Parkinson’s disease (PD) is the fastest‑growing neurological disorder in the world, and researchers increasingly believe that environmental exposure, not genetics, is the primary driver of this surge. While PD affects people everywhere, certain regions of the United States appear to have unusually high rates.
As we continue our journey across the country, our next stop brings us to a state whose striking beauty masks some equally striking environmental concerns: California. While our first chapter explored Western Pennsylvania, a region shaped by its industrial legacy and complex tapestry of pollutants, Southern California presents a different but equally compelling story. Recent research suggests that a combination of environmental toxicants, agricultural practices, industrial history, and air quality issues converge in this region. In this installment, we’ll explore what makes Southern California a national hotspot, and what its unique environmental profile can teach us about the broader fight against Parkinson’s.
Parkinson’s “Clusters” Identified in Southern California
A 2022 University of Pennsylvania study identified several U.S. Parkinson’s hotspots, including Southern California, with rates nearly 50% higher than the national average. These clusters often occur near large industrial or agricultural operations. Scientists evaluating these patterns argue that something in the environment, not random chance, must be driving the elevated risk.1
Widespread Exposure to Agricultural Pesticides
Southern California, especially areas like the Central Valley, has long been a hub for intensive agriculture. This matters because certain pesticides are strongly linked to an increased risk of PD.
Multiple studies have linked pesticides such as paraquat and rotenone to dopamine‑neuron damage, the hallmark of Parkinson’s Disease. Research by UCLA epidemiologist Dr. Beate Ritz, a leader in environmental PD science, shows that people living near agricultural pesticide application sites face a significantly higher risk of developing the disease. These toxins enter the body through inhalation of dust, drift from crop spraying, or contaminated well water.2 Animal models have repeatedly confirmed that paraquat exposure reproduces Parkinson’s‑like symptoms, strengthening the evidence that these chemicals are not just correlated with PD, they actually may cause it.
Similarly, new research in 2025 found that even a single dose of rotenone can trigger toxic changes in brain‑cell communication, initiating a cascade of neurodegeneration that resembles early Parkinson’s disease.3
Industrial Chemicals: Trichloroethylene (TCE) and Others
Beyond agriculture, Southern California also has a long industrial legacy. Many factories, dry‑cleaning operations, and manufacturing sites historically used trichloroethylene (TCE) and perchloroethylene, chemicals now believed to contribute to PD. These chemicals contaminate soil, air, and groundwater, and exposure is associated with increased PD risk in both epidemiological studies and laboratory research.4
The EPA proposed banning TCE in 2023 due to its extreme toxicity, a move reflecting growing scientific consensus around its neurological danger. Southern California’s higher density of historic industrial sites increases the likelihood that residents have been exposed at some point, sometimes without even knowing it.5
Air Pollution and Particulate Matter
Southern California is known for its smog, and many studies now link air pollution, especially fine particulate matter (PM2.5), to increased Parkinson’s risk. A national geographic analysis found that people living in areas with median levels of particulate pollution have a 56% higher risk of developing Parkinson’s compared to those in the cleanest regions. 6
Although the strongest PD hotspots for air pollution appear in regions like the Mississippi–Ohio River Valley, researchers emphasize that different regions have different toxic compositions in their air. Southern California’s pollution contains high levels of traffic emissions, industrial byproducts, and agricultural dust, a concerning combination associated with neuroinflammation and neuron death. Furthermore, a 2025 review in The Lancet Neurology highlighted air pollution as one of the three leading environmental toxicants implicated in Parkinson’s development.7
Genetic vs. Environmental Causes: Why Environment Matters More Here
Only 5–15% of Parkinson’s cases worldwide are attributed to genetics. The vast majority appear to come from environmental exposure, according to multiple international studies.
Southern California’s unique combination of:
- large‑scale pesticide use
- industrial chemical contamination
- persistent air pollution
- densely populated communities near these exposures
creates a “perfect storm” of environmental risks.
What This Means for Residents and Advocacy Efforts
If environmental factors are the main driver of PD in Southern California, the encouraging news is that Parkinson’s may be largely preventable. Reducing exposure to pesticides, cleaning contaminated sites, enforcing strict industrial chemical regulations, and improving air quality could dramatically reduce disease rates.
However, doing so requires:
- Policy change
- Public awareness
- Pressure for stronger environmental protections
- Better monitoring of chemical exposures
Researchers agree that with better prevention and policy, we could see a meaningful decline in Parkinson’s rates.
Final Thoughts
Southern California is not a hotspot for Parkinson’s Disease by accident. It’s the result of decades of exposure to pesticides, industrial chemicals, and air pollutants, many of which we now know have direct neurotoxic effects. Understanding this connection is the first step toward protecting the next generation. The more we shed light on these environmental risks, the closer we move toward prevention, advocacy, and ultimately a future with fewer Parkinson’s diagnoses.
- https://www.parkinsonsresource.org/news/articles/mystery-of-americas-parkinsons- ↩︎
- https://medschool.ucla.edu/news-article/how-are-pesticides-and-parkinsons-disease-linked ↩︎
- https://www.purdue.edu/hhs/news/2025/04/new-study-from-purdue-health-sciences-researchers-finds-early-environmental-factors-that-influence-parkinsons-disease-development/ ↩︎
- https://www.thelancet.com/journals/laneur/article/PIIS1474-4422(25)00287-X/abstract ↩︎
- https://www.parkinsonsresource.org/news/articles/mystery-of-americas-parkinsons-belt-where-chemicals-are-fueling-frightening-spike-in-brain-wasting-disease/ ↩︎
- https://www.barrowneuro.org/about/news-and-articles/press-releases/study-reveals-link-between-air-pollution-incidence-of-parkinsons/ ↩︎
- https://www.thelancet.com/journals/laneur/article/PIIS1474-4422(25)00287-X/abstract ↩︎