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Introduction: Organochlorine insecticides (OCs) are a class of pesticides historically used to control for insects in agriculture worldwide and that are still used in developing countries today for the control of vector borne illnesses. OCs were mostly banned in the United States in the 1970s and 1980s, with lindane and endosulfan having only been banned recently in 2006 and 2010, respectively. The strongest epidemiologic evidence for OC insecticide exposures and cancers comes from occupational and population-based studies of lymphohematopoietic cancers, specifically non-Hodgkin lymphoma (NHL). Many population-based studies evaluating OCs have focused on breast cancer, but the majority of these results have been inconsistent. While most epidemiologic studies of OCs have included male pesticide applicators, few analyses have included female spouses of pesticide applicators, warranting further research to examine the impact of OC exposures on the risk of female-specific cancers. Female spouses of pesticide applicators may be exposed to OC insecticides from their personal use (i.e., mixing/applying of pesticides), and indirect exposure from non-occupational expo¬¬¬sure pathways (i.e., agricultural drift, take-home and residential use). The following projects will explore the impact of both personal use and non-occupational exposures to seven OCs (i.e., aldrin, chlordane, dieldrin, DDT, heptachlor, lindane and toxaphene), with risk of cancer among the Agricultural Health Study (AHS) farm spouses (n=32,345).
Methods: My first aim is to conduct an epidemiologic analyses to examine associations between the AHS farm spouses’ personal use of each of seven OCs with total and specific cancers. My second aim is to characterize the AHS farm spouses’ non-occupational OC exposures to each of the seven OCs by applying an active ingredient-specific exposure algorithm recently developed by AHS researchers. My third aim is to conduct a second epidemiologic analysis examining the associations between the AHS farm spouses’ non-occupational exposures on their risk of developing breast cancer. Together, these aims will elucidate the impact of exposures to seven individual OCs, through personal use and multiple non-occupational exposure pathways, on the risk of cancer among the AHS farm spouses.
Results: In the first aim, most cancers were not associated with OC use. Risk of glioma was increased among users of at least one OC and specifically among lindane users. Multiple myeloma was also associated with chlordane. There were also positive associations between pancreatic cancer and lindane, and ER-PR- breast cancer and dieldrin. The second aim identified an additional 1.2-10.0% of female farm spouses exposed to individual OCs through individual non-occupational pathways. In addition, I captured variability in OC exposure intensities among the AHS spouses, with ratios of the 75th to 25th percentiles ranging from 2.8 to 8.5. The agricultural drift and take-home pathway estimates were highly correlated with each other across all OCs (rs ≥ 0.98). The residential use pathway was not correlated with either the agricultural drift nor take-home pathways for chlordane or heptachlor (rs < 0.02), which were the only OCs with residential use. In the third aim, most individual exposure pathways of individual OCs were not associated with breast cancer overall or with ER+PR+ breast cancer. Toxaphene exposure through the take-home pathway was associated with ER+PR+ breast cancer. Aldrin and toxaphene exposures through the agricultural drift pathway were associated with overall and ER+PR+ breast cancers. Chlordane and heptachlor exposures through the residential use pathway were associated with ER+PR+ breast cancer. Finally, overall non-occupational exposures of aldrin, heptachlor and toxaphene were associated with ER+PR+ breast cancer.
Discussion: This dissertation has demonstrated that exposures to OCs through their personal use and through non-occupational pathways may contribute to an increased cancer risk among female farm spouses of pesticide applicators. Prior to this study, few analyses have examined OC insecticide use and cancer risk among female spouses of pesticide applicators. In addition, studies which have evaluated cancer associations with non-occupational pesticide exposures have been limited by surrogate measurements, unavailable questionnaire information, and non-specific biological markers. Furthermore, the studies presented herein may help to inform future risk analyses of OC exposures and cancer outcomes, as well as future exposure assessments of non-occupational OC exposures among farm women.

ETD_9821

Ph.D.

Includes bibliographical references

doi:10.7282/t3-cxv2-0976

ETD doctoral

The author owns the copyright to this work.