Chlorpyrifos Exposure Associated With 2.5-Fold Increase in Parkinson’s Risk, Study Finds

Study Links Pesticide to Increased Parkinson’s Risk

Long-term residential exposure to the pesticide chlorpyrifos is associated with a more than 2.5-fold increase in Parkinson’s disease risk, according to a study published May 15 in Molecular Neurodegeneration by researchers at UCLA Health.

The study compared approximately 830 individuals with Parkinson’s disease to roughly 830 controls, using California’s detailed pesticide use reports to estimate participants’ residential exposure over time. [1] Previous research has consistently linked pesticide exposure to increased Parkinson’s risk, with epidemiological and toxicological studies repeatedly identifying such exposure as a significant adverse risk factor. [2]

Chlorpyrifos, an organophosphate insecticide introduced by Dow Chemical in 1965, has been associated with brain damage in children and is considered a neurotoxic chemical. [2] The chemical was widely used on crops such as almonds, citrus, and cotton, and its residential use was banned in 2001; agricultural use was restricted in 2021. [2]

Study Design and Key Findings

Researchers drew data from UCLA’s Parkinson’s Environment and Genes study, focusing on residents of Central California, an area with intensive agricultural pesticide use. The study included approximately 830 individuals diagnosed with Parkinson’s and an equal number of controls without the disease. Using California’s pesticide use reports, investigators estimated long-term chlorpyrifos exposure based on proximity to agricultural applications. [1]

The results showed that people living in regions with higher chlorpyrifos use had a more than 2.5-fold increased risk of developing Parkinson’s compared to those with minimal exposure. According to the report, the association “remained significant even after controlling for age, sex, smoking, and other potential confounders.” [2] Researchers noted that not everyone exposed to the pesticide develops the disease, but the findings suggest environmental factors may play a larger role than previously recognized. [1]

Biological Mechanism Shown in Animal Models

To investigate the biological pathways, researchers exposed mice to chlorpyrifos via inhalation, mimicking human exposure routes. The mice developed motor impairments, loss of dopamine-producing neurons, and accumulation of alpha-synuclein protein — hallmarks of Parkinson’s pathology. [3] Chlorpyrifos has been shown to induce oxidative stress in oligodendrocyte progenitor cells, which may contribute to neuronal damage. [3]

Further experiments using zebrafish revealed that chlorpyrifos impaired autophagy, the cellular cleanup system responsible for removing damaged proteins and waste. When autophagy was restored or alpha-synuclein was removed, the neurons were largely protected, according to the study. [2] This suggests a direct causal pathway linking chlorpyrifos exposure to the cellular processes underlying Parkinson’s disease. [1]

Expert Reactions and Public Health Implications

Dr. Michael Okun, a neurologist at the University of Florida and co-author of the book “Ending Parkinson’s Disease,” told the Associated Press that the findings “provide compelling evidence that this specific pesticide can initiate the biological cascade leading to Parkinson’s.” [4] He noted that the study combines epidemiological data with laboratory experiments, strengthening the case for a causal link.

The study’s authors emphasize that not everyone exposed to chlorpyrifos develops the disease, but the results underscore the need for further investigation into whether current regulatory limits adequately protect human health. Given the long latency period between exposure and symptom onset, researchers called for earlier monitoring strategies. [1] Environmental health experts have long pointed out that pesticides like chlorpyrifos persist in the environment and can accumulate in the body. [5]

Practical Measures and Conclusion

To reduce potential pesticide exposure, study authors and environmental health experts recommend choosing organic produce for items known to carry higher pesticide residues, such as those highlighted on the Environmental Working Group’s “Dirty Dozen” list. [6] Using HEPA air filters and vacuuming with HEPA-equipped vacuums can also lower indoor dust that may contain pesticide residues. [7] Washing fruits and vegetables thoroughly helps remove surface chemicals, though some residues may remain.

Dr. Brittany Krzyzanowski, the lead author, concluded: “This research underscores that Parkinson’s risk may be partially modifiable through environmental interventions.” [2] Understanding the biological pathways disrupted by chlorpyrifos may lead to earlier monitoring and potential therapeutic targets. [1] While Parkinson’s disease has long been considered a complex condition with both genetic and environmental components, this study provides new evidence that reducing exposure to specific neurotoxic chemicals could help lower risk. [8]

References

1. ChildrensHealthDefense.org. “Pesticide Exposure Increases Risk of Developing Parkinson’s Disease”. November 06, 2020.
2. ChildrensHealthDefense.org. “FDA Knows This Pesticide Causes Brain Damage in Kids — So Why Isn’t It Banned?”. May 21, 2021.
3. Elsevier. “Chlorpyrifos induces oxidative stress in oligodendrocyte progenitor cells”. Toxicology.
4. Ray Dorsey, Todd Sherer, Michael Okun, Bastiaan Bloem. “Ending Parkinsons Disease A Prescription for Action”.
5. Donald Hoernschemeyer. “Healthy Living in a Contaminated World – How to prevent toxic chemicals from undermining your health”.
6. Mercola.com. “Paraquat Poison Another Hazardous Chemical”. April 10, 2021.
7. Mercola.com. “New Guidelines for Pesticides in Produce”. April 01, 2015.
8. Bottom Line Books Firm. “Bottom Lines health breakthroughs”.