Long-term exposure to chlorpyrifos near the home was linked to a more than 2.5-fold higher risk of developing Parkinson's disease, according to UCLA Health researchers whose findings were published in Molecular Neurodegeneration. The study points to a common pesticide still used on crops as a possible contributor to a disease that affects nearly one million Americans.
The researchers drew on data from 829 people with Parkinson's disease and 824 without it, all enrolled in UCLA's ongoing Parkinson's Environment and Genes study. They estimated long-term exposure by combining California pesticide use records with residential and workplace addresses, a method that let them tie risk not just to broad county-level patterns but to where people actually lived and worked.
That detail matters because the exposure the team focused on was not a vague past contact but long-term living near where chlorpyrifos was applied. Residential uses of the chemical were banned in 2001, and agricultural applications faced restrictions in 2021, yet it remains in use on a variety of crops in the United States and in many other countries. The finding lands in the middle of an unresolved public health question: how much exposure is enough to matter, and who is still being exposed now?
The laboratory work strengthened the human data. In mice exposed to aerosolized chlorpyrifos for 11 weeks through inhalation methods designed to mimic environmental exposure, researchers saw movement problems, loss of dopamine-producing neurons, inflammation in the brain and an abnormal buildup of alpha-synuclein. Parkinson's disease develops when those dopamine-producing brain cells gradually die off, which is why the animal results matter even though they do not explain every step of the injury.
What the study still does not pin down is the exact mechanism that turns chlorpyrifos exposure into neuron loss in humans. It does, however, sharpen the case that long-term residential exposure is the part of the risk most clearly tied to the disease in this dataset, because that is the exposure the researchers measured by residence and workplace history. For people who lived for years near treated fields, the question is no longer whether the chemical is common. It is how much of that common exposure the brain can take before the damage starts.
