Long residential exposure to chlorpyrifos tracked more than double the Parkinson's risk in a California cohort

What the research found

ScienceDaily posted this on 1 November 2026 from UCLA Health. Hasan and colleagues, with senior author Jeff Bronstein, report in Molecular Neurodegeneration. The release prints the journal citation as 2025; 21 (1), DOI 10.1186/s13024-025-00915-z. This card uses the 1 November 2026 news date and does not reconcile the year printed in the DOI. In the Parkinson's Environment and Genes study, 829 people with Parkinson's and 824 without it were compared. Prolonged residential exposure to chlorpyrifos was associated with more than 2.5 times the risk. The population comparison alone is not proof of cause. Address histories covered home and work, using California pesticide records. Mice that inhaled the chemical as an aerosol for 11 weeks developed movement problems, lost dopamine neurons, showed brain inflammation, and accumulated alpha-synuclein. In zebrafish, the chemical disrupted autophagy, the cell cleanup of unwanted proteins. Restoring that cleanup, or removing synuclein, protected neurons in those experiments. Bronstein said the work identifies chlorpyrifos specifically, not pesticides as a class, and that the animal mechanism makes the association look causal. He also pointed to possible future strategies. Those protective findings are from the lab, not a human therapy. Residential use was banned in the United States in 2001, with further agricultural restrictions in 2021. The chemical is still used on many crops in the United States and in other countries. Parkinson's affects nearly one million Americans. Not medical advice.

Evidence level: Animal study. Results in animals or cells often don't carry over to people.

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