Chlorpyrifos and Parkinson's Disease
Chlorpyrifos left American homes in 2001, but it never fully left American farms. Researchers at UCLA Health now tie years of living near its use to sharply higher odds of Parkinson's disease. Their study in the journal Molecular Neurodegeneration found that long-term residential exposure to the insecticide came with more than 2.5 times the risk, and lab work showed how the chemical harms brain cells.
Key Takeaways
- People with long-term residential exposure to chlorpyrifos had more than 2.5 times the risk of Parkinson's disease compared with unexposed people.
- Mice that inhaled the pesticide for 11 weeks lost dopamine-producing neurons, developed movement problems and showed brain inflammation.
- Zebrafish experiments pointed to a broken cellular cleanup process, autophagy, as the way chlorpyrifos damages neurons.
Tracing Exposure Through Addresses
The team drew on UCLA's long-running Parkinson's Environment and Genes study. It compared 829 people with Parkinson's disease against 824 people without it.
No one wore a sensor. Instead, researchers combined California's detailed pesticide use reports with each participant's home and work addresses. That let them estimate how much chlorpyrifos each person had likely been exposed to over many years.
Long-term exposure at home stood out. Those participants carried more than two and a half times the risk of developing the disease.
From Statistics to Cells
An association alone cannot prove cause, so the researchers turned to animals. Mice breathed aerosolized chlorpyrifos for 11 weeks, a method chosen to mimic how people encounter it near fields.
The exposed mice developed movement problems. They lost dopamine-producing neurons, the same cells that die in people with Parkinson's. Their brains showed inflammation and abnormal buildup of alpha-synuclein, a protein that clumps in the disease.
Zebrafish experiments narrowed down the mechanism. Chlorpyrifos disrupted autophagy, the process cells use to clear out damaged proteins. When researchers restored that cleanup or removed the synuclein protein, the neurons survived.
Senior author Jeff Bronstein, a professor of neurology at UCLA Health, called chlorpyrifos “a specific environmental risk factor for Parkinson's disease,” rather than one more member of a broad chemical class. He said the animal results make a causal link likely.
What Comes Next
The autophagy finding gives drug developers a target. Treatments that boost the cell's cleanup system might protect neurons in people with heavy past exposure. The authors also suggest that people with known historical exposure could benefit from closer neurological monitoring.
Future studies could test whether other common pesticides harm neurons the same way. UCLA's earlier screening work already identified 10 pesticides that were directly toxic to the neurons lost in Parkinson's.
A Pesticide Regulators Keep Revisiting
Nearly one million Americans live with Parkinson's disease. Genes explain only part of the risk, and environmental exposures draw growing attention. Chlorpyrifos is a useful test case because its legal status has swung back and forth. US residential use ended in 2001. The Environmental Protection Agency revoked all food-crop tolerances in 2021, a federal appeals court later vacated that rule, and the agency reinstated the tolerances in 2024 before proposing to limit use to a shorter list of crops. A regulatory tracker lists each turn. Meanwhile, the chemical remains in wide use in many other countries.
That history matters for anyone who lived near treated fields before the restrictions. Researchers note that many people were exposed in the past, and that similar pesticides are still common. Concerns about who is most at risk from pesticide exposure are not new, and the search for alternative pesticides and gentler ways to protect crops continues alongside this kind of research.
Written by Vytautas Valinskas