1. No category

DISCUSSION OF THE
Asbestos bulk sample analysis
quality assurance programs
There is no way to be certain of the
identity of all' of thesefibroucs materials
unless the probl'emis approached scientifically andvtaith proper training in the
characterization of f hers by all of the
parameters that can be rneasured with
tlie polarized light rnicroscmpe ..
Ti-ts a:NAt.YriCAt; Ptzoat.Fms involved! in properly
identifying asbestos and asbestos substitutes in, bulk
insulation are documented in Reference 1 . Harvey
evaluated 35,000 0 analytical results submitted' to Research Triangle Institute (Research Triangle Park,, North
Carolina) under the : United States Environmental Pro tection . Agency's (U .S . EPA), Asbestos Bulk Sample
Analiysis QualityAssurance Program and!the UIS . Navy
Asbestos Identification Proficiency 'I'esting, Program .
False positive : results, that is, reporting asbestos when
none ! is present, are usually due to confusing shredded
pol'yethylene,, nemalite (fibrous brucite), wollastonite,
or talc : fibers with chrysotile . False negatives are more
often associated with low percentages of asbestos . There
are also identification errors, especially between anthophyllite and tremolite, chrysotile and shredded'
polyethylene, and between wollastoniite and'actinolite,
By WNalter C'. IW1cGrone
Df:MeCtrorte is Director, McCrone Research Institute, Chicago,
Illinois, U:S.A . The Irrstitute teaches a varietyaf one-week intensive
courses in the application of microscopy to industrial research', con
tamination control, criminalistics, etc ., nearly 150 times eachl year
in different' cities in the United! States and' other countries : Dr.
McCrone is Editor and,Publistier of The Microscope, an applied'
quarterly jpurnal of microscopy.
This article is adapted from one which appeared in The Microscope
37 47-56 (1989).
16 : 4/90 1
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Discussion
The morphological and, especially,,the optical!properties of all l of these substances are distinctive and form
the basis for certain identification for anyone proficient
with the pol'arized light!microscope and d'ispersion staining (DS) . It is not strictiy neeessary to use DS because
it is based on refractive index and this can be determined
by the usual Becke line methods . The rapidlidentification of small! particles by DS is faster and easier .
There is no way to be certain of'the identity of'all
of these fibrous materials unless the problem is approached scientifically and with proper training in thee
characterization, of fibers by all I of the parameters that'
can be measured! with the polarized light microscope .
These incltrde shape, size, color, refractive indices, DS
colors (both parallel (11) land perpendicular (1)' to thee
fiber, length), pleochroism, birefringence, extinctronn
angles, and signs of elongatiom Unfortunately, many
analysts working on bulk samples lack a scientific attittidb andVor a scientific background . A few years ago,
there were far fewer analysts and most of'them, had'~
taken mineralogy courses including opticali crystallography . With that background~ one would! expect very
little difficulty in identifying asbestos when it is present
and not finding, it! when it is absent. M'ore recently,
with the tremendous number of' samples that must be
analyzed, many additional analysts have been ipressed
into service . Few of them, are mineralogists, some have
little or no chemical background ; and some have no
science background . These people can be expected to
have considerable difficulty unless they develop the
proper scientific approach and have : access to proper
training .
It should be noted that the samples selected for these
quality assurance programs are somewhat skewed toward more : unusual' problem compositions . Few ana+
lysts, even those with little microscopical training, have
trouble identifying, chrysotile when it is present in a :
reasonable percentage . Most samples in, the rreal' world
contain ~chrysotile with amosite as a close second : Prob1em samples are very much in, the minority andl they
are the ones that (very properly) have been emphasized
by the U .S . EPA program . . Presumably, errors on the
easier real-world samples should be less frequent! than ~
the results Harvey reported for the U .S . EPA and Navy
programs . This may be some consolation but it is stilll
not a proper situation to have analysts able to do all of
the easy samples, but who fail lwhenever the occasional
unusual sample comes along . In spite of this, I believe
the pereentage of false negatives and especially false
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QUALITY ASSURANCE continuedd
positives in the real world is even greater than the reported UIS . EPA and Navy result's : Those who work
the U .S . EPA and' Navy samples are most likely on
their best behavior and under pressure to be right . In
the real world, where some analysts are trying toaanalyze :
50 to 100 bulk samples per day, ,the results are far worse .
The major problemis obviousiy the difficult detection
of shredded polyethylene fibers and theirresulting ;id'entiification as chrysotile. There is no excuse for thatierror
based! on the optical'. properties (and as polyethylene
melts with a match) but the number, of real world sampl'es one can expect to encounter containing polyethylene are few and far between . Most analysts will never
see such ~a sample . Shredded'.polyethylene ; though common today ini ceiling sprays, has only been available
during the last few years and! iis found in almost none
of the buildings that have : fiber-containing insulation.
