role of confounders
As part of the monitoring program for 1-OHP, participants were asked to complete a
questionnaire prior to the collection of the sample as described in section 3.5.2.3.
Statistically, a variable is identified as a potential confounder if it is associated with
both the outcome of interest, in this case 1-OHP levels, and the independent variable
(in this case BSF for hypothesis 3) in the main bivariate analysis. Associations
between potential confounders and outcome are presented in Table 4.2. These
associations were evaluated for statistical significance using the Mann-Whitney test
in relation to possible impacts on the 1-OHP levels.
87
The comparison for smoking and non-smoking groups showed a statistically
significant difference at both the pre- and post-shift timepoints, with the median of
the pre-shift values among smokers at 0.82 µmol/mol cr (p = 0.009), which is higher
than that of the non-smokers (0.31 µmol/mol cr). The comparison of the post-shift
results showed that the smokers’ median was 10.75 µmol/mol cr, which was a higher
value than the non-smokers’ at 4.97 µmol/mol cr (p = 0.011).
Table 4.2: Identification of potential confounding variables of the association between
1-OHP levels and personal BSF levels
n
Median 1-OHP
(µmol/mol cr)
30
0.82
0.21 – 9.59
No 123
0.31
0.21 – 13.6
Yes
26
10.75
0.21 – 112.85 0.011
No 109
4.97
0.21 – 31.79
Yes
31
0.77
0.21 – 28.09
No 254
0.83
0.21 – 112.85
Use of coal-tar products Yes 15
(pre-shift)
No 137
0.51
0.21 – 0.85
0.32
0.13 – 13.60
Yes 227
0.93
0.21 – 85.14
No
13
2.7
0.21 – 112.85
Yes
11
7.39
1.28 - 19.46
No
21
8.45
3.69 – 46.0
Potential confounder
Smoking (pre-shift)
Smoking (post-shift)
PAH exposure at home
PPE used
Yes
Range
p-value
(µmol/mol cr)
0.009
0.89
0.91
0.27
Overalls used in forming
area
0.10
For non-occupational exposure to PAH from sources such as food, wood
preservatives and personal care coal-tar products (e.g. soaps, shampoo), there was no
significant difference between the use and non-use groups. Further investigation of
pre- and post-shift response for the use of coal-tar products also did not yield a
significant difference between urine measures.
The median value of 1-OHP among those who did not use PPE was approximately
three times that for those who did report using PPE (2.70 µmol/mol cr compared to
88
0.93 µmol/mol cr); however, the difference did not reach statistical significance (p =
0.27). The different mandatory base levels of PPE required depending on the area
and task (as discussed in section 3.5.2.3) could have impacted on this result; it is also
possible that the selected PPE may not have been effective. The use of overalls by a
specific group of employees in the forming area was also assessed to determine if
there was a significant impact. The median values between those who wore the
overalls and those who did not showed only a small difference (7.35 vs 8.45
respectively); however there was a much larger variation in the range, and whilst the
difference was not statistically significant (p = 0.10), it was believed it merited
further assessment.
Of the potential confounders reviewed in Table 4.2, the use of coal-tar products at
home and the consumption of foods that may potentially contain PAHs (e.g. smoked
products or barbecued foods) appeared to have little impact and therefore were not
considered further in the multivariate analyses. In contrast, these analyses identified
different levels of potential impact for smoking and use of PPE; therefore, these
warranted further investigation.
4.4.2.2 Adjustment for identified confounders
The possible impact of smoking and PPE on the results required further analysis to
determine whether smoking or not wearing PPE served as confounders or displayed
effect modification of the relationship between BSF and the level of 1-OHP in urine.
Multivariate regression analyses were undertaken on the data, which were presented
in four models:
1. All groups combined (Table 4.3)
2. Anode plant (Table 4.4)
3. Anode plant forming area (Table 4.5)
4. Anode plant non-forming area (Table 4.6)
Each model was assessed by comparing the 1-OHP concentration in urine against:
•
BSF in air personal monitoring;
•
smoking;
•
PPE; and
89
•
BSF, smoking and PPE.
The analyses of the impact of smoking and PPE were not undertaken for the
reconstruction area as all participants in this group were non-smokers and wore PPE
at all times. However, data from reconstruction area workers were included in the
‘All groups combined’ analyses.
Table 4.3: Relationship of 1-OHP levels and BSF for all samples in the anode plant
and reconstruction areas at a prebake smelter site: impact of identified confounding
variables (n = 58)
Variables in
model
Bivariate
regression
coefficients
(SE)
p-value
Adjustedb
regression
coefficients
(SE)
p-value
BSF
(mg/m3)
24.0 (20.3)
0.24
24.3 (21.0)
0.25
0.71
0a
1.1 (3.0)
0.71
0.82
0a
-0.19 (2.4)
0.94
Smoking
PPE
adj R2 (%)
a
b
No
Yes
0a
1.1 (2.9)
Yes
No
0a
0.5 (2.3)
0.7
0
referent category
adjusted for all other variables in the table
There appears to be no confounding of the bivariate relationship between 1-OHP
levels and BSF across all samples taken. For every 1 mg/m3 increase in BSF there
was a 24.3 µmol/mol cr increase of 1-OHP in the adjusted model compared with the
unadjusted value of 24.0 µmol/mol cr. Smoking and PPE did not display significant
relationships with 1-OHP in this model. The predictive ability of the model to
estimate 1-OHP levels was minimal, with the adjusted R2 < 1.0.
A similar approach as that taken for the combined group model was then utilised to
assess the samples from workers in the anode plant only. These are summarised in
Table 4.4.
90
Table 4.4: Relationship of 1-OHP levels and BSF in the anode plant at the prebake
smelter site: impact of identified confounding variables (n = 39)
Variables in
model
Bivariate
regression
coefficients
(SE)
p-value
Adjustedb
regression
coefficients
(SE)
p-value
BSF
(mg/m3)
26.1 (23.9)
0.28
33.5 (24.0)
0.17
0.47
0a
-1.5 (3.1)
0.63
0.17
0a
-4.3 (2.7)
0.13
Smoking
PPE
No
Yes
0a
-2.3 (3.2)
Yes
No
0a
-3.7 (2.6)
adj R2 (%)
a
b
0.4
0
referent category
adjusted for all other variables in the table
There appears to be some confounding of the bivariate relationship between 1-OHP
levels and BSF across the anode plant. On average, for each 1 mg/m3 increase in
BSF, 1-OHP levels increased by 33.5 µmol/mol cr, after adjustment for smoking and
the use of PPE. This was different from the unadjusted estimate of 26.1 µmol/mol cr.
This variation was deemed to warrant further investigation. The predictive ability of
this model to estimate 1-OHP levels was still minimal, as evidenced by the adjusted
R2 of 0.4 and 0.
The anode plant warranted further investigation in terms of the forming and nonforming areas. These are summarised in Tables 4.5 and 4.6
91
Table 4.5: Relationship of 1-OHP levels and BSF in the anode plant forming area at the
prebake smelter site: impact of identified confounding variables (n = 17)
Variables
in model
Bivariate
regression
coefficients
(SE)
p-value
Adjustedb
regression
coefficients
(SE)
p-value
BSF
(mg/m3)
3.6 (30.7)
0.92
-0.4 (37.6)
0.99
0.37
0a
3.6 (7.1)
0.62
No
Yes
0a
3.9 (5.2)
PPE
Yes
No
2.9 (4.2)
0a
Overalls
Yes
No
Smoking
adj R2 (%)
a
b
1.7 (5.4)
0a
0.76
-0.81 (6.2)
0a
-1.9 (7.9)
0a
0.82
0
0
0.50
referent category
adjusted for all other variables in the table
As part of the questionnaire individuals were also asked to specify what PPE they
were wearing. This information was able to be used to determine whether individuals
were wearing overalls during the performance of their work or only other PPE.
These impermeable overalls are intended to provide additional protection from skin
contamination and their use was included as an additional variable in the regression
analysis of the anode plant forming area as this is an area where skin contact is a
particular issue.
On reviewing the results for the anode plant forming area, there was a small
difference between the unadjusted and adjusted results for BSF. An increase of 1
mg/m3 of BSF resulted in an increase of 3.6 µmol/mol cr in the unadjusted model but
resulted in a minor decrease in the adjusted model, a difference of only 4.0 µmol/mol
cr. The use of overalls appeared to result in a small negative result which decreased
from -0.81 to -1.9 µmol/mol cr. The predictive ability was non-existent with the
adjusted R2 = 0.0 in both cases.
In the case of the anode plant non-forming model (Table 4.6), there appeared to be a
difference indicating a potential confounding of the bivariate relationship, with the
92
unadjusted model coefficient at –27.7 and the adjusted model coefficient at –31.3.
However, considering the impact of smoking and PPE on the association with BSF
separately, there appeared to be a lowering of the 1-OHP in the urine of smokers and
those wearing PPE. It would be expected that the levels would reduce if PPE is worn
as it protects the individual from exposure, but it appears counter intuitive in the
lowering of 1-OHP among smokers. Evaluation of the group via a cross tabulation of
the smoking and PPE, showed that 40% of the smokers also wore PPE. There was
also an increase in the predictive ability of the unadjusted model increasing from 0%
for the bivariate association to 11.4% for the adjusted.
Table 4.6: Relationship of 1-OHP levels and BSF in the anode plant non-forming area
at the prebake smelter site: impact of identified confounding variables (n = 22)
Variables
in model
Bivariate
regression
coefficients
(SE)
p-value
Adjustedb
regression
coefficients
(SE)
p-value
BSF
(mg/m3)
-27.7 (37.4)
0.45
-31.3 (40.6)
0.45
0.06
0a
-4.9 (3.4)
0. 17
0.07
0a
-1.71 (3.1)
0.59
Smoking
PPE
adj R2 (%)
a
b
No
Yes
0a
-5.4 (2.7)
Yes
No
0a
-4.48 (2.4)
0.00
11.4
referent category
adjusted for all other variables in the table
4.4.2.3 Skin Exposure.
On the questionnaire, were three questions relating to perceived skin contamination.
Employees were asked to select one which they believed was the closest
representation of their exposure during the shifts. These were:
•
Level 1: Minimal to no opportunity noted for visible contamination of skin
or clothing with CTP, or carbon material known to contain CTP.
•
Level 2: Periodic opportunities for visible contamination of skin or clothing.
•
Level 3: Regular or routine visible contamination of skin or clothing
93
This information was then assessed via linear regression with results presented in
table 4.7. The perceived skin exposure appears to have some relationship with the
increase of 1-hydroxypyrene in urine. There is an increase of 7.4 µmol/mol cr
associated with the skin exposure as rated by the employees. The PPE has a much
smaller impact (1.7 µmol/mol cr) which includes a reduction in the adjusted R2 value
from 11.5% to 10.2 %
Table 4.7: Relationship of 1-OHP levels and skin exposure in the anode plant and
reconstruction area at the prebake smelter site: impact of identified confounding
variables (n = 66)
Variables
in model
Bivariate
regression
coefficients
(SE)
Skin
Exposure
1
2or 3
0a
7.4 (2.4)
PPE
Yes
No
1.7 (4.0)
0a
adj R2 (%)
11.5
p-value
Adjustedb
regression
coefficients
(SE)
p-value
0.003
7.3 (2.4)
0.003
0.67
1.2 (3.7)
0a
0.75
10.2
4.4.2.4 Potential effect modification (subgroup differences in size of
association)
As established in studies by Ferreira et al. (1994) and Angerer et al. (1997) in
graphite electrode plants, by van Rooij et al. (1992) in an aluminium smelter and by
van Rooij et al. (1993a, 1994a) in a coke oven, there is reason to further test the
relationship between work-area PAH exposure effects, BSF and 1-OHP. This effect
was considered by extending the model in Table 4.4 with a term reflecting the
interaction of the work area variable (Table 4.7).
As hypothesised, work area location was a significant modifier of the relationship
between 1-OHP levels and BSF. On average, those who worked in the anode plant
had increased levels of 1-OHP, 26.14 (SE± 23.86) µmol/mol cr for every 1 mg/m3 of
BSF. Compared to this overall group, those who worked in the forming area had
substantially higher levels of 70.1 (SE± 16.98) µmol/mol cr on average.
94
Table 4.8: Degree of effect modification, by work area, of the relationship between
1-OHP levels and BSF among workers in all the combined groups
Variables in model
Adjustedb
regression
coefficient
(SE)
p-value
BSF (mg/m3)
26.1 (23.9)
0.25
No
Yes
0a
10.8 (1.67)
<0.001
No
Yes
0a
70.1 (16.98)
<0.001
Work area (Forming)
BSF x work area (Forming)
adj R2(%)
a
b
22
referent category
adjusted for all other variables in the table
4.5
Process intervention results
During preliminary data analysis, it was identified that there were potential areas of
improvement available to enable a reduction in exposure for some of the SEGs.
