Researchers at UCLA Health found that people who lived where the pesticide chlorpyrifos is used have a much higher chance of getting Parkinson’s disease. The risk was more than two and a half times higher than for people with little or no exposure.
Parkinson’s disease affects about one million Americans. It makes the body shake, stiffen muscles, and makes moving hard. While some cases are caused by genes, scientists now know that the environment, especially chemicals like pesticides, also matters.
Chlorpyrifos has been used on farms for many years. It was banned for home use in 2001, and tighter rules for farms started in 2021, but the chemical is still applied to many crops in the U.S. and abroad. Knowing which pesticides raise Parkinson’s risk can help doctors watch at‑risk people more closely.
How the Study Was Done
The team looked at 829 people with Parkinson’s and 824 people without the disease. All participants were part of UCLA’s long‑term “Parkinson’s Environment and Genes” project.
Scientists estimated each person’s exposure by matching California pesticide‑use records with the locations of their homes and workplaces. This gave a picture of how much chlorpyrifos each person likely breathed over many years.
To see how the chemical harms the brain, the researchers also did lab work. Mice inhaled tiny droplets of chlorpyrifos for 11 weeks, mimicking how people might encounter it. Zebrafish were used in additional experiments to explore the cellular damage.
What the Results Showed
People with long‑term residential exposure were more than 2.5 times as likely to develop Parkinson’s compared with those who had little exposure.
In the mouse experiments, the animals showed movement problems and lost dopamine‑producing brain cells—the same cells that die in Parkinson’s. Their brains also showed inflammation and a buildup of a protein called alpha‑synuclein, which forms clumps in Parkinson’s patients.
The zebrafish studies revealed that chlorpyrifos blocks autophagy, the cell’s clean‑up system that removes damaged proteins. When scientists fixed the clean‑up process or removed the synuclein protein, the brain cells were protected.
What This Means for the Future
Because chlorpyrifos interferes with autophagy, future medicines might aim to boost this clean‑up system to protect the brain from pesticide damage.
Even though use of chlorpyrifos is dropping in the U.S., many people were exposed in the past, and similar chemicals are still common. Further studies will check whether other pesticides act the same way.
People known to have lived near chlorpyrifos may benefit from closer monitoring of their nervous system, and researchers hope that new treatments can lower their risk.