The following, describes the specific procedures for
reliable detection of each of the problem fibers : chrysotile, polyethylene, talc,,brucite, tremol'ite„anthophyllite, actinolite, wollastionite, amosite, and crocidolite :
Chrysotile
Any fibers, whether straight or meandering, with,
widely varying,diameters from broad bundles down to .
18 ; e, 4l90'
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the resolving,power limit of the light microscope„with
matchimg, wavelength (Xa) colors in 1 .55 Cargillle highdispersion (HD) liquid of magenta (11) and blue (1) or
with Ao close to those values, and a difference in ko
values of about 100 nm, are almost undbubtedly
chrysotile . The only conceivable look-alikes that come
close to these properties are animal hairs, spider webs,
leather, and shredded!polyethyl'ene . These would all be
eliminated by a flame test; ehrysotiile wouldl not change
optically in a quick exposure to any temperature below
5()D°'F, whereas polyethylene melts at 1L35°C or less .
Polyethylene
In shredded'' form, polyethylene shows a, variety of
diameters and morphology nou distinctively different
from chrysotile . Idowever,, it shows DS colors of yellbw
(11) and blue (1) with a difference in ko of about .200'.
nm . Its birefringence is nearly three times greater than
chrysotile. The unknown thickness of particular fibers
makes it difficult to use this parameter however . The
difference iniao values shouldl alerrthe carefully trained
analyst to the possibility that s/he has polyethylene . .
Then, holding the 1 .55' HID preparation over an alcohol I
~
lamp, cigarette lighroer, or match„ or placing it on ai
hotplate at about 160QC for about 30, sec will melt
C
polyethylene fibers .
dV
Talc
Another chrysotile look-alike is talc . Talc fibers are
thin ribbons, some of which may resemble chrysotile
in shape ; however a study of knowns shows that they
are usually straighter . When not straight, the fibers
usually bend abruptly between straight segments . Talc
fibers have two much higher refractive indices in the
plane of the ribbon that are much higher than any indexx
of chrysotile and therefore, show a pale yellow color
lengthwise in 1 .55' HD liquid, very different from any
of the chrysotile 7ia colors . The confirmation of' talce
fibers would be that one of the two differentcrosswi'set orientations shows two different h, colors
; chrysotile
shows the same color in allicrosswise orientations . Talcc
shows a pale yellow in the crosswise direction, if thee
ribbon is lying, flat, and blue if the ribbon is on edge .
Slh'ght pressure on the coverslip with a gentle up-an&down motion of the needle exerting the pressure, shows,
any talc fiber oriented crosswise of the vibration, direction of the polars changing in ko colors fromi yellow too
blue :
Btucite (nemalite) 1
Nemalite, the fibrous form, of the mineral brucite,
has a definite asbestiform shape, although usually
straight and stiff (imore like the amphiboles) . It is positively identified as nemalite by its refractive indices .
All three indices are higher than chrysotile and the k ;p
colors in 1 .550 HD are pale yellow to yellow . Most
distinctive is that the palest yellows are crosswise of
the length, hence, nemalite fibers have a1 negative sign
of elongation . However, it should be noted that, if
heated, nemalite then shows a positive sign of elongation although the indices change only slightly . Both Ao
colors of yellow to pale yellow in the 1 .55 HD liqµid
or only pale blues in the 1 .605 ~ Hm liquid should still
identify this chrysotile look-alike no matter which sign
of elongation is observed . HeatedInemalite also assumes
a yellow absorption color and becomes more brittle
with respect to crosswise fracture .
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TremolFte
Tremolite fibers are usually straigYst! andl stiff and
closer to a blocky, shape than amosite, or especially
chrysotile . Its refractive indices are very close to 1 .605
HD:One obtains threedifferentJte colors, yellow nearly
parallel to the length and magenta or bliue perpendicular
to the length, Again, a given fiber of tnemolite, free to
move in the 1 .605 HD, liiquid, can show either bllue or
magenta crosswise Xa colors with slight up and down
movement of the coverslip with a needle . At this point,
however, the fibers eould be tremolite or anthophyllite .
A positive way of d'ifferentiating, tremolite from an+
thophyllite is the presence of oblique extinction for
tremolite and i parallel eztinction, for anthophyllite . The
extinction angles for tremolite vary from 0-20°'depending on the position of rotation about, its length . Ran-
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QUALITY ASSURANCE continued
domly oriented~ nonfibrous crystals will show any anglee
between 0'-20°; however, most of them will show at't
least a small oblique extinctiion angle and some may,
exceed 10q . Fibrous tremolite shows lower extinctioni
angles, usually from 0° to about 4° .