Whilst not part of the original research project, this provided an opportunity to
further assess the exposure of the workers. After consultation with site and area
management teams, it was decided that, rather than wait until extensive data analysis
was completed, the improvement opportunities should be implemented and trialled
as soon as possible. Six months after the implementation of these changes, a small
monitoring program was undertaken and continued each six months from then on to
track whether the changes had any impact on measured exposure level. Results for
the green carbon maintenance team from early 2005 through to June 2006 are
presented in Table 4.8. It was not possible to directly compare all the results during
this period as the SEGs had changed significantly as part of the improvement plan.
However, by selecting an unaltered work group of maintenance employees, it was
possible to compare the results before and after the changes.
95
Table 4.9: 1-OHP in urine post-shift minus pre-shift for green carbon maintenance
SEG sampled before and after changes implemented in 2005
1-OHP levels
Green carbon
maintenance staff
pre-January 2005
Green carbon
maintenance staff
post-January 2005
No. participants
32
32
Median (range, µmol/mol cr)
5.49 (0.39-27.0)
2.36 (0.00-8.53)
Comparison of the 1-OHP levels from the green carbon maintenance workers preJanuary 2005 with post-January 2005 results showed substantial decreases in both
median values and the range of measurements. The upper end of the range decreased
by a factor of three, and the median was substantially higher prior to the
modifications than after the modifications (5.49 µmol/mol cr compared with 2.36
µmol/mol cr, respectively; p < 0.001).
96
5.0 DISCUSSION
This chapter discusses the research findings and examines the results in relation to
other relevant studies. The study’s strengths and limitations are considered, and
recommendations are made for future research and implementation of control
measures.
5.1
Introduction
This study identified two areas within a prebake smelter in which there was an
identified exposure to PAHs; both areas involved tasks associated with the
construction of an aluminium reduction cell. Initially, static and personal air samples,
the traditional measures of exposure, were analysed and compared. A total of 249
static BSF air samples, 167 personal BSF air samples and 119 1-OHP in urine
samples were available for assessment of the anode plant and cell-reconstruction
areas. Included in these were 58 personal BSF air samples with a corresponding 1OHP urine sample. Biological monitoring of 1-OHP was reviewed to determine if
there was an alignment of the predicted exposures across and within SEGs.
Levels of PAH in air at static sampling locations, air in the participants’ personal
breathing zone and the level of 1-OHP in urine of these participants were
determined. Assessing BSF in air and 1-OHP in urine provided information covering
the inhalation route of exposure and also any potential exposures arising from
ingestion or skin contact. The latter was particularly important, as the dermal route
has been identified as a possible source of exposure.
The third assessment was based around the 58 personal samples for BSF and 58 sets
of urine samples for 1-OHP collected during the same work period. This was utilised
to investigate the predictive ability of the personal BSF of airborne samples in
relation to the level of 1-OHP in urine of the workers in the plant. This would also
help address study objectives relating to the assessment of the potential impact of
97
skin contact to compounds containing PAHs, and evaluation of the utility of
monitoring 1-OHP in urine of workers as a routine method for determining exposure
to PAHs in an anode-manufacturing facility in a modern prebake aluminium smelter.
Should this be viable, then a review of the applicability of a biological exposure
index guideline for 1-OHP in urine for aluminium smelting at an Australian smelter
is warranted.
5.1.1 Exposures compared between the anode plant and the cellreconstruction area of a prebake smelter
The median static BSF in air in the anode plant was 0.023 mg/m3 (range 0.002–
0.250), almost twice as high as that in the cell-reconstruction area (median 0.013
mg/m3, range 0.003–0.154). The median BSF personal exposure level in the anode
plant was 0.036 mg/m3 (range 0.003–0.563), significantly lower (p = 0.041) than the
median exposure level in the reconstruction area which was 0.054 mg/m3 (range
0.003–0.371). Both these results were below the recommended occupational
exposure limit of 0.1 mg/m3 based on a 12-hour shift rotation.
There is an inconsistency in relation to the static BSF samples and the personal BSF
samples in the reconstruction area; the low level of BSF in air in the static samples
does not correspond to the relatively high levels in the personal BSF in air samples.
There are, however, different scenarios that can result in such an outcome. Firstly,
this is an important example of the difference between static air monitoring and
personal air monitoring which underpins the rationale for not using static air
monitoring to assess personal exposure of a worker. Static monitoring gives an
indication of the airborne levels of contaminant in a particular location of the plant
and hence is a useful tool for identifying where fugitive emissions may be occurring
and if controls are either not present or ineffective. This does not mean that a worker
will necessarily be exposed at that level. The results are based on a TWA. As such, a
worker who is usually very mobile, due to the nature of his/her tasks, will move
through different areas of the plant and may only spend a short period of time in an
area of high emission or, alternatively, may spend a longer period of time in an area
of lower emissions. In the case of the reconstruction area, the static BSF levels may
98
be lower than the anode-plant sources, but the reconstruction-area worker will spend
the majority of his/her shift in the cell where rebuilding is taking place, which is the
main environment of his/her potential exposure. The anode-plant worker is more
mobile and may be required to move through many areas during the day, varying
from low to high potential exposures, and thus experience an overall average lower
exposure to the airborne contaminants, despite the fact that the sources with the
highest absolute air levels occur in this work location.
Secondly, the results can reflect incorrect selection of the location of the static
samples. When the static sample locations are not in the vicinity of the main sources
of the exposure, the results produced may be artificially low. The location of the
static reconstruction area samples were widely dispersed, including the work areas
and walkways inside and around the cell. These were further from the emission
sources, but were regarded as part of the main work area of the reconstruction crews.
Some of the resulting exposure would have been minimised by the sampling
protocol, but this cannot be completely ruled out as the tasks undertaken will vary
the movement of the individual. To ensure all variations are accounted for would
require larger sample numbers to cover more locations for a greater number of days.
Thirdly, and discussed in more detail in section 5.1.4, is the wearing of PPE,
particularly respirators, in areas where the primary route of exposure is inhalation of
fume or particulate in the air. Levels can be quite high in the air, but wearing an
appropriately fitted and maintained respirator has the capacity to minimise the
amount of contaminant getting into the body. To gain a clearer picture of personal
exposure, it is appropriate to refer to the biological monitoring results for the
different work locations.
The median of the 1-OHP measures showed that levels were significantly higher
from the anode plant than the reconstruction area: 6.62 µmol/mol cr (range 0.09–
33.44) compared with 0.17 µmol/mol cr (range 0.001–2.47), respectively (p <
0.001). This is more than an order of magnitude different, with a much wider range,
and aligns with the static monitoring results. As the biological samples provide an
indication of the total body burden, they may indicate that whilst the personal air
samples from the reconstruction area were higher than from the anode plant, the
99
actual dose being absorbed by the worker is much lower for the reconstruction area
compared with the anode plant, which is counter intuitive. Three possible reasons for
this are:
1. The exposure in the reconstruction area is predominantly airborne and the
respiratory protection is effective in reducing the actual dose being absorbed
into the body.
Observation of the tasks undertaken in the reconstruction area indicated that the
majority of exposure comes from fumes emitted from the ramming paste and from
the liquid pitch that is painted onto the walls of the cell to increase the adhesion of
the paste during the ramming process. Respiratory protection is mandated when
working in the cell, with air-fed respirators and disposable coveralls required
whenever working with liquid pitch. Those not working directly with liquid pitch
application use negative-pressure silicone half-face cartridge respirators. As
explained in section 3.3.6, all workers are ‘quantitatively’ face-fitted for their
respirator and trained in the use and maintenance of the equipment. There is limited
opportunity for ramming paste or liquid pitch to come in contact with skin, but a
strong organic bitumous odour pervades the air in the vicinity of the cells when
ramming is undertaken. Although it is possible that fume could be absorbed onto the
skin along with some of the particulate matter originating from airborne dried paste
residue, this is inconsistent with the low results of the 1-OHP measures and would
indicate that it is not a major contributor to the total dose in the reconstruction area.
Incidentally, operators have commented that the odour is a very useful early warning
sign if the face seal on the respirator is broken or the filters are losing effectiveness
and require replacement. It appears that the volatile fumes of the pitch and
particulate are the main source of exposure for reconstruction-area workers. Whilst
personal air samples may be elevated, the body burden is quite low, indicating that
the respiratory protection is effective and there is minimal exposure via ingestion or
skin contact. This aligns with the static and personal BSF results obtained.
2. The higher body dose in workers from the anode plant is due to failure or
inefficiency of their respiratory protection.
100
In the anode plant there are numerous and varied types of air exposures, ranging
from high fume exposure when maintaining some pieces of equipment, such as the
vibration plate in green carbon and in the vicinity of the vibro-former, to the lower
fume levels associated with the anode bake furnaces. Also, there is potential for
contact with the pitch paste when cleaning pieces of equipment prior to release for
maintenance or as a result of a process intervention or general maintenance on the
plant and equipment. The respiratory PPE requirements within the anode plant are
similar, but not identical, to those in the reconstruction area and follow the same
testing, training and maintenance program. The PPE requirements can vary
according to task, and the requirement for respiratory protection is not mandated
across all parts of the plant allowing some worker discretion. For example, while all
areas of the green carbon plant require respiratory protection, only when in the
immediate vicinity of the bake furnace is use of a respirator mandatory. Half-face,
silicon negative-pressure cartridge respirators are the main units in use with full-face
negative-pressure respirators used for some specific tasks. Compliance with
respirator-wearing requirements is very good and is regularly monitored by the
manager and peer interactions. There appears to be no reason why the efficiency of
the respirators in the anode plant should be any lower than in the reconstruction area
given the care and attention administered to this control. Consequently, this would
exclude the likelihood that the higher body dose in the anode plant has resulted from
failure or inefficiency of respiratory protection.
3. There is another route of entry for which an effective control has not been put
in place, i.e. ingestion or skin contamination of materials containing PAHs.
If fume levels are relatively low, but there exists the opportunity for skin contact or
ingestion, it is possible to exhibit high levels of 1-OHP in urine. This route of
exposure cannot be measured via the traditional BSF air monitoring program. Hence,
it would be possible to detect low levels in air monitoring when, in fact, there is a
higher body burden as a result of exposure via the skin and/or ingestion. As
discussed in section 2.1.3, Jongeneelen et al. (1988c), van Rooij et al. (1992, 1994a)
and Borak et al. (2002) have demonstrated that the dermal route can be a major
source of contamination. It is therefore quite feasible that skin contact is either the
main cause of exposure or a major contributor. If the main source of exposure in the
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anode plant is via skin contact, then this would account for the higher comparative
ratio of 1-OHP levels in urine for the anode plant, which were almost 40 times
higher than the reconstruction area, relative to the air levels where the difference was
a factor of two. If the source of contamination is via skin contact with the coal-tar
pitch, this becomes a quite feasible scenario, as this contact cannot be evaluated via
air monitoring. Jongeneelen (1992, 1993) developed a biological exposure index
(BEI) that relates to the present occupational exposure limits for CTPVs (0.2 mg/m3
BSM and/or 2 µg/m3 BaP), and which was dependent on industry type and pyrene
content of the exposure. This was determined to be 4.9 µmol/mol cr for aluminium
workers. In a graphite electrode producing plant in Germany, the level suggested was
21 µmol/mole cr (Angerer et al., 1997). If the BEI developed from the Jongeneelen
equation (1992, 1993) for the aluminium industry is considered here, there is a
noticeable inconsistency. The equation value of 4.9 µmol/mol cr was calculated from
the 0.2 mg/m3 BSF exposure standard; assuming linearity, a median value of 0.054
mg/m3 in the reconstruction area personal air BSF monitoring results would be
expected to be in the vicinity of 1.3 µmol/mol cr. However, it is only 0.17 µmol/mol
cr. This can be readily explained as the result of effective use of respiratory
protection, but what of the result for the anode plant? Here the personal air BSF
monitoring results were 0.036 mg/m3 and the expected 1-OHP result should be in the
vicinity of 0.88 µmol/mol cr or even lower, given the use of respiratory protection.
This is not the case, as the resultant median level is 6.62 µmol/mol cr, suggesting
poor alignment and the possibility of exposure via a route other than inhalation. To
further investigate this line of thought, it would be advantageous to look more
closely at exposure results within the subgroups of the anode plant, i.e. forming and
non-forming areas, as the potential for skin contact presents more readily in the
forming area.
5.1.2 Exposures compared between forming and non-forming areas of
the anode plant of a prebake smelter
Within the anode plant, the median 1-OHP in urine result for workers from the
forming area was 14.20 µmol/mol cr (range 2.02–33.44), more than three times
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higher than those from the non-forming area, with a median of 4.11 µmol/mol cr
(range 0.09–26.99) (p < 0.001).
