A pesticide used in the US food supply may raise Parkinson’s risk, with research suggesting long-term exposure could increase the chance of the disease.
The study compared 829 people with Parkinson’s to 824 people without the disease over a 45-year period, focusing on their proximity to chlorpyrifos, a chemical used on crops including soybeans, fruit and nut trees, broccoli, cauliflower and other row crops.
In humans, long-term exposure to the pesticide was linked to more than 2.5 times higher risk of Parkinson’s, a neurological condition that affects movement.
A UCLA study also included experiments in mice and zebrafish.
Mice that inhaled the pesticide for 11 weeks developed movement problems similar to Parkinson’s symptoms, loss of dopamine-producing neurons, which are nerve cells that help control movement, increased brain inflammation and a build-up of harmful proteins.
Zebrafish suffered brain cell death and damage linked to failure in the cell’s waste removal system.
Dr Jeff Bronstein, director of the Movement Disorders Program at UCLA and professor of neurology and molecular toxicology, said previous human studies had also suggested an association between chlorpyrifos exposure and Parkinson’s.
He said: “[We were] surprised that the mechanism of toxicity was apparent in both mice and zebrafish. We rarely find such consistent results in different animal models.”
Bronstein described the association between pesticide exposure and Parkinson’s as “very strong”, adding that the longer someone was exposed, the higher the risk became.
He advised: “People should avoid exposure to CPF and similar pesticides (organophosphates) by not using them in their home, eating organics, and washing fruits and vegetables before eating them.”
The researchers acknowledged several limitations.
The study was observational, meaning it showed an association but could not prove causation.
Exposure was estimated from participants’ locations rather than measured directly, and factors such as diet, indoor exposure and personal lifestyle behaviours were not included.
Findings from animal models also cannot be directly applied to humans.
The study also noted that chlorpyrifos may have been used alongside other chemicals, making its specific effect harder to isolate.
Chlorpyrifos is used to control pests including termites, mosquitoes and roundworms, and people can be exposed by breathing it in or by consuming contaminated food or water.
In the US, the Environmental Protection Agency banned the use of chlorpyrifos on food crops in 2021, but a federal appeals court overturned that decision in 2023, allowing its use to resume on some crops while regulators revisit the rule.
In January 2026, the agency outlined plans to move forward with a rule that would ban most uses of chlorpyrifos.
The EPA said: “EPA is currently developing a revised human health risk assessment for chlorpyrifos as part of that review, and will consider this study alongside any other relevant submissions. Where the science calls for stronger protections or tolerance revocations, EPA will act without hesitation and without delay.”
Corteva, an Indiana agrichemical company formed in 2019 through the merger of Dow Chemical and DuPont, announced in 2020 that it would end production of chlorpyrifos, citing declining sales.
In April 2022, German chemical company BASF requested the cancellation of its pesticide registrations for products containing chlorpyrifos.
BASF said it does not manufacture chlorpyrifos and does not have any pesticide registrations issued by the US EPA for chlorpyrifos-containing products.
No products from Corteva or BASF were included in the study linking chlorpyrifos to Parkinson’s disease.