Anthophyllite
Anthophyllite is a tremolite look-alike with the added I
problem that' its refractive indices are very similar . One,
would expect to obtain very similar Xa, colors, again,
with yellow parallel to the length and blue or magenta
crosswise . However, anthophyllite is differentiatedd
from t'remol'ite by its lack of oblique extinction . All
orientations of randomly oriented' anthophyllite fibers
willl show 0° extinction angles . I'n practice„ one ex amines a number of different fibers showing blue,
magenta, and yellow DS colors in 11 .605 HDD for extinc tion angles, If alll show parallel extinction, the fibers
are anthophyllite ; if most show oblique extinction they
are tremolite .
The determination, of extinction angles requires thatt
the polar vibration, directions coincide with the crosslines . This does not happen automatically . It must be
set and confirmed by the analyst. If they are not coincident, then an oblique extrnction i angle may be observed, and mistakenly reported . If, however, alll of the
crystals observedlshow the same, say, 3°obl'iqueextinction on either side of the crossline, it means that the
extinction is parallel and that the polars are misalignedl
relative to the crosslines by 3° :
Actinolite .
Actinol'ite is a higher refractive index member of the
tremolite series and, as such; shows yellow to pale
yellow DS colors in the 1 . 605 HD liquid. The morphol,
ogy of actinolite is similar to tremolite and both show
similar extinction behavior (0-20P when nonfibrous and
0-49 when fibrous) . It is notnecessaryto remountactinolite in 1 .630 HD liquid ini which it shows DS colors
close to those of tremolite in 1 .605 HD . Allthoughlit is
not necessary to remount the sample, it is necessary,
in the 11 .605 HD liquid, to see only yellow ko, colbrs
in all orientations to differentiate it from tremolite and'
to check the sign, of elongation on a dozen or more
particles . If a positive sign of'elongation is determined
on alll particles, the fibers are actinolite and not wollastonite which also has yellow DS colors in 1' .605 HD . .
The actUali refractive indices for actinolite or any of
the asbestos mineral'fibers can, be determined from dispersion staining data using the procedure published by
the author.2
liquid . Its chief andi very important distinctive feature
is the fact that its intermediate (3 refractive index lies
(more or less) parallel to the length, whereas actinolite
has its highest refractive index (more or less), parallel
to the length Actinolite, therefore, always has a positive
sign of elongation but wollastonite may be either posi~tive or negative . If a large number of fibers are presentt
in 1 the sample, then examination with a red' I-plate and
crossed polars will show a positive sign of elongationn
for most wollastonite fibers but perhaps one ini five willl
show a negative sign of elongation . This is a corroboration for wollastonite . Gentle pressure on the coverslip
with a needle usually rotates most wollastonite fibers
from a positive to a negative sign of'elongation, .
Amosite
Amosite has the highest refractive indices of any of
the colodess asbestos-types . It is made up of long,
straightl, stiff fibers with highly variable diameters and
X. colors in 1 .6801HD liquidlof'bllue (1) and gold (11) .
Its sign of'elongation is positive and its extinction i is
parallell or oblique but because of lamellar twinning,
the maxiimum, oblique extinctioniangle is only 4" or 5°,
altlioughi some very fine fibers show higher angles.
If'heated (as in boiler insul'atlon), amosite changess
in refractive index and color . It develops a yellow to
red color with pleochroism ;,the strongest absorption is
parallel to the length . Rotation of the stage shows it
then to be pleochroiic . Accompanying the color change
is a corresponding change in refractive index ; the redder
the fiber, the higher the refractive index . We have observedlindices in excess of'1 .90 flj) andI 1 .80 (1) .
Crocidolite .
Crocidolite (blue asbestos), is easily identified' by its
shape, highly variable diameters, blue colbr, and pleochroism with deep blue (11)'and!gcay blue (1l) . Its refractive indices are higher than those of amosite and the ko
colors for all orientations are yellow in 1 .680 HD liquid .
The palest yellow is perpendill to the length indicating a negative sign of elongation ;,this is confumed' with
the red 1-plate .
Concluslon,
Anyone confidentim their understanding of these tests
and able to carry out and! interpret the results of such
tests, should have no problem in id'entifying,anyof the
above materials . Anyone unable to do so has either not
had proper training or has not taken full advantage of
that training .
1+W ~~ollastoroite
References
Wollastonite is another asbestos llaok-alike and by
shape alone, cannot be differentiated from, any of the
asbestos minerals (except~ chrysotile) . Wollastonite has
refractive indices very similar to actinolite and, therefore, shows yellow to pale yellbw ini the 11 .605 HD'
20, :
1 . HARVEY ., B
., ~"ClassitiCationlandidentification eliortendenCiesinbulk insulation proficiency testing matCrialS,"M'icroscope373891
398 (1989) ;,A'm . Env . Lab ;,2(1) 8-14(I990) .
2. t.accRONE ; w ., "Detennining,refractive indices from dispersion
staining data ; " Microscope 37 47-56 (1989) .
4190
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