There are two main types of skin contact: contact with the fume and contact with the
actual product, e.g. paste used for manufacturing the anode. Contact with PAHs >4
rings in the gaseous phase in this study will be limited due to the low levels
identified in the initial monitoring as detailed in section 3.5.1.1. The potential for
fume contact is greatest in areas within the anode plant where elevated fume levels
exist. One regular task involving increased fume contact is associated with the
clearing of blockages or poor flow of paste from the conveyor onto the vibrator plate
associated with the anode former. To reduce the potential for paste going to waste,
the task is undertaken whilst the paste is still being fed to the vibration plate. The hot
paste emits a substantial amount of fume and, due to the nature of the task, the
operator must stand close to the plate to clear it with a long spatula-type tool. Despite
wearing a respirator, balaclava (optional) and gloves, there are still areas around the
face, neck and forearms that are exposed to the fume, hence there is potential for
fume-skin contact. The task duration varies from 2–10 minutes, depending on the
nature of the blockage, and can be required to be undertaken up to six times per shift.
Static and personal air monitoring within the forming area has shown that fume
levels around the former are elevated and, depending on the amount of time spent in
this area, there is a potential for additional skin absorption. Discussions with the
operators in the forming area have provided anecdotal evidence that cases of
phototoxicity, which results in delayed erythema and skin pain (known as ‘pitch
burn’), are more prevalent when working in this area of the plant, thus indicating
higher levels of skin contact. In a study of the relative impact of skin contact, it was
shown that after only 30 minutes of skin contact the dose level of ultraviolet
radiation required to produce skin reddening was halved (Diette et al., 1983). The
recording of the occurrence of pitch burn was recommended as a potential additional
qualitative measure of exposure of workers in the plant.
Review of the personal BSF in air results compared with the 1-OHP urinary results
and the Jongeneelen (1992, 1993) equation again shows an inconsistency with the
forming area BSF 0.046 mg/m3 – expected 1.13 µmol/mol cr (14.20 µmol/mol cr,
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actual) – and the non-forming area BSF 0.028 mg/m3 – expected 0.69 µmol/mol cr
(4.11 µmol/mol cr, actual).
Within the non-forming areas of the anode plant, such as the bake furnaces, the
mezzanine floor and the raw materials area, fume levels were quite low. The low
levels obtained in historic monitoring were used in the past as the justification of the
non-mandatory respiratory protection policy in these areas. Routine monitoring has
indicated that this has not changed. Both static and personal BSF air monitoring
collected as part of this study confirmed that PAH levels in the bake furnaces remain
low.
Skin contact associated with the paste is the second potential area of concern. This
can occur in several of the tasks associated with plant maintenance and also process
intervention where a blockage or equipment failure has occurred. Preventive and
breakdown maintenance occurs on a regular basis, requiring maintenance workers to
access the plant equipment to perform repairs. Where equipment has not been
cleaned prior to this access, maintenance workers have a much higher potential for
contact with the product and skin contamination. The longer the paste is allowed to
remain in contact with the skin and is not washed off, the higher the levels of PAHs
that are absorbed through the skin (ATSDR, 1995). Tasks such as the cleaning of the
fume-extraction ductwork, where thick tar deposits collect and are manually
shovelled out into wheelbarrows, or maintenance of the fume-extraction beds, which
requires entry into an enclosed space that may contain contaminated dust, are tasks
providing ample opportunity for skin contamination.
A fume-extraction system was installed to remove the fume from the main sources
around the forming area of the anode plant and the levels of fume at these locations
have been reduced. However, a consequence of this extraction system is the
concentration and condensation of the fume into the exhaust ventilation ductwork,
which requires the manual intervention of the production operators for cleaning; this
produces a potentially hazardous skin exposure scenario which previously did not
exist. This is also the case for cleaning of the fume bed as described above.
Ironically, a control mechanism for fume in air has solved one exposure issue, but
created opportunity for exposure via a different route. The latter was unlikely to be
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identified, as only air sampling was undertaken as part of the site’s monitoring
program. This is an important lesson that is often overlooked in the design of control
systems. Once a contaminant is removed from a location by some process, it is
important to note how the resulting waste product is presented and how it is to be
dealt with to avoid further contamination of individuals and/or the environment.
Whilst there are tasks and scenarios within the forming area of the anode plant where
the potential for skin contamination exists, there are fewer associated within the
reconstruction area. This does not necessarily translate to lower exposures. Levels of
BSF in the personal breathing zone of the reconstruction area workers were higher
than in workers from the anode plant, but the average level of 1-OHP in their urine
was lower. The task of painting pitch on the walls of the cell does present as a
possible avenue of significant exposure, but the strict adherence of the workers to the
use of full-faced respirators and impermeable coveralls for this task has effectively
reduced the dose by minimising opportunities for direct contact with the pitch and
fume.
Ingestion is also a potential route of exposure to be considered. The opportunities for
ingestion mainly occur as a secondary transfer after cross-contamination, e.g.
contaminated hands transferring to food or cigarettes. The comparison between
smoking and non-smoking groups did show a statistically significant difference at
both the pre-shift and post-shift time-points. Reflecting on the reviewed literature
relating to the low levels of contribution from cigarette smoking to 1-OHP levels in
urine (section 2.4), it is unlikely that this was limited to PAH content of the
cigarettes, and the additional contribution from ingestion of contamination on
cigarettes cannot be ruled out. However, further analysis utilising multivariate
regression models did not demonstrate that smoking substantially confounded
relationships between personal air BSF and urinary 1-OHP levels. Contamination of
food products was possible, and there were instances when workers were observed
not following the site’s hygiene protocols prior to food consumption. Although this
was not assessed quantitatively in this study, anecdotal information was obtained
from supervisors and employees who indicated the majority of workers in the areas
of exposure risk did follow the protocol.
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Overall general hygiene is an area where improvements can be made to reduce levels
of potential contact by ensuring the skin is washed clean as soon as possible
following work exposure, and clothing is kept clean by the use of impermeable
coveralls or contaminated clothing is changed regularly. The utilisation of a
segregated clean/dirty change-house facility similar to that used in the lead industry
would be of value, and the cleaning of equipment before maintenance would also
potentially reduce contact opportunities.
5.1.3 Impact of unscheduled process interactions
When breakdown maintenance or repairs are required, there is less opportunity to
prepare and the contact levels can be higher, as was demonstrated in the case of the
paste dig-out described in section 3.6.1. This scenario does flag a very important
issue in relation to plant reliability. Whilst these situations are not common in a well
maintained and operated plant, if a major plant breakdown does occur that results in
an increased level of intervention between the operators and the plant equipment,
there is a higher potential for exposure. This is particularly the case in a continuousoperation process, where a plant outage can result in process disruptions further
down the line. Data obtained from a batch-plant process in the UK described in
section 5.4, along with anecdotal information from other plants in the Australasian
region, highlight the issues associated with the continuous-process type of plant. A
batch process can be more readily stopped and the necessary maintenance
undertaken with additional time to prepare for an outage and less pressure to return it
to service. Where the interruption is associated with coal-tar pitch in a hot liquefied
or paste state, this can be further exacerbated. If the product is allowed to cool, it can
solidify, and a 2–3 hour cleanout of a conveyor chute or pipework can be magnified
to an outage lasting several days, with significant loss of production and disruption
of downstream processes within the smelter. Hence, there is a strong incentive to
intervene and clean it out as soon as possible. Due to the nature of the process and
equipment, these scenarios usually occur in enclosed areas and, as the product is still
warm, the level of volatiles being emitted can be high. This type of interaction can
result in increased skin contact due to time constraints and, consequently, reduced
opportunities to clean the product off the skin and clothing. If strict guidelines are
106
not in place and adhered to, the pressure to get the fault corrected as soon as possible
to minimise the flow-on effect can be manifested in the deterioration or short-cutting
of safe operating procedures.
It is important that unplanned people-process interventions must be kept to an
absolute minimum to reduce this risk when individuals must place themselves in a
position of direct contact with the pitch paste. Furthermore, when this becomes
inevitable, it is crucial that strict procedures and guidelines are implemented to
minimise any impact on the individual.
5.1.4 Personal protective equipment
Whilst the preferred methods for exposure reduction are the higher levels within the
hierarchy of controls, inevitably personal protective equipment will be utilised as a
mitigating control. This is particularly true where an engineering control has a lag
time associated with the provision of budget and resources to implement. It was
identified during the study that as there were a number of different tasks and
associated exposures requiring different levels and combinations of PPE, it would be
useful to establish a PPE matrix to assist with the selection of the appropriate PPE.
Utilising the initial results, task exposures were rated using the following criteria
based on the 1-hydroxypyrene guidance level for biological and the ACGIH
occupational exposure level for air monitoring, depending on whether the exposure
was via skin, inhalation or both.
•
1=High (> 4.9 µmol/mol cr or > 0.2mg/m3 BSF),
•
2=Medium (<4.9 µmol/mol cr >2.5 µmol/mol cr or,<0.2mg/m3>0.1mg/m3
BSF) or
•
3=Low (<2.5 µmol/mol or <0.1mg/m3 BSF).
In addition, a frequency or duration of exposure component was also included and
considered when determining the PPE required. Also included in the matrix was a
column that identified whether showering was mandated immediately on completion
of the task. This matrix whilst initially developed by a specific working group
became the accountability of the green carbon employees and leadership team and it
has been their responsibility to maintain and update the matrix over the years as tasks
or conditions change. The most recent version is included in appendix 7.
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Given that skin contact is another potential significant exposure route, it is important
to determine what PPE is used in this context and its effectiveness. For all but the
very dirty tasks, the standard apparel in the plant has been long-sleeved cotton drill
shirts, long trousers, a cotton balaclava, light leather riggers gloves, safety glasses
and a hard hat (Figure 3.14). Depending on the task and location, a half-face
negative-pressure cartridge respirator also has been utilised. Cotton drill provides
little protection from CTPVs and, when in contact with liquid pitch or paste residue,
can absorb and retain these harmful substances which then remain in contact with the
skin for extended periods of time (Masek, Jach, & Kandus, 1972). This increases the
absorption potential and maintains exposure long after the worker has left the work
area. Such contamination from clothing and other pieces of equipment has not been
quantified at this stage, but it is recognised as an area of concern. The site at which
the study was undertaken did have a policy whereby all workers’ clothing was
deposited in a specified area at the end of the shift and was laundered by the
company; however, at the time this was not a requirement for contractor employees.
Contaminated work articles, such as clothing, must not be allowed to be taken home
or worn off-site, as this can create the possibility of cross-contamination of nonoccupational clothing or other individuals from direct contact.
Riggers gloves are quite porous and will readily absorb the pitch and associated PAH
compounds. Also, they are short, allowing the wrists and lower forearm to become
exposed (particularly when working overhead) as well as providing an area around
the wrists for the larger particulate to fall into and become entrapped. This could
result in increased close skin contact whilst the worker believes they are being
protected, and prolonged periods of exposure due to a false sense of protection.
Anecdotal evidence from a trial at a similar prebake smelter (Wilson, 2002)
indicated that the use of a water-based barrier cream had the potential to reduce
absorption of PAHs into the skin and could be used as a further control. However, it
was noted that in an animal study (Prior, 1996), results indicated fat-based barrier
creams facilitated the absorption of pyrene and should be avoided.
When considering respiratory protection in areas where elevated fume levels may be
present, full-face rather than half-face mask respirators should be employed so as to
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provide additional protection for the face and eyes from fume and fine particulate,
and to reduce the amount of exposed skin. PPE was investigated as a potential
correlate of 1-OHP and was considered to have an association based on the results of
the Mann-Whitney analysis, but showed only negligible association after adjustment
for smoking and BSF. With respect to the association of BSF and 1-OHP there was
some minor confounding associated with smoking and PPE, particularly in relation
to the anode plant non-forming area. The Mann-Whitney analysis also identified an
association between smoking and 1-OHP in the pre- and post-shift comparisons. In
both cases, there were significant increases associated with the smokers in the group.
This was dissimilar to the study by Borak et al. (2002) in which levels of 1-OHP in
urine did not differ significantly between smokers and non-smokers, but did align
with results of other studies (van Rooij et al., 1994b; Gündell & Angerer et al., 1999;
Jongeneelen, 2001) in which there were significant contributions from smoking to
urinary 1-OHP levels. It should be noted that the levels in these studies were quite
low (<1.0 µmol/mol cr) and a small change would be more readily observed
compared to the larger median values detected in this study, where the range was
0.001–33.44 µmol/mol cr. As highlighted in section 2.4, an average daily
consumption of approximately 20 cigarettes was required to bring the levels of 1OHP in urine to 200 ng/L (Buratti et al., 2000). These levels would be difficult to
detect in the study samples, where post-shift sample results were an order of
magnitude higher. Hence, it is quite possible that the increase is not related to the
absorption of pyrene from the cigarette smoke, but more likely from crosscontamination of the cigarettes with coal-tar products arising from poor hygiene
practices of the individuals as they smoke.
