Common Pesticide Linked to Increased Parkinson’s Risk, UCLA Study Finds

A pesticide widely used on American crops has been linked to an increased risk of Parkinson’s disease, according to new research from UCLA. The study, published in Springer Nature Link, suggests that exposure to chlorpyrifos could significantly raise the likelihood of developing the degenerative neurological condition.

The comprehensive research tracked 829 people with Parkinson’s disease and 824 without it over a 45-year period, analyzing their proximity to areas where chlorpyrifos was used. The findings were concerning: long-term exposure to the chemical was associated with more than 2.5 times higher risk of developing Parkinson’s disease.

“We were surprised that the mechanism of toxicity was apparent in both mice and zebrafish,” said Dr. Jeff Bronstein, director of the Movement Disorders Program at UCLA and professor of neurology and molecular toxicology. “We rarely find such consistent results in different animal models.”

The researchers conducted multiple experiments to validate their findings. In laboratory tests, mice exposed to chlorpyrifos through inhalation for 11 weeks – mimicking human exposure patterns – developed movement problems similar to Parkinson’s symptoms. The exposed mice also showed loss of dopamine-producing neurons, increased brain inflammation, and buildup of harmful proteins.

Separate experiments on zebrafish revealed brain cell death and damage linked to failure in the cell’s “cleanup system,” according to the study’s press release.

Chlorpyrifos is commonly applied to agricultural products including soybeans, fruit and nut trees, broccoli, cauliflower, and various row crops. The chemical helps control pests such as termites, mosquitoes, and roundworms. Human exposure typically occurs through inhalation or consumption of contaminated food and water.

Dr. Bronstein emphasized that the association between pesticide exposure and Parkinson’s was “very strong,” with risk increasing alongside duration of exposure. He advised the public to “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 regulatory status of chlorpyrifos has been contentious in recent years. In 2021, the Environmental Protection Agency banned its use on food crops, citing health concerns. However, a federal appeals court overturned that decision in 2023, allowing limited use to resume on certain crops while regulators revisit the rule.

Earlier this year, in January 2026, the EPA announced plans to move forward with regulations that would ban most uses of chlorpyrifos.

“Chlorpyrifos is subject to registration review, a process required under FIFRA (the Federal Insecticide, Fungicide, and Rodenticide Act) in which registered pesticides are comprehensively evaluated every 15 years against current safety standards and the latest scientific evidence,” the EPA said in a statement.

The agency added: “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.”

Some major manufacturers have already begun distancing themselves from the chemical. Corteva, an Indiana agrichemical company formed through the merger of Dow Chemical and DuPont, announced in 2020 that it would end production of chlorpyrifos within the year, citing declining sales. Similarly, German chemical company BASF requested cancellation of its pesticide registrations for products containing chlorpyrifos in April 2022.

The researchers acknowledged some limitations to their study. As an observational investigation, it shows association rather than definitively proving causation. The study estimated exposure based on participants’ locations without measuring dietary intake, indoor exposure, or personal lifestyle behaviors. Additionally, the results from animal models cannot be directly translated to humans, and the potential presence of other chemicals alongside chlorpyrifos makes it difficult to isolate its specific impact.

Despite these limitations, the consistent findings across human observations and animal experiments have raised significant concerns about this widely used agricultural chemical and its potential role in the development of Parkinson’s disease.