Parkinson’s disease has long been recognized as a complex condition that arises from a mix of genetic vulnerability and environmental influences. A new study from UCLA Health now adds important detail to that environmental side of the story, suggesting that long term exposure to the widely used pesticide chlorpyrifos may significantly increase the risk of Parkinson’s disease. The research, which links a common pesticide to 2.5 times the risk of Parkinson’s disease, also begins to explain how this chemical harms brain cells and points to a potential strategy for protecting them.

Parkinson’s disease affects nearly one million people in the United States. It is a progressive neurological disorder that gradually damages brain cells responsible for coordinating movement. People living with Parkinson’s often experience tremors, muscle stiffness, slowness of movement, and problems with balance or coordination. A key feature of the disease is the loss of neurons that produce dopamine, a chemical messenger that allows nerve cells to communicate and supports smooth, controlled movement. As dopamine-producing neurons die, the brain loses some of its ability to regulate these movements, which leads to the characteristic motor symptoms of Parkinson’s.

Genetic factors can raise or lower a person’s risk, yet many individuals who develop Parkinson’s do not have a strong family history. This has drawn scientists toward environmental exposures that might contribute to the disease. Pesticides are of particular interest because they are designed to interfere with biological processes in pests and, in some cases, can affect the nervous system in humans as well. Chlorpyrifos is one such pesticide. It has been used extensively in agriculture for decades. Residential uses in the United States were banned in 2001, and agricultural applications were restricted further in 2021, but the chemical remains in use on a variety of crops and continues to be applied in many parts of the world.

One of the challenges in understanding the health impact of a pesticide like chlorpyrifos is that exposure can occur many years before symptoms appear. People may encounter low levels over long periods, often without realizing it, especially if they live or work near treated fields. The UCLA team set out to examine whether long term residential exposure to chlorpyrifos was associated with a higher chance of developing Parkinson’s disease and then to explore how this pesticide might affect the brain at a cellular level.

The researchers drew on data from the Parkinson’s Environment and Genes study, a long running project at UCLA that investigates how environmental and genetic factors combine to influence Parkinson’s risk. For this analysis, they looked at information from 829 people diagnosed with Parkinson’s and 824 people without the condition. They then combined decades of detailed pesticide application records from California with the participants’ residential and workplace address histories. This allowed them to estimate the degree of chlorpyrifos exposure based on where each person had lived or worked over time.

The pattern that emerged was striking. People with prolonged residential exposure to chlorpyrifos had more than 2.5 times the risk of developing Parkinson’s disease compared with those who had not been similarly exposed. This type of population study cannot, by itself, prove that the pesticide caused Parkinson’s. It does, however, highlight a strong association that warrants closer investigation. To move beyond correlation, the team turned to a series of laboratory experiments designed to see whether chlorpyrifos exposure could reproduce aspects of Parkinson’s in animal models and to uncover the biological mechanisms that might be involved.

In one set of experiments, the scientists exposed mice to chlorpyrifos in aerosol form for 11 weeks. They chose an inhalation route because it resembles a common way people can encounter pesticides that drift in the air. The exposed mice developed noticeable movement difficulties. When researchers examined their brains, they found a loss of dopamine producing neurons, similar to what is seen in human Parkinson’s disease. They also observed inflammation in the brain and abnormal accumulations of alpha synuclein, a protein that has become a central focus of Parkinson’s research.

Alpha synuclein normally helps nerve cells function. Under certain conditions, however, it can form abnormal clumps that are closely linked with the degeneration of neurons in Parkinson’s disease. The fact that chlorpyrifos exposure in mice led to both a loss of dopamine neurons and abnormal alpha synuclein deposits strengthens the biological link between the pesticide and key features of Parkinson’s. It supports the idea that the association seen in the human population data reflects genuine toxicity in the nervous system rather than a coincidence.

To get even closer to the mechanism, the team used zebrafish, which are a powerful model for studying how neurons develop, survive, and respond to stress. The researchers looked at what was happening inside nerve cells exposed to chlorpyrifos and found evidence of a breakdown in autophagy, a natural cellular cleanup process. Autophagy acts like an internal recycling system. Cells rely on it to remove damaged proteins and other unwanted material that, if allowed to accumulate, can impair function or trigger cell death. This system is especially important in neurons, which often need to stay healthy throughout a person’s lifetime.

When chlorpyrifos disrupted autophagy in the zebrafish models, damaged material began to build up inside neurons. That accumulation appears to contribute to neuron deterioration, including those that are critical for movement control. I found this detail striking because it connects a specific environmental exposure to a well defined cellular pathway already known to be involved in neurodegenerative disease. Importantly, the researchers did more than identify the problem. They also tested whether restoring the cleanup process could protect neurons.

In their laboratory models, enhancing autophagy or removing alpha synuclein protected nerve cells from chlorpyrifos related damage. This suggests that the pesticide’s harmful effects may depend partly on this disrupted cleanup pathway and that targeting autophagy could be a promising way to shield vulnerable brain cells. The protective effects so far have only been demonstrated in experimental systems, not in people. Even so, the findings point toward a possible therapeutic direction and underscore the idea that understanding mechanism is essential if scientists hope to design interventions.

The potential implications extend beyond chlorpyrifos itself. Although use of this pesticide has declined in the United States, many individuals were exposed in the past. Related agricultural chemicals remain in use, and researchers are interested in whether they might disrupt similar cellular processes. Identifying specific pesticides that raise Parkinson’s risk, rather than treating all pesticides as a single group, can help sharpen prevention strategies and guide public health decisions. It may also help clinicians recognize people who have had substantial exposure and may benefit from closer neurological monitoring.

Earlier identification of changes in brain function, combined with therapies that eventually might slow or prevent neurodegeneration, could change how Parkinson’s disease is managed. The new study does not yet offer such treatments, but it does provide a clearer link between a common environmental chemical and the biological signatures of Parkinson’s in the brain. As senior author Dr. Jeff Bronstein notes, the work establishes chlorpyrifos as a specific environmental risk factor, supported by evidence that disrupted autophagy can drive neurotoxicity. Future research will need to determine how these insights can be translated into safe and effective ways to protect human brain health in agricultural communities and beyond.

Read more at https://www.sciencedaily.com/releases/2026/10/261031013035.htm