The Quantification of Occupational Pesticide Exposure and Associated Effects on Human Health, with Special Consideration for Social Determinants

Abstract

Researchers first linked pesticide exposure to cancer development more than 50 years ago. Overall, exposure to pesticides such as chlorpyrifos (CPF) and other organophosphate pesticides (OPP) have been associated with increased risk of numerous cancers such as colorectal, esophageal, brain, and lung cancer. Today it is estimated that in low and middle income countries (LMICs), 2 to 8% of all cancers are thought to be due to occupational carcinogen exposure6. Pesticides, especially those persistent in the environment, such as organochlorine pesticides, have also been associated with endocrine disruption that leads to perturbations in metabolism, puberty, and birth defects. Farmworkers and especially migrant workers face unique barriers to healthcare, personal protective equipment, and often have increased exposure, however, the literature is lacking when it comes to quantifying pesticide exposure and understanding the social determinants associated with these exposures. Moreover, there needs to be more attention to specifically how these differences in exposure by social determinants can lead to changes in the human body. This dissertation takes a multi-disciplinary approach to ascertaining pesticide exposure by occupation and understanding the resultant health effects in Thailand, and by quantifying pesticide biomarker and biological activity by farmwork history and citizenship status in the US . The second chapter of this dissertation presents a cross-sectional study completed in Chiang Rai, Thailand with conventional farmworkers and non-farmworkers. In this chapter, pesticide exposure was quantified through air samples and liquid chromatography/mass spectrometry. Differences in self-reported health outcomes, complete blood counts and cholinesterase activity were assessed before and after pesticide spraying. In Chapter 3, the National Health and Nutrition Examination Study (NHANES) publicly accessible data was queried from 1999-2014 for pesticide exposure biomarker concentrations among farmworkers and non-farmworkers by citizenship status. Next in Chapter 4, NHANES data from Chapter 3 was combined with publicly available toxicity assay data from the US Environmental Protection Agency’s (EPA’s) Toxicity Forecast Dashboard (Toxcast). By linking human population exposure data in NHANES to dose-response data from Toxcast, we estimated adverse biological effects that occur across a range of human population-relevant pesticide doses. In the Chapter 2 study, we detected the pesticides methomyl, ethyl chlorpyrifos, and metalaxyl via personal air sampling. Farmworkers in Northern Thailand had significant alterations in stress measures and clinical biomarkers, including decreased blood cell counts and cholinesterase activity, relative to matched controls. These changes were associated with occupational pesticide exposures. None of the farmworkers wore standardized PPE for the concentrated chemicals they were sprayed. Improving PPE use in LMICs presents a likely route for preventive intervention. Based on Chapter 3 NHANES outcomes, disparities exist in pesticide exposure by farmwork history and US citizenship present. Citizenship status and farmwork history were significantly associated with increased exposure for specific pesticides. In Chapter 4, NHANES participants are exposed to biologically active pesticide exposure concentrations based on the Toxcast in vitro assay testing data. In these last two aims, we found that nearly all participants had pesticide biomarkers in their urine or blood, and non-citizen farmworkers are more likely to be exposed to all of the pesticides except for 2,5-Dichlorophenol, 2,4-Dichlorophenol, and DEET acid. The results from Chapters 2, 3, and 4 highlight the need for additional research and legislation to reduce these gaps in pesticide exposure and health outcomes.