Assessment of Chlorpyrifos Exposure By Passive Dosimetry and Biomonitoring in Pesticide Workers
Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), the U.S. Environmental Protection Agency (EPA) has the authority to regulate the use of pesticides to prevent unreasonable adverse human health effects associated with pesticide exposure. Accordingly, the EPA requires pesticide registrants to perform studies evaluating the potential for pesticide handler exposure. DData from five such studies where exposure that included exposure measurements based on both external measurements and biological monitoring were was used to examine methods of assessment, routes, and determinants of exposure and dose to the pesticide chlorpyrifos. Eighty workers across four job classes were included: Mixer/Loaders (M/L, n=24), Mixer/Loader/Applicators (M/L/A, n=37), Applicators (A, n=9), and Re-entry Scouts (RS, n=10). Results showed that doses were highly variable and differed by job class (p<0.05) with median total (inhalation and dermal combined) exposure-derived absorbed doses (EDADtot) of 129, 88, 85, and 45 ?g/application for A, M/L/A, M/L, and RS, respectively. Doses derived from the measurement of 3,5,6-trichloro-2-pyridinol (3,5,6-TCP) in urine were similar in magnitude but differed in rank with median values of 275, 189, 122, and 97 ?g/application for A, M/L, RS, and M/L/A, respectively. The relative contribution of dermal to inhalation exposure was examined by their ratio. The median ratios of exposure-derived absorbed dermal dose (EDADderm) (assuming 3% absorption) to exposure-derived absorbed inhalation dose (EDADinh) (assuming 100% absorption) across job classes were 1.7, 1.5, 0.44, and 0.18 for RS, M/L, A, and M/L/A, respectively, with an overall median of 0.6. For 34 of 77 workers (44%), this ratio exceeded 1.0, indicating the significance of the dermal exposure pathway. Different dermal absorption factor (DAF) assumptions were examined by comparing EDADtot to the biomarker-derived absorbed dose (BDAD) as a ratio where EDADtot was calculated assuming a DAF of 1, 3, and 10%. Median rFor these same job classes, dDermal exposure dramatically tended to greatly exceeded inhalation exposure (based on potential dose, i.e., assuming 100% absorption) as evidenced by across these same job classes with median dermal to inhalation ratios of 6, 52, 15, and 55, respectively. The overall median ratio was 16 and for 84% of all workers this The ratio s ranged from 0.03 to 76,645 with a median of 16, with 84% of workers having ratios exceededing uatios of 0.45, 0.71, and 1.28, respectively, were determined. This data supports a DAF in the range of 3 to 10%. A simple linear regression of urinary 3,5,6-TCP against EDADtot indicates a positive association explaining 29% of the variability in the 3,5,6-TCP derived estimate of dose. A multiple linear regression model including the variables EDADderm, EDADinh, and application type (i.e. handwand, groundboom, aerial, or corn planter) explaineds 46% of the variability (R2=0.46) in the urinary dose estimate. EDADderm was a marginally significant (p=0.066) while EDADinh was not (p=0.57). The EDADderm regression coefficient (0.0006) exceeded the coefficient for EDADinh (0.00001) by a factor of 35. The dermal coefficient was also more highly significant than inhalation (p=0.067, p=0.586, respectively), again indicating the importance of dermal exposure among these workers. This study supports a DAF in the range of 3 to 10% and demonstrates the value of the pesticide registrant database for the purpose of evaluating pesticide worker exposure. It highlights the significance of the dermal exposure pathway, and identifies the need for methods and research to close the gap between external and internal exposure measures.