THOMPSON STUDIES GROUP -- Pesticide Exposure Study

Reducing Pesticide Exposure in Children of Farm Workers

Organophosphate pesticides (OPs) continue to be widely used in the United States. There is little doubt that OPs are related to ill health among adults, especially farmworkers who are exposed to OPs as part of their regular work. Even more disturbing, however, is that farmworkers’ families, including children, are exposed to pesticides through the take-home pathway.

Pesticide Health Impacts

Part I

The overall goal of this portion of the pesticides project was to reduce the levels of pesticide exposure in children of farmworkers in the Yakima Valley of Washington state by breaking the pesticide “take-home” pathway. The specific aims to achieve this goal were:

  • Develop a culturally-appropriate intervention to break the pesticide take-home pathway;
  • Conduct a randomized, controlled trial to evaluate the effectiveness of the intervention as assessed by examining changes in the urinary organophosphate pesticide metabolites of children between the ages of 2 and 6 who reside with farm workers;
  • Assess the secondary effects of the intervention by examining changes in pesticide concentrations in house dust in the residential environments of farmworkers and car dust of the farmworkers; changes in the urinary organophosphates pesticide metabolites of farm workers; and changes in self-reported knowledge, attitudes, and practices of farmworkers regarding protection from pesticide exposure for children.
Spraying pesticide

Part II

The overall goal of this part was to investigate multiple pathways that may contribute to pesticide exposure in adults and children living in agricultural communities. The specific aims were:

  • Examine four main pathways of potential exposure to OP pesticides
  • Compare levels of OP pesticide urinary metabolites in farmworkers and their children and non-farmworkers and their children, adjusting for the multiple pathways
  • Compare levels of OP pesticide parent compounds in the bloods of adult farmworkers and non-farmworkers, adjusting for the multiple pathways.
  • Conduct outreach and dissemination activities, and evaluate those activities in the community.

Part III

This pathway has been demonstrated in our previous studies and children of farmworkers have been shown to have a threefold increase of dimethyl urinary pesticide metabolites compared to non-farmworker children in an agricultural area. In the past ten years of our Child Health Center (CHC) much has been learned about pesticide exposure and how pesticides are metabolized. It is known, for example, that individuals who have low levels of PON1 paraoxonase activity are slow metabolizers of some OP metabolites, making them more sensitive to the toxicity of certain OPs (for example, chlorpyrifos [CP] and chlorpyrifos oxon [CPO] versus azinphosmethyl (AZ) and its oxon (AZO), where such differences were less important). Our characterizations and those of our collaborators in the CHC have analyzed the episodic nature of OP usage in the agricultural practice in.

These observations, which are highly relevant for most agricultural regions in the US where four seasons exist, show the importance of characterizing both the within- and between-person variability in pesticide exposure and response. Past research on OP exposure has focused on limited sample collection; frequently, two or three “spot” samples (samples taken at one time during the day) gathered during limited times of the year, and thus have failed to adequately address factors related to individual and population level variability.

Common to all these studies has been the large within-person variability of the samples which reduces power to detect which factors are statistically significant between seasons; further, such evaluations have limited ability to identify highly exposed populations. In this project, we will address all three of these areas; specifically, we will:

  • Characterize the seasonal variability of OP exposure across our cohort by sampling at times of peak OP usage and by evaluating OP metabolite profiles across time during these seasons;
  • Assess the influence of gene environment interactions on OP exposure and response profiles; and
  • Calculate the contributions from gene, environment and season to within-person and between-person variability of the urinary OP metabolites in farmworkers to identify quantitatively differences between persons and across seasons