How to measure formaldehyde exposure Roberge Brigitte, Occupational hygienist, ROH, Buissonnet Sophie, Gravel Rodrigue and Goyer Nicole, CIH Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST) CONTEXT OF STUDY In the context of a study to estimate the health and economic impacts of lowering the current threshold limit value (TLV) ceiling of 2 ppm for formaldehyde to a TLV ceiling or time-weighted average (TWA) of 1, 0.75 or 0.3 ppm, the current exposure of Québec workers was evaluated in many economic activity sectors. Knowing the reliability and limits of the measuring methods was then of primary importance, particularly for the real time measurement. Clic Research www.irsst.qc.ca Two methods were used in parallel for TWA exposure: Parameter Collection medium Sampling Analytical method Detection limit METHOD NO1 Photo pump XAD-2 polymer tubes impregnated with hydroxymethyl piperidine 1-6 hours 0.2-0.3L/min Gas chromatography with NP detection 2 µg LINEAR REGRESSION [Badge] = 1.02 [tube] – 0.03 [Badge] = 0.72 [tube] + 0.07 METHOD NO2 Photo badge Badge impregnated with 2,4-dinitrophenylhydrazine 1-6 h Passive diffusion (0.0286 L/min) High pressure liquid chromatography with UV detection 0.21 µg CORRELATION COEFFICIENT R2 0.99 0.89 NUMBER OF DATA 56 137 RESULTS Response curve : INNOVA Photo Innova 12% 0.15 ppm Accuracy Precision INSTRUMENT NO1 INSTRUMENT NO2 INSTRUMENT NO3 CMS Colorimetric reaction read by an optical sensor (CMS) 100-600 sec (depending on concentration) PPM Electrochemical cell analyzer Response time Innova Infrared analyzer with photoacoustic detector (IN) 60 sec 10 sec (needs a decontamination period between two readings) CONCENTRATION READ BY INSTRUMENT #1 > 1.5 PPM > 1.0 PPM < 1.0 PPM < 0.5 PPM LINEAR REGRESSION Photo Innova [CMS] = 0.87 [IN] – 0.35 [CMS] = 0.76 [IN] – 0.01 [CMS] = 0.53 [IN] + 0.24 [CMS] = 0.46 [IN] + 0.22 CORRELATION COEFFICIENT R2 NUMBER OF DATA Criterion: 0.43 0.37 0.11 0.03 57 85 91 29 Three instruments were used in parallel for ceiling exposure, in ambient air during the last 30 minutes per station Parameter Detection principle ● ● ● ● ● For instrument no3, because of decontamination period (up to 30 minutes), and the build-up of baseline, we stopped its use after a few tests. No good correlation was found between the instrument #1 (IN) and instrument #2 (CMS) readings. In most cases, the CMS readings were less than IN: interference of chemicals and effect of temperature and humidity on CMS partly explain this fact. Ceiling exposure evaluation is still a problem in cases where other chemicals are present. The presence of other chemicals was suspected of affecting the readings. Concentration Collection medium Analysis FORMALDEHYDE (HCHO)P Air stream at the top of the heated paraformaldehyde at 80 °C 0-2.5 ppm (for response curves) 0.6-1.4 ppm (for interference) XAD-2 Gas chromatography with NPD PPM - 30% 0.11 ppm 50% 0.31 ppm 21% 0.11 ppm INNOVA MIRAN CMS PPM 0.23 2.18 22.7 555 295.4 489 0.85 2.92 35.2 98.1 -0.76 1.44 -0.63 -1.97 8.4 9.0 0.20 1.66 3.08 6.13 <0.2 0.9 <0.2 1.7 <0.2 1.7 <0.2 3.2 <0.2 3.1 8.84 5.2 0.9 2.6 6.5 7.1 0.1 1.0 <0.1 0.8 ● Effect: Reading > 2 x limit of quantification ● Interference: Reading – analytical result HCHO > 2 x limit of quantification Substance Naphtha VM&P Ethylbenzene Butanol Xylenes Toluene Ethanol Methanol Phenol * The instrument does Effect INNOVA Interference Effect MIRAN Interference + + + + + + + *** + + + + + + + 0 + *** + + 0 + + + + + + + 0 + *** + not read below 0.2 ppm or negative. ** The instrument does not METHODOLOGY To verify this fact, a study was done in a test chamber where the instruments were exposed to formaldehyde in the presence of chemicals suspected of interfering with the readings. A fourth instrument, another type of infrared analyzer (Miran with filament of lithium tantalum LiTaO3), was also tested. ● The response curve of the instruments was checked by generating at least three formaldehyde concentrations to validate the accuracy and precision of the readings. ● Tests were repeated at least three times at each concentration. ● Mixtures (HCHO + chemicals) were generated at well-known concentrations using reference analytical methods: CMS ● Accuracy: ratio of the difference between the average of the readings and the analytical results. ● Precision: average of the standard deviations of the reading. CONCENTRATION / CHEMICALS (TWA) OR MIXING (INTERFERENCE) 6.1 ppm phenol (5 ppm) 3.4 ppm phenol / 0.56 ppm HCHO 65 ppm methanol (200 ppm) 142 ppm methanol / 0.9 ppm HCHO 141 ppm ethanol (1000 ppm) 130 ppm ethanol / 0.6 ppm HCHO 20 ppm toluene (50 ppm) 43 ppm toluene / 1.3 ppm HCHO 53 ppm naphtha VM&P (300 ppm) 64 ppm naphtha VM&P / 1.4 ppm HCHO Ambient air Breathing zone MIRAN CMS Effect * Interference PPM Effect ** Interference 0 + 0 0 + 0 0 + + *** + *** 0 + 0 0 + 0 0 + + + 0 + + + 0 + *** + + read negative. *** Depending on the chemical’s concentration, there are incorrect positive readings or interference. CONCLUSION ● ● ● TWA exposure can be adequately measured: both methods allow measurements in the worker’s breathing zone, and are specific to formaldehyde. Ceiling exposure evaluation is still a problem in cases where other chemicals are present. These four instruments cannot be used as personal dosimeters. Several chemicals can induce an effect or interfere with the reading of these instruments. CHEMICALS Air stream at the top of the chemical at ambient temperature 5%-100% of chemicals’ TWA Charcoal or silica gel Gas chromatography with FID IRSST, MAY 1ST 2006