A common agricultural pesticide may significantly increase the risk of developing Parkinson's disease, according to new research from UCLA. Scientists found that people with long-term residential exposure to chlorpyrifos were more than 2.5 times more likely to develop the condition compared to those without exposure. The study, published in Molecular Neurodegeneration, combined evidence from hundreds of people with laboratory experiments to uncover exactly how the pesticide harms critical brain cells involved in movement control.

What Is Chlorpyrifos and Why Should You Care?

Chlorpyrifos has been used on agricultural crops for decades. Although residential uses were banned in 2001 and agricultural applications faced restrictions in 2021, the chemical continues to be used on various crops in the United States and remains common in many other countries. Because exposure can occur over many years, researchers are concerned that people who lived near treated fields may face long-term health consequences, even decades after the initial exposure.

Parkinson's disease is a progressive neurological disorder affecting nearly one million Americans. The condition develops when specialized brain cells that produce dopamine gradually die off. Dopamine is a chemical messenger that helps control movement, coordination, and balance. As dopamine levels decline, people may experience tremors, muscle stiffness, slowed movement, and difficulty maintaining balance.

How Did Researchers Discover This Connection?

To investigate the link between chlorpyrifos and Parkinson's disease, researchers analyzed data from 1,653 people enrolled in UCLA's ongoing Parkinson's Environment and Genes study. The group included 829 people diagnosed with Parkinson's disease and 824 individuals without the condition. The team estimated each participant's long-term exposure to chlorpyrifos by combining California pesticide use records with residential and workplace addresses, allowing researchers to determine who had likely experienced greater exposure over time.

The findings revealed a striking pattern. Individuals with long-term residential exposure to chlorpyrifos had more than 2.5 times the risk of developing Parkinson's disease compared with people who were not exposed.

How Does the Pesticide Damage the Brain?

To better understand why this increased risk occurs, researchers conducted a series of laboratory experiments. Mice were exposed to aerosolized chlorpyrifos for 11 weeks using inhalation methods designed to mimic the way people typically encounter the pesticide in the environment. The exposed animals developed movement problems and lost dopamine-producing neurons, the same type of brain cells that degenerate in Parkinson's disease.

Researchers also observed signs of inflammation in the brain and an abnormal buildup of alpha-synuclein, a protein strongly associated with Parkinson's disease. In patients with the disorder, alpha-synuclein can accumulate into clumps that interfere with normal brain function. Additional experiments in zebrafish helped uncover the biological mechanism behind the damage.

Understanding the Brain's Cleanup System

The key discovery involves a process called autophagy, often described as the cell's internal cleanup and recycling system. Autophagy removes damaged proteins and cellular debris before they can accumulate and cause harm. Researchers found that chlorpyrifos interferes with this critical cleanup process.

When autophagy was disrupted in the laboratory, neurons became more vulnerable to injury. However, when scientists restored autophagy or removed synuclein protein, the nerve cells were protected from damage. These results suggest that the pesticide may contribute to Parkinson's disease by preventing cells from clearing away harmful material, allowing toxic proteins to build up over time.

Steps to Protect Your Brain Health

• Know Your Exposure History: If you lived or worked near agricultural areas where chlorpyrifos was used before restrictions, consider discussing your exposure history with a neurologist, especially if you have family members with Parkinson's disease.
• Monitor for Early Symptoms: Be aware of early signs of Parkinson's disease, including tremors, muscle stiffness, slowed movement, or difficulty with balance, and report them to your doctor promptly.
• Seek Specialist Evaluation: If you have known past exposure to chlorpyrifos, ask your doctor about neurological monitoring, particularly as researchers continue investigating the long-term effects of pesticide exposure on brain health.

"This study establishes chlorpyrifos as a specific environmental risk factor for Parkinson's disease, not just pesticides as a general class. By showing the biological mechanism in animal models, we've demonstrated that this association is likely causal. The discovery that autophagy dysfunction drives the neurotoxicity also points us toward potential therapeutic strategies to protect vulnerable brain cells," said Dr. Jeff Bronstein, professor of Neurology at UCLA Health and the study's senior author.

Dr. Jeff Bronstein, Professor of Neurology at UCLA Health

What Comes Next for Parkinson's Research?

The discovery highlights autophagy as a potential target for future treatments aimed at protecting the brain from pesticide-related injury. Researchers note that chlorpyrifos use has declined in recent years in the United States, but many people experienced exposure before restrictions were introduced. In addition, similar pesticides continue to be used around the world.

Future studies will explore whether other commonly used pesticides disrupt autophagy in the same way and whether treatments that strengthen the cell's natural cleanup systems could reduce Parkinson's risk among exposed individuals. The findings also suggest that people with known past exposure to chlorpyrifos may benefit from closer neurological monitoring as researchers continue to investigate the long-term effects of pesticide exposure on brain health.