Environmental and Occupational Agricultural Exposures and Risk of Childhood Cancer

Introduction: Agricultural exposures are diverse and may occur in environmental and occupational settings. Pesticides have been a major concern and several studies have reported positive associations between maternal occupational and environmental exposure to pesticides and childhood cancer risk. Exposure to farm animals is another component of agricultural exposures that has been found in some studies to be associated with childhood cancers. Exposure to biological dust is common in agricultural occupations and may provide a useful, although non-specific, measure of exposure for evaluating potential associations between agriculture and childhood cancer risk. Projects explored in this dissertation address each of these agricultural exposures in order to examine the potential role of agriculture in childhood cancer risk. Methods: The first aim was to examine the association between crop density by crop type and childhood cancer risk (Chapter 2). Limited research has been conducted on crop density and many crops have not yet been explored in relation to childhood cancer. The second aim was to examine the impact of parental occupational exposures to pesticides, farm animals, and biological dust on childhood cancer (Chapter 3). The final aim was to explore associations between densities of farm animal species, animal operations, and childhood cancer risk (Chapter 4). Results: In the first aim, we found significant associations between specific crop types and sub-types of childhood leukemia. In our second aim, we found no associations between maternal or paternal occupational exposure to pesticides or farm animals. Positive associations were observed between mothers occupationally exposed to biological dust, which were also significant when occupations with pesticide and farm animal exposure were removed from the biological dust grouping. No associations were found for fathers occupationally exposed to biological dust, but positive associations were observed when either parent was exposed. In the final aim, we found associations between densities of specific animals, animal operations, and risk of childhood cancer. Discussion: Environmental and occupational agricultural exposures increase the risk of cancer in children. Future epidemiologic studies using high-quality individual-level estimates of agricultural exposures are needed to verify our results and to further the understanding of agriculture as it relates to childhood cancer.