EMBARGOED FOR RELEASE UNTIL 4 PM ET, October 01, 2025
Outdoor air exposure to chemical may raise risk of Parkinson鈥檚 disease
Highlights: 鈥 Long-term exposure to a common industrial chemical may be linked to a higher risk of Parkinson鈥檚 disease. 鈥 Trichloroethylene (TCE) is a chemical used in metal degreasing and dry cleaning. Even though it has been banned for some uses, it remains in use today as an industrial solvent and lingers in air, soil and water across the U.S. 鈥 Researchers estimated long-term TCE exposure for more than 1.1 million older adults by using ZIP+4 codes and air pollution data. 鈥 Older adults living in areas with the highest TCE levels in outdoor air had a 10% higher risk of Parkinson鈥檚 than those in areas with the lowest levels. 鈥 The study does not prove TCE causes Parkinson鈥檚, but it adds to growing evidence that environmental pollutants may contribute to risk. MINNEAPOLIS鈥 Long-term exposure to the industrial solvent trichloroethylene (TCE) outdoors may be linked to an increased risk of Parkinson鈥檚 disease, according to a large nationwide study published in the October 1, 2025, issue of , the medical journal of the 好色先生. Trichloroethylene is a chemical used in metal degreasing, dry cleaning and other industrial applications. Although TCE has been banned for certain uses, it remains in use today as an industrial solvent and is a persistent environmental pollutant in air, water and soil across the United States. The study does not prove that TCE exposure causes Parkinson鈥檚 disease, it only shows an association. 鈥淚n this nationwide study of older adults, long-term exposure to trichloroethylene in outdoor air was associated with a small but measurable increase in Parkinson鈥檚 risk,鈥 said study author Brittany Krzyzanowski, PhD, of Barrow Neurological Institute in Phoenix. 鈥淭hese findings add to a growing body of evidence that environmental exposures may contribute to Parkinson鈥檚 disease.鈥 Researchers used Medicare data to identify people over age 67 newly diagnosed with Parkinson鈥檚 between 2016 and 2018. Each person was compared with five people who did not have the disease. After removing people without home ZIP+4 information, the study included 221,789 people with Parkinson鈥檚 and over 1.1 million people without the disease. They mapped exposure to outdoor TCE concentrations using U.S. Environmental Protection Agency data and participants鈥 residential neighborhood based on their ZIP +4 location. Air levels of TCE were estimated by U.S. Census tract, a small area within a county. Each participant鈥檚 exposure was based on their neighborhood two years prior to diagnosis. Researchers divided participants into 10 groups based on their estimated TCE exposure. Those in the lowest exposure group experienced levels between 0.005 and 0.01 micrograms per cubic meter (碌g/m鲁), while those in the highest group had exposures ranging from 0.14 to 8.66 碌g/m鲁. After adjusting for other factors that could affect the risk of Parkinson鈥檚, including age, smoking history and exposure to fine particulate air pollution, researchers found people exposed to the highest outdoor TCE levels had a 10% increased risk of Parkinson鈥檚 disease compared to people exposed to the lowest levels. The researchers also identified several geographic 鈥渉ot spots鈥 where outdoor TCE levels were highest, particularly in the Rust Belt region of the U.S. and smaller pockets across the country. They then analyzed Parkinson鈥檚 risk in the 10 miles surrounding the three top TCE-emitting facilities in the U.S. from 2002. For two of the areas, risk was higher closer to the facilities, and at one of those sites, there was a clear increasing incremental risk the closer people lived to the facility. 鈥淲hile 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,鈥 said Krzyzanowski. 鈥淭his underscores the need for stronger regulations and more monitoring of industrial pollutants.鈥 A limitation of the study is that it focused only on Medicare-aged individuals, so findings may not apply to younger people or those with early-onset Parkinson鈥檚 disease. In addition, TCE exposure estimates were based on outdoor air levels in 2002 and may not reflect individual lifetime or indoor exposures. The study was supported by the U.S. Department of Defense, the Kemper and Ethel Marley Foundation, Barrow Neurological Foundation and the Moreno Family Foundation. Discover more about brain health at , from the 好色先生. This resource offers a website, podcast, and books that connect patients, caregivers and anyone interested in brain health with the most trusted information, straight from the world鈥檚 leading experts in brain health. Follow Brain & Life庐 on , and .