UCLA Study Links Chlorpyrifos Pesticide Exposure to Higher Parkinson’s Risk

A new UCLA study published in a Springer Nature journal reports that long‑term exposure to the common organophosphate pesticide chlorpyrifos is associated with more than a 2.5‑fold increase in Parkinson’s disease risk, based on a case‑control analysis of 829 Parkinson’s patients and 824 controls tracked over 45 years using residential proximity to spraying as a proxy for exposure. In parallel animal experiments, mice that inhaled chlorpyrifos for 11 weeks developed Parkinson’s‑like movement problems, loss of dopamine‑producing neurons, brain inflammation and harmful protein buildup, while zebrafish exhibited brain‑cell death tied to failures in the cellular ‘cleanup’ system. Lead researcher Dr. Jeff Bronstein said he was struck by the rare consistency across human epidemiology and two different animal models, but emphasized that the human data remain observational and cannot prove causation, and that exposures were estimated rather than directly measured. Chlorpyrifos has been widely used on U.S. crops such as soybeans, fruit and nut trees, and broccoli, and although the EPA banned its use on food crops in 2021, a federal appeals court reversed that decision in 2023, allowing agricultural uses to resume. The authors urge people to avoid chlorpyrifos and related organophosphate pesticides where possible, while acknowledging study limitations including potential co‑exposure to other farm chemicals and the difficulty of translating animal‑model findings directly to humans.