Estimating Absorbed Dose of Pesticides in a Field Setting Using Biomonitoring Data and Pharmacokinetic Models

Abstract

Linking biomarker data to pharmacokinetic (PK) models permits comparison of absorbed dose with a toxicological benchmark, which is an important step to understanding the health implications of pesticide exposure. The purpose of this analysis was to evaluate the feasibility of reconstructing the absorbed dose of two pesticides using PK models developed from biomarker data in a study of occupational application of these compounds. Twenty-four-hour urine samples were collected from farmers 24 h before through 96 h after a typical application of chlorpyrifos or 2,4-D. PK models were used to link the amounts found in urine samples to absorbed dose. Modeled total body dose estimates (in micrograms) were compared to measured dose from time 0-96 h. Despite the complexities surrounding the interpretation of biomonitoring data from a field setting, the models developed as part of this analysis accurately estimated the absorbed dose of 2,4-D and chlorpyrifos when collection of urine samples was largely complete. Over half of the farmers were excluded from modeling due to suspected noncompliance with urine collection or confounding exposure events, which highlights the importance of these issues for designing and interpreting biomonitoring data in future studies. Further evaluation of PK models in scenarios using single void samples is warranted for improving field-based dose assessments.

Assessment of Health Risk in Human Populations Due to Chlorpyrifos

“…Scher et al [26] reported equivalent chlorpyrifos mass (µg), taken up during a spraying event with twelve farmers in South Carolina and Minnesota. The participants were randomly selected during 2000 and 2001 from licensed pesticide applicators, recruited in a survey known as the Farm Family Exposure Study.…”

“…Scher et al [26] reported that some farmers were excluded from the study since they operated from an enclosed cab while spraying the pesticide. Further Scher et al [26] reported that the usage of granular formulations would be expected to result in less exposure.…”

“…This is due to the estimation of TCP being corrected for the occurrence of TCP pre-event. The TCP representing overall acute exposure is obtained by summation of the values obtained from the five days post-exposure urine samples [26].…”

“…Most of the Sri Lankan and Vietnamese farmers were not using personal protective equipment and had a greater potential for exposure due use of personal individual hand operated sprayers [2]. In contrast, USA farmers used ground booms and tractor mounted spreaders [26] which provide a higher level of protection to the applicator.…”

“…Evaluation of acute exposure after a chlorpyrifos spraying event was carried out using a modified procedure [26] and using the acute exposure guidelines in Table 1, e.g., ARfD. Urine samples were provided before an event (pre-application) representing the baseline exposure, as well as five daily samples after the event (post-application) representing the exposure due to the event.…”