Over and over studies have found links with certain toxic chemicals (some pesticides and the chemical trichloroethylene) and Parkinson's disease. Another recent study found that long-term exposure to high levels of the chemical trichloroethylene (TCE) in the outside air increases the risk of developing Parkinson's disease.
TCE is an industrial solvent used in numerous industrial (as a degreaser), consumer, military, and medical applications. For example, it is used in dry cleaning clothes, removing paint, as a degreaser, carpet cleaner, and engine cleaner. Unfortunately, since it is environmentally persistent, it lingers in the air, water (e.g., in the military base Camp Lejeune), and soil across the US.
Bottom line: Outdoor air pollution also matters, not just the chemicals you are directly exposed to (e.g., in your job). TCE is a hazardous air pollutant, so avoid living (if you can) near a TCE emitting facility (especially in Lebanon, Oregon and Corydon, IN) because the risk of developing Parkinson's disease is the highest for people living near there.
From Science Daily: The invisible chemical in the air that could be raising Parkinson’s risk
Long-term exposure to the industrial solvent trichloroethylene (TCE) outdoors may be linked to an increased risk of Parkinson's disease, according to a large nationwide study published in the October 1, 2025, issue of Neurology, the medical journal of the American Academy of Neurology.
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's disease, it only shows an association.
"In this nationwide study of older adults, long-term exposure to trichloroethylene in outdoor air was associated with a small but measurable increase in Parkinson's risk," said study author Brittany Krzyzanowski, PhD, of Barrow Neurological Institute in Phoenix. "These findings add to a growing body of evidence that environmental exposures may contribute to Parkinson's disease."
Researchers used Medicare data to identify people over age 67 newly diagnosed with Parkinson's 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's 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' 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's 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 (μg/m³), while those in the highest group had exposures ranging from 0.14 to 8.66 μg/m³.
After adjusting for other factors that could affect the risk of Parkinson's, 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's disease compared to people exposed to the lowest levels.
The researchers also identified several geographic "hot spots" 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's 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.