5.1.5 Assessment of the relationship between BSF in personal air
samples and 1-OHP in urine
Paired samples of personal BSF air monitoring and 1-OHP in urine monitoring were
obtained to look for a correlation between PAH exposure and 1-OHP concentrations
in urine.
The regression analysis of the 1-OHP in urine and BSF in personal air samples
showed a poor adjusted R2 value in the four models examined. Of the adjusted
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models, BSF in the combined group model and anode plant forming area models also
accounted for less than 1% of the variation in 1-OHP levels in urine. Adjusted R2
values from the anode plant and non-forming area regression models were at 3.2%
and 11.4%, respectively.
Thus, there appears to be no predictive relationship
between personal air monitoring for the BSF and 1-OHP in urine of workers
involved with tasks in the prebake smelter in this study. This suggests that the use of
BSF as a stand-alone measure of exposure in the anode plant of the prebake smelter
is a poor indicator of actual total exposure. Also, there is a strong indication that the
main route of exposure in the anode plant is dermal and not via inhalation. This
aligns with studies in which the dermal contribution to total exposure was estimated
to be more than three times higher than intake via the respiratory tract and estimated
to be 51% in another (van Rooij et al., 1992, 1993a). In their study on paving
workers, McClean et al. (2004) estimated that dermal exposure was eight times the
impact of inhalation exposure. Similar results were reported by Borak et al. (2002) in
their study of creosote facility workers. Therefore, significant dermal contribution to
total exposure is not unexpected considering the potential for skin contact across the
anode plant.
The regression analysis of the personal air BSF monitoring levels and urine 1-OHP
levels are in line with the findings of other studies which showed that the relation
between air monitoring data and biological monitoring data was not strong (Unwin,
Cocker, Scobbie, & Chambers, 2006; Jongeneelen, Leeuwan et al. 1990). In a study
undertaken in a carbon anode plant of a prebake smelter, van Rooij et al. (1992) also
found that the increase in 1-OHP over a 5-day work-week did not correlate well with
air concentrations (r = 0.18). In contrast, there have been studies that have indicated
a good, if not predictive, correlation between the 1-OHP and air levels of PAH; Wu
et al. (1998), studying workers in a coke oven, reported r = 0.70 (p = 0.001), Buchet,
Gennart et al. (1992) also in a coke oven reported (r = 0.72, p<0.0001) and Tjoe Ny
et al. (1993), conducting research in an aluminium plant, reported r = 0.84 (p =
0.0001). It is important to note that the coke oven exposures were air exposures and
that in the Wu study it was acknowledged that there was a poor respiratory
protection practise. The Tjoe Ny et al. (1993) study was based on a Söderberg
technology potroom, where once again the main route of exposure to PAH was
predominately air-centred.
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5.2
Strengths and limitations
In the investigation of exposure in industry, particularly in the area of biological
monitoring, one of the most difficult aspects is the ability to obtain participation
from employees in the workplace. Average participation in this study was 83%
which provided a solid basis for the investigation. Whilst it would have been ideal to
obtain 100% participation in the study from the cohorts, average participation was
still quite high. Participation rates were lowest for analytical laboratory and human
resources workers (50%) in the non-production group. Members of this group,
chosen specifically for their non-involvement in any processes associated with PAH
exposure, were unlikely to have the same level of interest in the study as those
workers with potential for exposure. As all of the results for this control group were
below the level of detection, the impact of a lower participation rate on the study was
minimal. The monitoring program was developed to meet the requirements outlined
in the international occupational hygiene texts and guidance literature. Monitoring
was conducted over the period of February 2002 to September 2004 and this enabled
the key processes and associated tasks undertaken by the work groups to be covered
within the monitoring program.
A total of 166 sets of pre- and post-shift urine samples were collected from the
cohort for analysis of 1-OHP. Of these, 20 were not within the creatinine range
specified by the method’s guideline and 18 were missing the post-shift sample, and
were therefore excluded from the analysis. From the control group, 24 sets of
samples were collected. In addition, 167 personal air samples and 249 static air
samples were collected and analysed for BSF, and there were 58 matched sets of 1OHP urine results with a corresponding personal BSF in air result.
Monitoring of 1-OHP on a pre-shift and post-shift basis could have been improved
by sampling at the beginning and end of each day of the full-shift rotation to ensure
peaks were not missed. Unfortunately, the adoption of this approach would have
increased the cost of this project beyond the proposed budget to a point where it
would have been unaffordable. However, the adopted approach did meet the
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requirements for biological monitoring as set out in the ACGIH guidelines as
previously discussed in section 3.5.2.1.
There are some limitations to using urinary 1-OHP levels for monitoring purposes,
particularly in relation to the actual biological effect on the body. The measure does
not provide a level with which to quantify risk of cancer to the individual, as the
measure is of a metabolite of a surrogate, non-carcinogenic compound. There are
also some issues of sampling relating to the differing half-life of the excretion rates
for 1-OHP in urine and individual physiological variability. Depending on the timing
of the post-shift 1-OHP sample, it is possible to miss an exposure if it occurs very
early or very late in a shift rotation. In the first case, the 1-OHP may be completely
excreted before the sample is taken and, in the latter, there may not be enough time
for the 1-OHP to have made it through to the urine, resulting in an underestimation.
This issue can be resolved by utilising 24-hour urine sampling or increased
frequency of spot urine sampling, but there are problems with both approaches. The
24-hour sampling was not acceptable to the participants in the study nor would it be
practical as a routine method. Increased spot sampling would dramatically increase
the cost of the sampling program to a point that it would become unviable. Another
limitation of the biological monitoring approach is due to the nature of the sampling.
There are workplaces where the sampling of urine is not readily accepted due to
privacy or cultural issues, a perception that it is an invasive procedure and, in some
cases, because of mistrust of management. With the introduction of drug testing at
the workplace, this can be perceived as a ‘test by stealth’, i.e. what else are they
going to test for once they have the sample? In this study, the inclusion of a clause in
the participants’ ‘permission to sample’ authorisation form specifying that no other
testing was being authorised was seen by the participants as an important part of
their willingness to take part in the monitoring program.
In the initial development of this project, there was only limited involvement of a
statistician in the study design. As a consequence, the author spent significant
additional time redesigning sampling and data collection protocols to more
comprehensively address the study hypotheses. It would have been prudent for the
advice of a statistician to be sought at the beginning of the project as part of the
planning process in order to more accurately determine sampling requirements for
112
the different groups and avoid re-work associated with an inappropriate statistical
analysis plan.
For completeness, it would have been very useful to have included the exposure
levels of one other SEG associated with the bake-out of new cells on the reduction
line of the prebake smelter as part of this study. This was another group within the
smelter with known exposure to PAHs whilst undertaking one of their tasks. The
exposure is predominantly via inhalation in the reduction lines when cells are first
brought on-line and are exposed to high temperatures. There is no physical contact
with coal-tar pitch during the operation, but monitoring could have provided some
additional information in relation to exposure and dermal adsorption of fume at high
temperatures. Unfortunately, inclusion of this group would have extended the time
and cost beyond that which had been determined to be appropriate.
The level to which the results of this study manifest in other smelters or, for that
matter, in other industries that utilise coal-tar pitch, is obviously a function of the
processes employed and the controls utilised. The results do bring into question the
applicability and validity of using airborne monitoring for exposure to PAHs as the
only method of assessment without some form of biological monitoring as an
adjunct. It has been known for centuries that skin contact with coal-tar byproducts
has the potential to generate carcinomas of the skin and, in more recent times, that
PAHs are readily absorbed through the skin and into other key organs such as the
lungs and liver. So, it should not come as a surprise that in an industry where there is
a potential for this contact to occur there may be exposures that are not being
quantified. Unwin et al. (2006) reviewed exposures to PAHs across 19 industries in
the United Kingdom to determine if one or more target analytes were suitable as
markers for assessing total exposure to PAHs. Whilst this study used BSF in air,
rather than BaP as used by Unwin et al. (2006), the two parameters are both air
measures that align well. Initially, the air and the biological monitoring did not
correlate in the UK study (R2 = 0.008). However, when the industries that utilised
respiratory protection were taken out, the correlation improved dramatically (R2 =
0.77). The non-forming area of the anode plant was the only area of the plant where
PPE was not mandatory across the board and workers had some discretion as to
whether it was worn. It was in this section of the plant for which a potential
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confounding effect was noticed from the regression B-coefficients for BSF (-27.7
unadjusted; -31.3 adjusted). Also, there was an increase in the predictability of the
overall percentage variance in the 1-OHP, adjusted R2; however, it was not large
(0.00 unadjusted, 11.4 adjusted).
Exposure within the aluminium smelting industries requires careful assessment and
review to ensure that all pathways of potential exposure are identified and some form
of quantitative assessment is put in place to enable the determination either directly
or indirectly of the relative contributions to the dose. This is where the initial walkthrough survey plays a pivotal role in the development of the monitoring plan for a
site. When it can be seen that there is potential for PAH-containing ingredients or
product to come in contact with the skin, then some form of biological monitoring
must be considered. A question that does arise is why there has not been more
activity in the application of this form of measurement. There have been a variety of
reasons put forward in the past; one of the most prominent is that 1-OHP is not a
measure of the actual carcinogens, but of a metabolite of pyrene which does not
provide significant information in relation to potential carcinogenic impact. This is
true, but the use of biological markers to gauge overall exposure can prove to be of
immeasurable value in relation to the effectiveness of controls and interventions. The
sampling of urine is less intrusive than blood sampling, and there are now increasing
numbers of analytical laboratories that are competent in analysis of 1-OHP. The
approach of incorporating biological monitoring into the monitoring program will
capture the contribution of skin and/or ingestion exposures.
5.3
Process intervention as a result of early findings
Initial 1-OHP monitoring results of the green carbon maintenance group averaged
5.49 µmole/mole cr (range 0.39-27.0), which indicated that more than half of the
exposures were above the guideline value of 4.9 µmole/mole cr adopted for the site.
On the strength of this, site and area management teams decided that, rather than
wait until extensive data analysis was completed, improvement opportunities should
be implemented and trialled as soon as possible. A review of work practices
indicated that the most likely source of contamination was arising from the workers’
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contact with the paste products on the equipment, as most of their work was being
done whilst the plant was off-line. To try to reduce this contact, additional controls
were employed. These included changes to the cleanliness and condition of the plant
equipment prior to hand over to maintenance workers, improved PPE such as
impermeable gloves and coveralls (Figure 5.1), use of water-based barrier creams
and re-emphasis in training on the need to remove contamination from skin as soon
as possible, which sometimes meant showering numerous times during the shift for
particularly dirty jobs. Most of the controls were readily adopted, but the use of
impermeable disposable coveralls was very unpopular due to the warm subtropical
climate.
A compromise was struck such that the coveralls were required to be worn only for
dirty tasks, and semi-impermeable coveralls could be substituted for lesscontaminated jobs. If the equipment was well cleaned prior to commencement, the
use of the coveralls would be voluntary. A matrix, developed in consultation with the
workers, identified the tasks to be undertaken, the level of clean required and the
necessary PPE appropriate for the task. To achieve a higher level of cleanliness, a
contractor was employed to use small quantities of high-pressure water on plant
equipment prior to maintenance.
It became apparent very soon after the changes were implemented that they were
having an impact. An initial indicator that things were going well was that reported
cases of pitch burn became rare within this group and eventually ceased. Also, the
reduction of the level of contamination on the work clothes became visibly
noticeable. Monitoring, undertaken in two subsequent batches six months apart,
showed a substantial decrease in the median and range of the levels of 1-OHP in
urine. Discussions with the occupational hygiene team at the site revealed that the
results continued to decline and have been maintained below the site’s guidance
level for 1-OHP.
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Figure 5.1: Mechanical equipment technician performing maintenance on the anode
former (Photograph taken after implementation of several changes to the requirement
of PPE; note use of Tyvek® coveralls and impermeable gloves)
5.4
Additional key points
Does a BEL have value in quantifying risk considering the variation of levels
and ratios of PAH: pyrene in contaminants?
Consideration of the use of 1-OHP exposure limits as a monitoring tool is a complex
issue. As detailed in section 2.3.2, 1-OHP is a metabolite of a component of the
PAHs normally found in coal-tar pitch. The ratio of pyrene to other PAHs in coal-tar
pitch is variable between suppliers; this impacts the relative concentration of 1-OHP
in urine from exposed workers. In addition to this, the temperatures associated with
the processes in the anode plant vary from the moderately low levels of the paste
(<100°C) in reconstruction and the front section of the anode plant (160–200°C) to
the elevated temperatures in the anode furnace area (>1000°C). The different PAHs
116
have varying vapour pressures and are likely to be driven off at different
temperatures across the process, again impacting on the total CTPV to pyrene ratio
and, consequently, concentration of 1-OHP in urine.
