Abstract for Poster 23

 

 

Comparative dermal absorption of 2,4-D, mecoprop and dicamba based on field data collected in an occupational setting

S.A. Harris
Department of Epidemiology and Community Health and Center for Environmental Studies, Virginia Commonwealth University, Richmond VA, United States

Background

To assess health risks associated with pesticide exposures, valid estimates of dermal absorption are needed. In situations where no controlled human data are available, animal data may be used to estimate human absorption. Since there can be significant uncertainty in extrapolating these estimates from laboratory animals to man, observational data collected in occupational settings can be used to validate or provide estimates for risk assessment. The human percutaneous aborption of 2,4-dichlorophenoxyacetic acid (2,4-D), a turf herbicide, has been well established in laboratory studies. Little information is available for other commonly used turf herbicides. The objective of this work was to compare urinary concentrations and predicted weekly doses of the herbicides 2,4-D, mecoprop  (2-(2-methyl-4-chlorophenoxy) propionic acid, MCPP) and dicamba (3,6-dichloro-o-anisic acid) to provide estimates of dermal absorption for MCPP and dicamba.

Methods

Two consecutive urine samples (24 hour) and questionnaire data were collected from a group of 98 professional turf applicators from 20 companies across Southwestern Ontario, Canada. Daily pesticide use information, including product, volume, and dilution was recorded for each individual. Measured urinary concentrations of each pesticide and pesticide use information were used to estimate weekly dose (μg) for each individual. Data were analysed using the Statistical Analysis System (SAS) version 9. Following descriptive data analysis, 4 observations were removed from the data set. Correlations and linear regressions were conducted to evaluate relationships between the predicted doses (μg) for each pesticide and their natural log transformed values. Paired t-tests were used to test for differences between absorbed dose.

Results

The predicted arithmetic mean weekly dose of 2,4-D was 3219 μg (geometric mean (GM), 1086 μg) with 95% confidence limits of  2260 μg and 4177 μg.  The mean absorbed dose of MCPP was 4595 μg (95% CL; 3122-6066 μg; GM, 1525 μg) and dicamba averaged 58 μg (95% CL; 40-75; GM, 19.06). The concentrations of 2,4-D, MCPP and dicamba most commonly present in the formulations used were 190, 100 and 18 g/L respectively.  Based on these concentrations, we would expect that the predicted doses of MCPP and dicamba would be approximately 50% and 10% of 2,4-D if dermal absorption is similar for these compounds. Results indicate that the absorbed dose of MCPP was significantly higher than 2,4-D (p<0.001) even though it is present at less than half the concentration in the formulation. Using a value of  6% for the dermal absorption of 2,4-D, predicted dermal absorptions for MCPP and dicamba, based on expected urinary concentrations, are 16.3% and 1.1% respectively.

Conclusions

Result indicate that the dermal absorption of MCPP might be higher than previously expected based on its structure and similarity with 2,4-D. Recognizing that there are limitations in observational studies, field data can supplement data collected in the laboratory and help to provide reasonable estimates of dermal absorption of pesticides for regulatory risk assessment. 

 

Content last modified: 17 May 2005