Groundwater pesticide levels and the association with Parkinson disease.

It is unclear whether exposure to environmentally relevant levels of pesticides in groundwater is associated with an increased risk of Parkinson disease (PD). The purpose of this study was to examine the relationship between PD and pesticide levels in groundwater. This cross-sectional study included 332 971 Medicare beneficiaries, including 4207 prevalent cases of PD from the 2007 Colorado Medicare Beneficiary Database. Residential pesticide levels were estimated from a spatial model based on 286 well water samples with atrazine, simazine, alachlor, and metolachlor measurements. A logistic regression model with known PD risk factors was used to assess the association between residential groundwater pesticide levels and prevalent PD. We found that for every 1.0 µg/L of pesticide in groundwater, the risk of PD increases by 3% (odds ratio = 1.03; 95% confidence interval: 1.02-1.04) while adjusting for age, race/ethnicity, and gender suggesting that higher age-standardized PD prevalence ratios are associated with increasing levels of pesticides in groundwater.