The practical implication of this in an aluminium smelter (or other industry) is that if
the composition of coal-tar pitch varies due to manufacture or change of supplier or
even location within the plant, there is a potential to impact on the validity of any
chosen biological exposure limit (BEL) guideline. This, in turn, would mean that a
new BEL would have to be calculated for each scenario, which is cumbersome and
impractical. This does not mean that the level of 1-OHP in urine cannot be used as a
monitoring tool in an environment where the pyrene to PAH ratio may change
because it is possible to build regular measures of total PAHs to pyrene ratios into
the monitoring process and account for batch differences as required.
Although it would be difficult to maintain an accurate measure of pyrene to PAH
ratio, an average concentration of the exposures in air for a particular site or industry
can be calculated and used to set a target value. This has been done, for example, by
Bjørseth et al. (1978) for the aluminium, coke and iron industries. More recently, the
UK Health and Safety Executive has introduced a benchmark guidance value for
biological monitoring for PAHs based on measurement of end-of-shift urinary 1OHP concentrations (Armstrong et al., 2003).
A level of 4 µmol/mol cr was
recommended, as this value represents the 90th percentile of measurements taken
from industries deemed to have good control. There was only one smelter in this
group of industries that was assessed, which was an anode plant in a small prebake
smelter. The results were quite low, with a mean of 0.72 µmol/mol cr (range 0.25–
2.60). A later study carried out at the same prebake smelter yielded similar results for
an operator SEG with a mean of 1.17 µmol/mol cr (range <0.01–3.76) and
maintainer SEG with a mean of 0.72 µmol/mol cr (range <0.01–5.37) (Jessep, 2007).
The process in the UK anode plant was a batch process compared to the continuous
process in the anode plant of this study, which would account for some of the
difference.
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Initially, adoption of a level such as that developed by Jongeneelen (1992, 1993), 4.9
µmol/mol cr for aluminium workers, provides a relative marker to work to and on
which to base action levels. This can be further refined to match the composition of
the pitch and associated PAHs for the site at a later stage. Looking at the results from
the process intervention discussed in section 5.3, the median 1-OHP urine
concentration was 5.49 µmol/mol cr prior to the control modifications. This was
above the adopted guideline and warranted action. After 18 months the median was
2.36 µmol/mol cr showing a marked improvement. Hence, a form of biological
exposure guideline does add value to the management of exposure to PAHs in the
smelting environment.
Is 1-OHP a valuable tool for the identification of levels of general exposure to
PAHs in a smelting environment?
Yes it is. Often professions or disciplines can become fixated on the requirement of a
value against which to measure and regulate. This prescriptive mindset has been the
approach for many years and, while easy to adopt and administer, it may not be the
most suitable approach for the monitoring and control of PAHs in some industries.
The results of this study suggest that, regardless of exposure route, fluctuations in
observed concentrations of 1-OHP indicative of PAH exposure are more useful in an
OHS context than an absolute concentration limit to determine action levels. This is
where one of the main benefits of monitoring 1-OHP lies. To continue to monitor the
air with the belief that it is providing an accurate representation of exposure to PAHs
in an aluminium smelting environment is misguided and erroneous and, whilst the
monitoring of 1-OHP in urine may not be an accurate measure of biological effect on
an individual, it is far better than continuing with just air monitoring.
How applicable this is to smelters globally will depend on the process being utilised,
i.e. Söderberg or prebake, continuous or batch processes in anode plants, the
technology in place, particularly in relation to extraction systems, human-machine
interactions and process intervention frequency. All of these will vary to some extent
across the industry and sites. As detailed previously, each one of these can have a
significant impact on the route of exposure and eventual dose. What does not alter is
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the fact that if there is a potential for dermal exposure, no matter what the process is,
monitoring the levels in air will not pick up this contribution to the body burden.
There have been numerous studies over the years in environments such as iron
foundries (Hansen et al., 1994; Sherson et al., 1992), graphite electrode-producing
plants (Angerer et al., 1997; Ferreira et al., 1994), road paving (Burgaz et al., 1992),
chimney sweeping (Pavanello et al., 1999) and firefighting (Moen & Øvrebø, 1997),
as well as studies across occupations (Unwin et al., 2006) in which 1-OHP has
proven a useful tool. Despite the absence of a BEI to relate to the utilisation of this
method, it is still a valid and potentially powerful tool.
Is there a point in a multifactorial exposure regime at which BSF estimations
cease to have any occupational relevance, or can they be used only if dermal
exposure is controlled or excluded?
The value of monitoring BSF on its own or as part of a multifactorial exposure
regime within industry is debatable and there are a number of key factors that need
to be considered. If the concern is specifically for the higher level, greater than 4ring PAHs (i.e. the key carcinogenic compounds) then this approach may be flawed
if there is potential for exposure where the lower level PAHs predominate. This was
highlighted by Unwin et al. (2006) in a study over a number of industries that
showed a weak correlation between total PAH and total carcinogenic (4-6 ring)
PAHs (r2 = <<0.1). This was most probably due to the high levels of naphthalene,
the most volatile of the PAHs, which was present at a number of the sites. The
impact in such situations is that a small variation in concentration levels of
toxicologically significant PAHs would be swamped by the higher concentrations of
the lower end PAHs. This can be overcome by undertaking a full scan of the
compounds captured and this approach can add value in profiling the contaminants
in the initial monitoring program. Unfortunately this can be a very expensive option
in the long term as such analysis is costly on a large scale such as in routine
monitoring surveys. In situations such as coke ovens and some aspects of the
aluminium smelting process where exposure to the carcinogenic compounds could
be significant, a better approach would be the monitoring of benzo(a)pyrene. This
compound is a 5-ring PAH which has been shown to correlate well (r2 = 0.97) with
the 4-6 ring compounds (Unwin et al. 2006). Added to this is the similarity in
119
chemical properties with the other 4-6 ring compounds such that changes resulting
from condensation, absorption and evaporation will be mirrored by benzo(a)pyrene.
The monitoring procedure is the same as that for the BSF so no additional equipment
is required.
In the industries where the 4-6 ring compounds are either not present or in very
minor quantities and the main exposures of concern are the lower level PAHs, then
BSF monitoring will be the preferred approach and the benzo(a)pyrene monitoring
of limited value. The United Kingdom Health and Safety Executive (UK HSE) has
not adopted an exposure strategy based on an airborne exposure level to BaP as it
was deemed to be a poor predictive marker for exposure to the 2-4 ring gaseous
compounds which were the largest group of highly exposed workers in the UK.
(HSE, 2003)
There may also be a need for consideration in relation to the epidemiological and
historical value of the monitoring of BSF. This approach has been used for many
decades as the main exposure monitoring tool to profile exposure to PAHs in
industry. There could still be benefit in monitoring BSF where comparisons to
historical data may be required.
There is of course a key assumption being made here that the main route of exposure
is inhalation and that the component of exposure related to skin absorption is
minimal. Where this is not the case then the value of this monitoring approach
diminishes and in some cases may even be irrelevant.
Situations such as
maintenance personnel working on cold equipment contaminated with coal tar pitch
paste, such as in anode plants, have a small risk associated with inhalation exposure
however their risk associated with skin contact can be quite high. Hence there would
be minimal if any value associated with BSF monitoring in this scenario. Similarly in
the situation where a respiratory protection program is in place and no other
engineering modifications can be made (i.e., coke ovens), the benefit achieved by
monitoring air exposures is very limited? In this case biological monitoring will
provide information as to whether the PPE is actually working and would be the
preferred approach. Within the aluminium industry BSF monitoring still has a role to
play in the control of exposures to PAHs, particularly in the early stages of a
program where information relating to the profile and characterisation is required. It
is best suited as a component of a multifactorial monitoring program particularly
when utilised in static monitoring to identify areas of a plant or process where
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fugitive emissions sources may need to be identified but should not be used as the
sole method.
Is skin exposure a major contributor to total body burden at the prebake smelter
in the study?
Yes, this was indicated in the data presented, particularly in the anode plant where
the expected alignment of BSF in air and 1-OHP was poor. The review of the median
results in the forming area using the Mann-Whitney sample tests on those
participants wearing/not wearing overalls was not conclusive but did show a
reduction in the variation of the range (1.28 - 19.46 µmol/mol cr compared to 3.69 –
46.0 µmol/mol cr), where those wearing overalls showed generally lower levels of
exposure. Following on from this, the regression analysis using the skin exposure
questions from the questionnaire also showed some positive association with the 1hydroxypyrene levels, and with an adjusted R2 of 10.2%, the skin aspect cannot be
totally disregarded. From the discussion in section 5.1.1, looking at the results of the
personal BSF in air monitoring and the 1-OHP urinary measurements in light of the
Jongeneelen (1992, 1993) equation, there was again a poor alignment and the
possibility of exposure via a route other than inhalation indicated. Finally, the
improvements achieved by targeting skin exposure in the intervention also supported
the likelihood of exposure via this alternative pathway. Whilst the evidence based on
the empirical data may not be strong for this conclusion, there is without doubt a
robust inferential support of the likelihood of skin being a major contributor to the
body burden. With further investigation based on a targeted skin contamination
assessment program linked into the 1-hydroxypyrene biological monitoring, this
should become clearer.
What are the implications of the inadequacies of the current risk assessment
metrics (in both the past and the future) for the primary aluminium industry and
other occupations where there may be exposure to PAHs?
One of the key aspects of this question comes back to having a thorough
understanding of what the actual exposure profile at a site is. It is not as simple as
saying an industry needs to undertake air monitoring as that is the only OEL in place.
As has been previously discussed, this approach may be totally irrelevant in
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situations where there is minimal air exposure but significant potential for skin
contact. It can also apply in the reverse where skin exposure is limited but inhalation
is the key form of exposure.
Some sectors of the aluminium industry (and other industries) in the past have
focused their attention on the reduction of exposure to airborne PAHs and have
successfully reduced them to levels below the regulatory exposure limits. This has
been the benchmark standard that businesses have sought to achieve and have been
measured against by regulators. The question remains, have they been addressing the
right source of contamination? Without taking into account the issue of ingestion
and/or skin absorption, there is the possibility to build an erroneous risk profile with
a key piece of the jigsaw missing. This has the potential to direct control strategies
and resources towards areas that may not be the key source of exposure. This could
result in the waste of scarce resources, both financial and human and the inadvertent
continued exposure of individuals to a hazardous material.
There is also another side to this for those industries that have been measuring high
total BSF in air which are predominately at the lower level of <4 ring benzoics.
Many regulators mandate stringent health surveillance requirements where potential
exposure to PAHs exists, which are expensive and complex to administer, especially
for small- to medium-sized manufacturers. Where the mixture profile indicates a
presence of the carcinogenic >4 ring compounds, then this is a valid approach but
what of the industries where a high BSF in air is as a result of high levels of
naphthalene or similar compound without the same toxicity? Should they also be
encumbered with the same requirements of an industry such as those that use coal tar
pitch and higher levels of compounds such as benzo(a)pyrene? With this
consideration and in light of growing intolerance of the public at large to any
exposures to known carcinogens and the acceptance in principal by many industries
and regulators to the ALARP principal, it is now a timely juncture for the review of
the approach to the management of PAH exposures and the consideration of
alternative risk assessment methodologies.
In planning a risk assessment there needs to be an accurate mapping of the process
covering all potential routes of exposure. This will mean personal air monitoring,
with the resultant contaminants profiled to enable a characterisation of the
components and static air monitoring of the process to identify if there is a particular
emission source and to verify engineering control efficiency. Biological monitoring
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also needs to be employed initially to determine the potential for exposure via
ingestion or skin absorption, and where personal protective equipment is used as a
critical control, to determine its ongoing effectiveness. This initial extensive analysis
should provide the basis of information needed to determine the extent of further
monitoring and ascertain whether an extensive monitoring and medical surveillance
program needs to be employed. This approach should be adopted for any industries
utilising compounds containing PAHs in their process. It may well be the case for
many of these industries that this approach confirms that there are no issues with
their current risk assessments and controls but without testing all potential routes of
exposure when dealing with PAHs it will be difficult to remain confident that
exposure is not occurring in these areas.
5.5
Future research
The results of this study support the likelihood that a significant dose of PAHs is due
to skin absorption in the anode plant of the prebake aluminium smelter, but there was
no attempt made to quantify the amount. In studies by van Rooij et al. (1992, 1993b),
McClean et al. (2004) and Borak et al. (2002), the dermal contribution was
investigated in smelting and other industries. It would be useful to better quantify
this component in a prebake smelter via the use of skin patches. These could be
placed on areas of the skin where there is suspected exposure such as the wrists, face
and neck region. Monitored in conjunction with BSF and 1-hydroxypyrene, it would
provide a better quantification of the impact of skin exposure on total body burden.
