Industrial Chemical TCE Linked to Increased Parkinson's Disease Risk in Major Study

A groundbreaking nationwide study has uncovered a concerning link between long-term exposure to the industrial chemical trichloroethylene (TCE) and increased risk of Parkinson's disease in older adults. Published in the October 1, 2025, issue of Neurology, the medical journal of the American Academy of Neurology, this comprehensive research examined over 1.1 million people, revealing that those living in areas with the highest outdoor TCE levels faced a 10% greater risk of developing Parkinson's compared to individuals in low-exposure regions.

Understanding Trichloroethylene (TCE)

Trichloroethylene is a chemical solvent widely used in industrial applications including metal degreasing, dry cleaning, and various manufacturing processes. Despite being banned for certain uses, TCE remains in active use as an industrial solvent and persists as an environmental contaminant across the United States. The chemical's ability to linger in air, water, and soil makes it a persistent public health concern that affects communities nationwide.

Study Methodology and Scale

Researchers conducted an extensive analysis using Medicare data to identify individuals over age 67 who were newly diagnosed with Parkinson's disease between 2016 and 2018. The study included 221,789 people with Parkinson's and over 1.1 million control subjects without the disease. Using sophisticated mapping techniques, researchers estimated TCE exposure levels based on U.S. Environmental Protection Agency data and participants' residential locations at the ZIP+4 level.

Key Findings and Risk Assessment

The research team divided participants into ten exposure groups based on estimated TCE concentrations. Individuals in the lowest exposure group experienced TCE levels between 0.005 and 0.01 micrograms per cubic meter (μg/m³), while those in the highest exposure group faced concentrations ranging from 0.14 to 8.66 μg/m³. After adjusting for confounding factors including age, smoking history, and exposure to fine particulate air pollution, the analysis revealed a clear pattern: people exposed to the highest outdoor TCE levels had a statistically significant 10% increased risk of Parkinson's disease.

Geographic Hotspots and Public Health Implications

Researchers identified specific geographic "hot spots" where outdoor TCE levels were particularly elevated, with notable concentrations in the Rust Belt region and smaller pockets across the country. The study further analyzed Parkinson's risk in proximity to the three top TCE-emitting facilities in the U.S. from 2002, finding increased risk closer to these facilities in two of the three locations. According to study author Dr. Brittany Krzyzanowski of Barrow Neurological Institute, "While the increased risk was modest, the sheer number of people exposed to TCE in the environment means the potential public health impact could be substantial."

Study Limitations and Future Directions

The research has several important limitations to consider. The study focused exclusively on Medicare-aged individuals, meaning findings may not apply to younger populations or those with early-onset Parkinson's disease. Additionally, TCE exposure estimates were based on outdoor air levels from 2002 and may not accurately reflect individual lifetime exposures or indoor contamination levels. These limitations highlight the need for continued research in this critical area of environmental health.

Conclusion and Public Health Significance

This landmark study adds to a growing body of evidence suggesting that environmental pollutants may contribute to Parkinson's disease risk. The findings underscore the importance of stronger regulations and enhanced monitoring of industrial chemicals like TCE. As researchers continue to investigate the complex relationship between environmental exposures and neurological health, this study provides crucial data for policymakers and public health officials working to protect vulnerable populations from potentially harmful chemical exposures.