Residential Proximity to Animal Feeding Operations and Cancer Risk in the Agricultural Health Study

Abstract

Background: Concentrated animal feeding operations (AFOs) are major sources of hazardous emissions into the surrounding environment, but few studies have investigated cancer risk associated with living near intensive animal agriculture.Methods: We evaluated the association between residential proximity to AFOs and cancer risk among licensed pesticide applicators (mostly male farmers) in the Agricultural Health Study cohort. We linked enrollment (1993-1997) addresses for 32,674 participants in Iowa to a statewide database of permitted AFOs that included animal counts standardized by animal size and manure production (animal units; AUs). We created metrics to reflect exposure proximity and intensity, enumerating AFOs and animal density (quartiles of AUs) within 2 and 5km of residences. Cox regression was used to estimate associations (hazard ratio, HR; 95% confidence interval, 95%CI) with incident cancer for major tumor sites, adjusting for demographic and farming-related factors (e.g., raising animals and occupational pesticide exposure).Results: There were 4,741 incident cancers from 1993-2015. We observed increased risk for non-Hodgkin lymphoma among those residing within 5km of at least one AFO (HR=1.9; 95%CI=1.3-3.0), but without a statistically significant trend across AU quartiles (ptrend=0.31). Prostate cancer risk was significantly elevated in the highest AU quartile (HR=1.4; 95%CI=1.1-1.6; ptrend=0.01). Lung cancer associations showed an inverse, monotonic trend with increasing AUs (HRQ4=0.74; 95%CI=0.5-1.1; ptrend=0.04). Adjustment for contact with animals and occupational use of pesticides previously associated with these cancers did not change the results, and patterns were similar for exposures within 2km. We found no associations for other cancers.Conclusions: Our findings suggest that residential proximity to AFOs may influence risk of cancer at certain sites, even after consideration of animal contact and occupational exposure to pesticides.