Also, the possible impact of the thermal environment on the absorption rate of PAHs
through the skin requires further investigation. Anecdotal evidence (A. Riley,
personal communication, 2004) from an internal skin mapping program, as described
in section 2.1.3, indicated the presence of increased contamination on the skin in
areas of high sweat production. The plant in this study was located in a subtropical
climate and, as a result, most of the workers were acclimatised to the heat. One of
the ways in which the body manifests this acclimatisation is that there is an increase
in the production of sweat, hence the question as to whether this results in additional
absorption due to increased activity of the sweat glands needs to be addressed.
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The potential transfer of contamination from PAH-soiled clothing to skin and the
effectiveness of current laundering processes needs to be investigated further to
determine the level of cross-contamination that may be occurring. An alternative
parent-metabolite pairing – BaP and 3-hydroxybenzo[a]pyrene – was the subject of a
study carried out in a selection of industries in France; results showed this to be a
potentially useful method for determining a biological limit marker, as the parent
compound BaP is a known carcinogen (Lafontaine & Gendre, 2003). Lafontaine and
Gendre’s (2003) brief report recommended the determination of such a limit by
correlating back to the French airborne exposure limit of 150 ng/m3. This has the
potential to provide a more accurate quantification of actual carcinogenic load on the
body and the method should be further researched.
The relationship between biomarkers and cancer has been the subject of several
animal studies focussed on DNA adducts. Some of the markers investigated include
DNA or protein adducts (dell’Omo & Lauwerys, 1993), cytogenic markers (e.g.
micronuclei, chromosomal aberrations, sister chromatid exchanges) (Tucker &
Preston, 1996) and cells with a high frequency of sister chromatid exchange. Some
of these markers are indicative of an early biological effect, although it may not be
permanent and may not have further consequences (van Delft et al., 1998). These
tests therefore have the potential to determine a direct biological effect on the body
and, consequently, be of greater value in determining the actual carcinogenic risk.
Early testing has been carried out utilising blood sampling, which is regarded as a
more invasive monitoring method than urine sampling. There is potential to utilise
urine sampling for this testing; however, the method requires further development.
There are numerous methods for the assessment of exposure of individuals to PAHs
in various stages of development, some of which have the potential to become very
powerful tools for the investigator. At the moment, the use of 1-OHP in urine
appears to be the most practical and, importantly, is readily accepted by the target
subjects. It does have some limitations, as outlined above, but based on the results of
this study, it is a substantial improvement on the previous approach of monitoring air
exposure alone.
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5.6
Recommendations for control measures
With respect to on-site management of PAHs, there was potential for improvements
identified during the study and these are outlined below. It should be noted that the
site at which the study was undertaken has adopted all of the following
recommendations. In order to implement some controls, there needs to be
modification or extension of site policies in some areas. When developing controls
for the occupational environment, the hierarchy of OHS hazard controls is always
referred to for order of preference. Wherever possible, the contaminant or its cause
should be eliminated. When that is not possible, substitution of the compound is next
preferred. Engineering solutions are next in line, followed by administrative controls.
Use of PPE is always the last method of control to be employed and only when the
higher levels of control are not practical or as a short-term, interim measure.
Consultation with the employees working in the areas is an important aspect when
looking at control options. Their familiarity with the process, the plant and its
idiosyncrasies can prove invaluable and should always be part of the control
identification process. From observations made during the study, there are additional
controls that could be employed to reduce the levels of exposure to PAHs in the
prebake smelter.
5.6.1 Engineering
As previously outlined in section 5.1.2, key exposures exist in relation to the
maintenance of the fume-extraction system. The system requires modification to
prevent the CTPVs recondensing in the pipe work leading to exposure associated
with the clean-out process. The injection of fine coke particulate into the airstream
has been utilised at other smelters successfully and could be introduced at this site.
Redesign of the fume-extraction system such that it could maintain balance would
also reduce the manual intervention associated with its operation.
The overall design of the vibration plate on the line 1 and 2 former appears to be
flawed, as it is continually blocking and hence warrants a major redesign. In the
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interim, the lid opening of the vibration plate should be redesigned to prevent
exposure of the operator when cleaning is required, and the cleaning task should be
undertaken while there is no paste flowing through the system.
Process intervention must be minimised wherever possible with the key being
process stability and control.
5.6.2 Administrative
As discussed in sections 2.3.2 and 2.5, the variability of the coal tar pitch being used
the ratio of pyrene to BaP and other carcinogenic PAHs in the different mixtures of
PAH, the temperature of the different stages of the process and the personal
physiological variation make it particularly difficult to allocate a definitive biological
exposure index for 1-hydroxypyrene. This is compounded by the limitations of the
air monitoring process to address all the potential exposure routes. Hence, due to the
carcinogenic nature of the contaminant it would be prudent to ensure that the “as low
as is reasonably practical” (ALARP) principal is applied for any exposures, rather
than relying solely on exposure limits.
Within the forming area of the plant, there exists a ‘former technician’ subgroup of
workers, whose role and tasks are outlined in section 3.3.1.1. These workers spend
all of their time in the forming area of the plant and are exposed at higher levels for
the majority of their four-day shift rotation. As a consequence, there is the potential
for not all of the absorbed contaminants to be excreted before re-exposure, resulting
in a cumulative effect by the end of the four-day rotation. Under the current
operational approach, when they return after their days off, they have the opportunity
to be placed in a lower-exposure area of the plant, such as the mezzanine floor or
raw materials area or, for those more experienced, the control room. This presents
site management with an opportunity to reduce the exposure via an administrative
control. Rather than keeping an individual in this role for all four days, s/he could
move through the other roles during the one rotation, and hence reduce the body
burden and allow full excretion of PAHs before re-exposure. This would reduce the
potential for PAHs to accumulate in the body to any significant levels. There would
be a corollary associated with the training and competence of the employees. This
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approach would obviously be dependent on crew members being able to carry out all
tasks associated with the green carbon plant. This is achievable, but would take time
and would rely on a stable workforce with effective training programs to be
implemented and maintained. Flexibility needs to be built into the shift roster to
enable this training and cover for individuals on recreation and sick leave resulting in
potentially one more employee per crew. This again is likely to have an economic
impact on the process, but would assist with fatigue management and allow
individuals more flexibility in their work and the ability to reduce the time that is
taken before they break for a shower to remove skin contamination, which is
potentially a major contributor to their exposure.
All employees and contractors who may come in contact with PAHs must undertake
awareness training in relation to the nature of PAHs, their health impacts and the
controls associated with their management.
Procedures should be established to increase the general cleaning of plant and
equipment to prevent build-up of coal-tar pitch products and minimise the risk of
gross skin contamination when maintenance must be carried out.
A clean/dirty change house facility similar to that employed by the lead industry
needs to be implemented and located close to the anode plant. Individuals must be
encouraged to clean off any skin contamination as soon as possible and report any
occurrence of pitch burn to supervisory or occupational health support teams. As
discussed in section 2.1.3, access to a low-level purple UV light and mirror has
proven to be a useful aid in identifying skin contamination. The level of UV light
emitted is not high enough to initiate pitch burn, but causes the contaminated area to
fluoresce, which assists with identifying areas of the skin that require particular
attention.
Employees must shower prior to leaving the site, and contaminated
clothing must not be allowed to be worn off-site, nor should it be washed with
domestic clothing at the employees’ homes due to the potential for crosscontamination with other clothing. Grossly contaminated clothing can result in
exposure of other family members. Consequently, all clothing worn by plant and
contractor employees working in the green carbon area must remain on-site and be
laundered.
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5.6.3 Personal protective equipment
Some additional modification in relation to the required level of PPE is necessary.
Where there is potential for the worker to come in contact with coal-tar pitch and/or
its volatiles, a barrier must be established. This means that cotton drill clothing is not
appropriate in some of the work areas, and the use of semi-permeable and
impermeable coveralls may need to be adopted for some tasks. Also, riggers gloves
are inappropriate for some situations due to their permeable nature and short length.
A longer glove (to mid-forearm) impermeable to coal-tar pitch products should be
utilised. Finally, where there is a high level of fume, half-face mask respirators
should be replaced with full-face mask respirators to provide additional protection
for the skin of the face. Water-based barrier creams should be utilised prior to
exposure to minimise uptake and facilitate the cleaning process. Sunscreens should
be employed at the end of the shift to aid in the prevention of pitch burn of the
photosensitised skin.
A simple task-and-PPE matrix needs to be developed (see section 5.1.4) based on the
risk of exposure to PAHs of the individual when carrying out any particular task.
This will provide guidance for new employees and those unfamiliar with the task to
which they have been assigned. Caution must be exercised when utilising high levels
of PPE in the subtropical climate, as this has the potential to introduce an elevated
risk of heat stress.
5.6.4 Occupational health practice
Medical surveillance should be carried out on individuals whose exposure is equal to
or greater than the guidelines set by the company or the regulatory authorities
(whichever is more stringent). The surveillance program should contain as a
minimum:
•
occupational history and qualitative estimation of exposures to pitch
(where quantitative results are unavailable);
•
medical history;
128
•
physical examination; and
•
urinalysis.
In addition to this, employees should have the opportunity to discuss their questions
or concerns with an occupational physician and a professional occupational
hygienist.
5.6.5 Monitoring
It has been shown that exposure to PAHs is a multi-dimensional process with a
variety of potential exposure routes. Thus it is inappropriate for monitoring to be
directed to only one aspect of that exposure. When developing a monitoring program
for exposure to PAHs, the program must incorporate both air and some form of
biological monitoring unless statistical analysis of the data indicates that there is a
strong correlation between the personal air and the biological results.
5.6.6 Site Policy
The overall business group has adopted the ALARP policy for any exposures
associated with PAHs. It has also developed a coal tar pitch protocol (Appendix 6) to
which all of the business units must now conform. This is complemented by an audit
protocol against which the sites are regularly reviewed.
5.7
Conclusions
Based on the information derived from this study, it can be concluded that within an
Australian aluminium prebake smelter, workers in the anode plant will have higher
overall exposure to PAHs than workers in the cell-reconstruction areas of the plant.
It is, however, possible that personal air exposure to BSF could be higher in the
reconstruction area depending on the manufacturing process, but the overall body
dose is significantly lower than that of workers from the anode plant.
Within the anode plant, there is further exposure stratification in relation to the
forming and non-forming areas of the plant. Those employed in tasks associated with
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paste mixing and anode forming in the forming area of the anode plant will have
higher exposure to PAHs than those in the non-forming areas; this was demonstrated
in both the air and the biological monitoring results.
Correlation between personal air monitoring for the BSF and 1-OHP in urine of
workers involved with tasks in a prebake smelter was not demonstrated. The
predictive ability of BSF in personal air monitoring in relation to the 1-OHP levels
in urine was very poor overall. It did show some improvement when heterogeneity
and differences across work groups were allowed for, but it was still more modest
than that observed in other studies. This was most likely due to the fact that the bulk
of exposure in the anode plant was as a result of skin exposure and, as a
consequence, BSF in air should not be used as a sole indicator of exposure to PAHs
in the prebake smelter environment. While PPE and smoking presented as
confounders in the overall plant, additional analysis indicated that PPE and smoking
were only significant confounders in the anode plant non-forming area. Work area
location was found to be a significant modifier of the relationship between 1-OHP
levels and BSF.
The use of a definitive BEI in conjunction with 1-OHP in urine would not be
appropriate, as there is too much variability in the ratio of pyrene to BaP and other
carcinogenic PAHs in the different mixtures of PAH. An indicative guidance value
could be determined by utilising the formula proposed by Jongeneelen (1992, 1993)
for coke oven workers and extrapolating for a specific site based on measurements of
ratios of the compounds used at that site. This would be approximate and subject to
change as a result of process or raw material variations.
1-OHP is not an indicator of actual carcinogenic dose, but of the level of a
metabolite of a surrogate marker compound and, as such, is not an accurate measure
of carcinogenic risk. It has been shown to be a better predictor of total exposure to
PAHs than BSF in air as it can take into account multiple routes of exposure.
Consequently, it would be an invaluable tool in the investigation of exposure to
PAHs in many industries.
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van Schooten, F. J., Jongeneelen, F. J., Hillebrand, M. J. X., van Leeuwen, F. E., de
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Kriek, E. (1995). Polycyclic aromatic hydrocarbon-DNA adducts in white
blood cell DNA and 1-hydroxypyrene in the urine from aluminium workers:
Relation with job category and synergistic effect of smoking. Cancer
Epidemiology, Biomarkers & Prevention, 4(1), 69-77.
Viau, C., Carrier, G., Vyskocil, A., & Dodd, C. (1995). Urinary excretion kinetics of
1-hydroxypyrene in volunteers exposed to pyrene by the oral and dermal route.
Science of the Total Environment, 163(1-3), 179-186.
Victorian Workcover Authority. (2000). Code of practice for hazardous substances.
Code of Practice No. 24.
Retrieved April 21, 2006, from
http://workcover.vic.gov.au/wps/wcm/resources/file/ebd8e143a078f6c/COP24
_hazardous_substances.pdf
Weyand, E. H., & Wu, Y. (1994). Genotoxicity of manufactured gas plant (MGP)
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Environment Canada.
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Green Carbon. Comalco Aluminium Limited.
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by high pressure liquid chromatography. Workcover laboratory methods
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Wu, M. T., Mao, I. F., Ho, C. K., Wypij, D., Lu, P. L., Smith, T. J., Chen, M. L., &
Christiani, D. C. (1998). Urinary 1-hydroxypyrene concentrations in coke oven
workers. Occupational & Environmental Medicine, 55(7), 461-467.
Zedeck, M. S. (1980). Polycyclic aromatic hydrocarbons: A review. Journal of
Environmental Pathology & Toxicology, 3(5-6), 537-567.
142
Appendix 1: Participant recruitment presentation
Slide 1
What are PAH’s
• Often formed as a result of combustion
• Exhibit structure of a cluster of benzene rings
• Also known as Coal Tar Pitch Volatiles
(CTPV)
Polycyclic aromatic hydrocarbons
(PAHs) are organic compounds
consisting of 3 or more benzene
rings.
PAHs are not just one compound
but may occur as one of a large
number of different chemical
structures or forms.
They are often formed as a result
of incomplete combustion of coal,
oil, gas forest vegetation or other
organic substances.
The PAH group is also known as
Coal Tar Pitch Volatiles.
Slide 2
Examples of PAH’s
Pyrene
Naphthalene
Anthracene
benz(a)anthracene
benzo(a)pyrene
fluorene
pyrene
Benzo(a)Pyrene
Naphthalene
Slide 3
Occurrence
•
•
•
•
•
•
•
•
There are literally hundreds of
compounds in this group. The
USEPA
lists
16
priority
compounds that are usually tested
for. Some are highlighted here.
Aluminium Smelters
In mineral oils
Asphalt
Coal Tar
Coal (Coking Plants)
Cigarette Smoke
Smoke and Soot
Car Exhaust
PAHs are found throughout the
environment in air, water and soil.
Sources include vehicle exhausts,
asphalt, coal tar, coal and mineral
oils, Smoking kilns for food and
even the Aussie barbecue.
143
Slide 4
Routes of Entry
• Inhalation
• Ingestion
The most common entry of PAHs
into the body is via the inhalation
route when people breathe in air
or smoke containing them.
They may also enter the body
through the digestive system
when food comes from cooking
processes such as broiling,
smoking, roasting and barbecues.
• Skin
In the workplace, they may also
be absorbed via the skin
particularly
where
oils
are
involved. Up to 75% of the total
Pyrene dose can be absorbed
through the skin.
Slide 5
Background
• Historically monitoring has been carried out since
early 1983.
• Always been air monitoring
– Static
– Personal
• Have monitored a number of parameters.
–
–
–
–
Benzene Soluble Fraction
Total PAH
Benzo(A)pyrene
Specific Characterisation of PAH”S
Monitoring of one form or another
has been undertaken at this site
for many years dating back to
1983.
The parameters measured have
varied over the years depending
on knowledge at the time and the
availability of the testing but
generally the Benzene Soluble
Fraction (BSF) has been a
constant. BSFs are a specific
group of compounds that are
soluble in benzene and may be
extracted for analysis. And are
generally
multi-ringed
compounds.
In more recent years air samples
have been fully characterised
breaking down the analysis by
GC-Mass Spectrometry to identify
the many individual components
of the PAH”S.
144
The workplace is monitored on a
regular basis to ensure an
accurate profile of airborne
contaminants is maintained.
Slide 6
Monitoring
• Atmospheric
• Personal
These results shall be assessed
alongside current information in
regard to exposure standards.
• Biological
Both static area monitoring and
personal occupational monitoring
are carried out.
Slide 7
What is the Biological Test for
PAH Exposure?
•
•
•
•
•
Very few tests available
Body absorbs Pyrene in PAH’s
Body converts this to 1-Hydroxypyrene (1-OHP)
(1-OHP) can be found in urine.
This can give some indication of total exposure.
Slide 8
Plant/Process
Static
Monitoring
Person
Personal
Monitoring
Dose
Biologically
Active?
Early Disease
• Blood
• Body Fluids
Tissue
Biomarker
(DNA
Adducts)
• Blood
• Body Fluids
• Imaging
• Tissue Sample
Biological
Monitoring
Biomarker
Levels
Diagnostic Test
Very few tests are available to test
from exposure to PAHs.
The
body metabolises Pyrene to other
chemical substances such as 1hydroxypyrene.
1-hydroxypyrene can be found in
urine of individuals exposed to
PAHs.
By measuring the level of 1hydroxypyrene in urine at the
beginning and at the end of a shift
rotation it is possible to get some
indication of a person’s exposure
in the last 6–30 hours. This will
account for inhaled, ingested and
any absorbed through the skin.
It is not possible these tests to
predict resultant health effects.
There is a multistage approach to
the monitoring of PAHs in this
project.
The first of the stages involves
static environmental monitoring
and looks predominantly at the
plant and the controls associated
with the process.
The second stage involves
personal monitoring and gives
some indication of the potential
exposure levels of the individual.
The third phase looks at the
actual dose that has been
absorbed by an individual and is
the first stage of the biological
monitoring.
The fourth stage investigates the
potential effect of the absorbed
dose and the formation of DNA
145
adducts. These are indicators of
damage occurring to the DNA
which the body is continually
repairing.
The fifth and final stage is the
diagnosis of early disease which
would involve a range of medical
diagnostic tools.
This project will concentrate
mostly on stages one, two and
three.
Slide 9
Health & Exposure Monitoring
•Preliminary monitoring has shown intermittently high
exposures in some specific tasks.
•To see if these exposures are biologically significant we
are going to carry out a staged biological and air study.
•This study will look at levels of PAHs in the air as well as
looking at a marker compound in the urine.
Slide 10
Sampling Requirements
• Environmental
– Static & Personal monitoring using personal
pumps (current routine procedure)
• Biological
– Pre shift & post shift urine sample. (current
routine procedure)
Early years have concentrated on
environmental measures and
more recently we have started
looking into biological monitoring
to assist us in determining the
level of contaminant absorbed into
the body system.
We would like to undertake a
study which will look at the two
methods air and biological and
carry out some comparisons to
identify how they correlate and
possibly which is the more
applicable method for our site.
The sampling protocols for the
environmental monitoring using
personal pumps and the urine
sampling for 1-hydroxypyrene will
not vary from the methods and
procedure which are currently in
place for the site routine
monitoring.
.
146
Slide 11
Sampling Questionaire
• Prior to providing a urine sample, each participant is
required to complete a self-administered questionnaire.
The questions are aimed at determining such aspects as:
• General demographics, ie, age, sex;
• Possible exposures in the previous 48 hours, both
occupational and non-occupational;
• Smoking habits;
• Potential food source of PAHs; and
• Personal protective equipment worn.
Slide 12
1-OHP Sampling Pack
Prior to the sampling process we
would like you to fill out the
sample sheet questionnaire and
to sign the authorisation form on
the back. It should only take a
couple of minutes but the info is
very important to us. The
questions are pretty straight
forward and we will run through
them with you on the day just in
case you have any questions.
The sample pack will contain
Biological sampling sheet &
questionnaire
Work Log sheet
Four sample containers, two for
pre and two for post shift samples
Two Biological hazard bags
Two plain brown paper bags.
You will be required to provide
two samples before the start of
your first shift of the rotation and
two last thing on the completion of
your final shift. The samples need
to be left in the small freezer in
the back of the main lab (just
follow the signs at the lab) The
biological sample sheet and
SIGNED
authorisation
sheet
should be placed in the back
compartment of the bio-hazard
bag NOT the same compartment
as the sample.
Don’t worry if you can’t remember
this as we will be going through
this again with you when we give
you your sample pack.
147
Slide 13
Results
• All results will be reported generically on a group
basis at team meetings as per past report back
sessions with the option of a one on one session on
request.
• There will be no individual identification of
results.
• All individuals will be asked to sign an
authorisation form.
• As this is part of a Queensland University of
Technology study, Ethical approval has been
sought from the university ethics committee and
granted.
All results will be reported back to
the group as a general report with
no individuals names attached.
You will have access to your own
personal results and can discuss
them with either myself or the
doctor at our medical centre. All
results are strictly confidential and
will be kept under lock and key in
the medical centre or on a
secured drive on the computer
network.
As mentioned before it is not
compulsory to participate but it
would be greatly appreciated. If
you do participate in the study you
will be required to sign an
authorisation form.
The study has QUT ethics
committee approval and is
available for anyone to look at on
request.
148
Appendix 2: Participant consent form
Consent Form
Chief Investigator:
Ross Di Corleto
Boyne Smelters Limited
Occupational Health & Hygiene
Phone
4973 0319
Project Title: Biological Effect Monitoring of Occupational Exposure to PAHs in
Pre-Bake Smelting
The investigator conducting this research project abides by the principles governing
the ethical conduct of research and at all times, avows to protect the interests,
comfort and safety of all subjects.
This form and the accompanying Subject Information Package have been given to
you for your safety and information. They contain an outline of the experimental
procedures and possible risks.
Your signature below will indicate:
1. You have received the Subject Information Package and that you
understand its contents.
2. You clearly understand the procedures and possible risks involved; and that
you have been given the opportunity to discuss the contents of the Subject
Information Package with one of the investigators from Boyne Smelters prior
to the commencement of the experiment.
3. You understand that all the data, which you have provided, will only be
revealed to the investigators and yourself. When the results of the study are
published you will remain anonymous
4. Your participation is voluntary and therefore may be terminated at any
moment by you without comment or penalty, and without jeopardising your
involvement with the Boyne Island Smelter.
5. You may direct any enquiries and further questions to the Chief Investigator
of this project, Ross Di Corleto on ext 2319 or Comalco Principal Medical
Adviser Dr Gerry Walpole on 3867 1658. You may also direct complaints
and concerns regarding the ethical conduct of this investigation to
Queensland University of Technology, Secretary, University Human
Research Ethics Committee (Ph no 3864 2902).
6. You will receive feedback on your results at the time of the Study, and
149
7. You agree to participate in the experimental procedures set out in the
Subject Information Package for the research thesis entitled “Biological
Effect Monitoring of Occupational Exposure to Polycyclic Aromatic
Hydrocarbons in Pre-Bake Smelting.”
Your Details:
Name ……………………………………
Phone ………………………………
Address …………………………………………………………………………………
…………………………………………………………………………………………..
To be signed in the presence of a witness:
Signature …………………………………….. Date ……/……./………
To be signed by the person witnessing your signature:
Witness Name: ………………………………………
Signature …………………………………….. Date ……/……./………
To be signed by the researcher:
Ross Di Corleto
Signature …………………………………….. Date ……/……./………
To date site routine monitoring has been undertaken to attempt to identify the level
of exposure of individuals to Poly Aromatic Hydrocarbons (PAH). This has included
personal air monitoring and biological monitoring i.e. analysis of urine for a
compound called 1-hydroxypyrene. This monitoring will continue as part of a study
into the effectiveness of the monitoring and the review of Biological Exposure Index
guidelines.
•
Each participant is requested to provide 2 X 50 ml of urine, at the beginning
and end of the shift rotation, which will be placed in the laboratory sample
freezer in the containers provided. The researcher will transfer this to the
BSL Medical Centre sample freezer. Queensland Medical Laboratory Staff
will then collect it for transport to NSW Workcover Laboratories for analysis.
•
Each participant will be given information on the project and details of the
collection time via a presentation or personal interview.
•
Urine samples will only be tested for 1-hydroxypyrene. No other testing will
be undertaken without the permission of the participant.
•
All individual results will remain confidential.
150
Appendix 3: Participant daily work log
151
Appendix 4: Participant questionnaire
1-HYDROXYPYRENE BIOLOGICAL SAMPLE SHEET
Urine sample code: (office use only)
Name
Classification
Date of Birth
___/___/___
Ë Male
Ë Female
Job/Task
MRU/Section
Date and time of sampling
Pre-shift
Time
___/___/___
Date and time of sampling
Post-Shift
Time
___/___/___
Smoking (cigarettes/cigars/pipe):
Yes Specify:
if yes, average number per day:
Use of coal tar products in the last 7 days.
No
Yes Specify:
(eg.: coal tar ointment/shampoo, etc.)
No
PAH exposure at home in the last 7 Yes Specify:
days:
No
(eg.: timber treatment with creosote, bar-bque, burning off)
Personal Protective Equipment
Yes Specify:
i.e. Respirator, disposable overalls,
No
Describe conditions of exposure during the two work shifts preceding sample collection with an emphasis
on skin contact and personal hygiene. (ie. high exposure cleaning ductwork previous shifts, low exposure
in control room.)
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Skin Exposure Classification (Check one):
Level 1: Minimal to no opportunity noted for visible contamination of skin or clothing with CTP, or carbon material known to contain CTP.
Level 2: Periodic opportunities for visible contamination of skin or clothing.
Level 3: Regular or routine visible contamination of skin or clothing.
Comments:
________________________________________________________________________________
__________________________________________________________________________
Sampled By: _________________________
152
Appendix 5: Statistical analysis roadmap
All the data groups were sorted and four transform approaches applied:
o Data was squared
o Square root of data was taken
o Natural Log
o Logarithm to the base 10
Each of these groups of data were then analysed using the Anderson-Darling
normality test and examined using six questions addressing basic criteria associated
with normal distributions. Basic statistical calculations were also performed such as
mean, median standard deviation, variance, skewness, kurtosis and confidence
intervals for the mean & median. The six questions were:
1. Is the mean of the data set within 10% of the median?
2. Is the standard deviation ≤ 1/2 of the mean?
3. The minimum & maximum range of the mean should fall within ± 3 standard
deviations.
4. Skewness –3 to +3?
5.
Is the kurtosis, within –3 to +3?
6. Does the distribution have the characteristic bell shape?
153
Appendix 6
Aluminium Smelting Protocol for Coal Tar Pitch Volatile (CTPV) Risk
Management
Code of Practice Objective
The Company shall reduce exposure of employees and contractors to CTPV and
associated PAH to as low as is reasonably practicable.
Program of Work
1. The Company guidelines for CTPV/PAH are:
•
BSM/CSM air monitoring is < 0.1 mg/ m3 per 12 hour shift
•
End of shift urinary 1-OH-pyrene of < 4.9 µmol/mol of creatinine1
•
Benzo (a) pyrene in air monitoring is < 0.2 µg/m3 per 12 hour shift
2. Personnel exposed to CTP products will be monitored. Examples may include:
•
Green Carbon operations and maintenance personnel
•
Liquid pitch transport and storage
•
Cell reconstruction
•
Cell bake outs
3. An accredited provider with approved protocols for analysis of CTPV and
associated PAHs shall be used.
4. All results will be notified to the individual and the accountable leader. Results
that are greater than 3 times the 1-OH-pyrene guideline or unexpected exposures
greater than three times the CSM/BSM and B(a)P OEL will be investigated and
feedback given.
The investigation of 1-OH-pyrene results will have two components:
•
Inquiry into workplace practices and procedures during the time of exposure
led by the accountable leader (a record of the work activities undertaken
during the exposure period will be reviewed as part of this investigation.
1
Jongeneelen, F. J., “Benchmark Guideline for Urinary 1-Hydroxypyrene as Biomarker of
Occupational Exposure to Polycyclic Aromatic Hydrocarbons”. Ann. Occ. Hyg., Vol 45,No1 pp 3-13.
154
•
A health consultation will be held at the site medical centre to discuss the
health significance of the results, if any, and initiate any follow up actions
necessary.
The monitoring results, investigation outcomes and a presentation explaining the
significance of these will be made available to the relevant on-site
personnel/teams. Individuals will receive their own results with an explanation as
to their significance.
5. Pitch burn shall be reported and where necessary, treated at the medical centres
and recorded as first aid treatment cases.
6. Water-based barrier creams do not increase CTPV absorption through the skin
and may be used as added protection against CTPV skin exposure and prevention
of pitch burn.
7. Appropriate annual medical surveillance will be carried out on individuals in
exposure groups where the 95th percentile for
•
BSM/CSM air monitoring is > 0.1mg/ m3, or
•
Urinary 1-OH-pyrene levels are > 4.9 µmol/mol of creatinine, and/or
•
Benzo (a) pyrene in air monitoring is > 0.2 µg/m3.
10 The common hierarchy of control will be deployed at all sites depending on the
results of the exposure data. The hierarchy of control are
Controls that prevent exposure
• Elimination
• Substitution
• Isolation of the people from the hazard or the hazard from the people
• Implementation of engineering controls
Controls that mitigate exposure
• Implementation of administrative controls such as changes in work practice.
(Note increasing the number of persons exposed to reduce individual exposure
155
is not an acceptable administrative control when dealing with potentially
carcinogenic substances.)
• Use of PPE as an interim measure while higher control strategies are being
implemented
Controls that prevent exposure eliminate illnesses and are always the preferred
option.
Employees working with CTP will be adequately informed, instructed, trained
and supervised to reduce exposure to CTP to as low as reasonably practicable.
The mandatory education/training package used across the Company at
commencement of exposure and annually thereafter shall include:
•
Definition of CTPV/PAH, exposure pathways and affects of exposure.
•
Potential health issues including skin, bladder and lung cancer.
•
Relevant exposure standards and specific hygiene measurements
appropriate to the exposure group.
•
Respiratory protection requirements including types of respirator
appropriate for the level of exposure, respirator cleaning practices and
filter change requirements. There shall be a requirement to wear
appropriate respiratory protection in all areas or tasks where the
workplace exposure to CTP has been shown to exceed
0.05mg/ m3 BSM in air.
•
Use of skin cleansing, barrier creams, clothing and gloves.
•
Encouraged use of showers /sauna / personal hygiene /sunscreen.
•
Potential reproductive effects.
11. Quantitative fit testing of respirators will be performed prior to issue, with repeat
testing at a maximum one-year interval. Respirator maintenance education will
be repeated at each fit testing. Documented respirator maintenance programs
will be put in place.
12. Laundered work and/or disposable clothes will be provided on a daily basis to
designated exposure groups for the purpose of reducing skin absorption. These
exposure groups will be required to shower prior to leaving the site and after any
significant exposure. Under no circumstances shall any clothes, belongings or
156
PPE that are contaminated with CTP be allowed to leave sites except if taken for
laundering by approved laundry contractors.
13. No eating drinking or smoking shall be allowed in production or other designated
areas where CTP is processed eg in Green Carbon or where dust and/or volatiles
are emitted eg in Potrooms during cell bake out. Separate washing facilities shall
be provided so that exposed groups can adequately wash prior to eating or
smoking in designated areas.
14. Change house facilities shall be arranged such that the potential for cross
contamination of clean and dirty clothing and articles is minimised. Clean and
contaminated clothing or articles shall under no circumstances be stored together.
15. All smelting sites shall identify and share information regarding improvements in
exposure reduction through alterations in processing and plant. All smelting sites
shall identify and share information regarding workplace monitoring and health
surveillance improvements and knowledge.
Auditing Guidelines
The corporate occupational health and hygiene specialists in conjunction with the
Carbon leadership team shall review the progress of application of this protocol on a
yearly basis. The audit would involve
•
Visit each site
•
Review occupational hygiene data and improvement projects
•
Make recommendations to relevant site managers for further work required to
support the intent of the protocol
•
Sites will undertake six monthly risk assessments and reviews
157
Appendix A. Medical Surveillance Protocol
Definitions
Exposure Criteria
Medical surveillance will be carried out on individuals in exposure
groups where the 95th percentile for
•
•
•
•
BSM air monitoring is > 0.1mg/ m3, or
Urinary 1-OH-pyrene levels are > 4.9 µmol/mol of
creatinine, and/or
Benzo(a)pyrene in air monitoring is > 0.2 µg/m3
There is potential for direct skin exposure to CTPV more
than twelve times per year
Employees/Contractors will become eligible to enter the
surveillance programme after three months in the role. Equivalent
exposures at other sites will qualify for entry into the surveillance
programme.
Medical Surveillance Criteria
Mandatory medical surveillance will commence 7 years from the
time of first working with pitch. Eligible employees/contractors
may choose to initiate medical surveillance one year after exposure
begins
Site Medical Adviser
Means a medical practitioner who is either a specialist in
occupational
medicine, OR who has satisfactorily completed a health
surveillance training program supplied by the Division of
Workplace Health and Safety of the relevant state, territory or local
equivalent.
Objectives
•
•
Standards
To have an effective and confidential medical surveillance
program for the early identification of pitch related disease.
To improve control measures for the Company employees and
contractors who are exposed to pitch, through the identification
of disease patterns and the underlying causative factors.
All the Company employees and contractors who meet the
exposure and health screening criteria for pitch will undergo
annual health assessments These health assessments will begin
7 years from the date of first exposure to pitch at the Company
or other work places.
• The health screening will be undertaken with supervision and
direction from a Site Medical Adviser.
• Health screening will meet the standards outlined in
‘Workplace Health Surveillance’ (1993) - Australasian Faculty
of Occupational Medicine.:
•
158
•
•
•
NOHSC “Competencies for Health Surveillance June 1998
To arrange appropriate medical referral for the Company
employees or contractors who are identified by the health
screening program as having possible pitch related disease
The requirements of the ‘Hazardous Substances Compliance
Act’ - 1995 will be met.
Accountabilities Manager accountable for Occ Health
The Manager accountable for Occ Health will be accountable for the management of the health screening program
for pitch at the Company sites.
Department Managers
The Department Managers will • identify all the Company employees who currently work, or who
have worked, in the department, and meet the exposure criteria.
• ensure that all the Company employees and contractors who meet
the screening criteria undergo health screening.
Superintendents
The Superintendents will • ensure that all crew members who meet the exposure and
screening criteria undergo health screening, and to assist their
team members if they have issues with the health screening
program.
Manager accountable for site contractors
The Manager accountable for site contractors will •
advise the Site Medical Adviser of all the Company contractors
who meet the exposure and screening criteria.
The Company employees and contractors
Employees and contractors will • undergo appropriate health screening for pitch related diseases
• ensure that they understand the results of their health screening
Site Medical Adviser
The Site Medical Adviser will• design and maintain an up to date health screening program,
taking into account each employee’s or contractor’s level of
exposure to pitch.
• ensure that such screening is undertaken to a high level of
professional and ethical standards.
• ensure that the results of the screening, and their significance, are
explained to each person in a way that is understood by them.
• arrange appropriate referral for further medical assessment if this
is indicated by the results of the health screening.
• maintain normal medical confidentiality of each person’s health
screening results and records.
159
•
provide a report with statistical data, in a format that does not
identify individual employees or contractors, to the Manager
accountable for OHH to help identify any disease patterns and
possible contributing factors
Occupational Health Nurses
The Occupational Health Nurses will• perform health screening to high professional standards.
• explain procedures to each person in a manner that is understood
by the company employee or contractor
• maintain medical confidentiality of each person’s health screening
results and records.
References
Hazardous Substances Compliance Code -(1995)
Workplace Health Surveillance- AFOM (1993)
Appendices A & B
The health surveillance program consists of the following elements:
•
•
•
•
Occupational history and qualitative estimation of exposures to pitch.
Occupational and medical history.
Physical examination.
Urinalysis.
160
Pitch Health Assessment
Surname: ______________________
DOB: ____/___/_______
Given Names: ____________________________
Gender: __________
Department: _______________
Smoking history, exposure to sunlight/previous sunburn, usage of sunscreens and
barrier creams, previous history of pitch burn?
History
1) Have you been exposed to pitch at workplaces other than this site?
YES
NO
If YES, please outline details_____________________________________________________________________________
_____________________________________________________________________________
Years
Company
Job
2) How often were you exposed to pitch?
Every Day
Weekly (>2/7)
3) What is your present exposure to pitch?
Every Day
Weekly (>2/7)
Monthly (>7/7 x 12)
Rarely
Monthly (>7/7 x 12)
4) Have you noticed any skin changes since your last medical?
Rashes:
Yes
No
Moles/sunspots:
Yes
No
Rarely
Burns:
Yes
No
5) Describe any other symptoms that you think may be related to your exposure to pitch.
Comments:
____________________________________________________________________________
_____________________________________________________________________________
6) When passing urine have you noticed:
Blood:
Burning:
Yes
No
Yes
No
Frequency:
Yes
No
Pain:
Yes
No
Difficulty:
Yes
No
Comments:___________________________________________________________________
______________________________________________________________________
Biometry
Medical Examination
Height: ________________________
Weight: ________________________
Urinalysis:
Alb ____ Blood _____ Glucose _____
Nose: __________________________
Skin:- Head/neck _________________
Legs:
_____________________
Trunk:
____________________
Chest:
____________________
Arms:
____________________
Abdomen:
_________________
Scalp:
__________________
Other:
__________________
Skin type? SPT I - VI
SSMA comments:
_______________________________________________________________________
_______________________________________________________________________
SSMA Signature: ___________________________
Date of next review: ________________________
Date: _____________________
161
Appendix 7 Green Carbon PPE Matrix
162