The invisible chemical in the air that could be raising Parkinson’s risk

• Long-term exposure to a commonly used industrial solvent may increase the risk of Parkinson's disease.
• Trichloroethylene (TCE) is often used in metal cleaning and dry cleaning. While some uses have been banned, the chemical is still employed in industry and continues to contaminate air, water, and soil across the United States.
• Researchers analyzed data for more than 1.1 million older adults using ZIP+4 codes and air pollution records to estimate long-term TCE exposure.
• Older adults living in areas with the highest TCE levels had a 10% greater risk of Parkinson's disease compared with those in the least-exposed areas.
• The findings do not confirm that TCE causes Parkinson's but strengthen evidence that environmental pollutants may play a role in the disease.

Chemical Exposure and Parkinson's Risk

Prolonged exposure to trichloroethylene (TCE), an industrial solvent, may be linked to a higher chance of developing Parkinson's disease. This conclusion comes from a major nationwide study published on October 1, 2025, in Neurology, the journal of the American Academy of Neurology.

TCE has long been used in industrial settings for metal degreasing, dry cleaning, and other purposes. Although banned for certain uses, it remains an active solvent in some industries and is known to persist in the environment. The chemical is a lasting contaminant found in U.S. air, soil, and groundwater. Researchers emphasized that the study identifies a connection, not proof of direct causation.

"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."

To conduct the analysis, researchers reviewed Medicare data from 2016 to 2018, focusing on people aged 67 and older newly diagnosed with Parkinson's disease. Each case was compared with five people of the same age and background who did not have the condition. After removing records without ZIP+4 location data, the final dataset included 221,789 individuals with Parkinson's and over 1.1 million without it.

Mapping Exposure Across the U.S.

Researchers used data from the U.S. Environmental Protection Agency to estimate outdoor concentrations of TCE in each participant's neighborhood. Air pollution levels were mapped by U.S. Census tract, a small geographic unit within each county. Exposure levels were based on where participants lived two years before their Parkinson's diagnosis.

Participants were divided into 10 exposure categories. The lowest group was exposed to between 0.005 and 0.01 micrograms per cubic meter (μg/m³) of TCE, while the highest group's exposure ranged from 0.14 to 8.66 μg/m³. After adjusting for potential confounding factors such as age, smoking, and other types of air pollution, the data revealed that individuals in the most exposed areas faced about a 10% higher risk of developing Parkinson's disease.

The team also identified several geographic "hot spots" with the highest TCE concentrations, particularly in the U.S. Rust Belt and smaller pockets scattered nationwide. They examined Parkinson's rates within 10 miles of the three largest TCE-emitting facilities in the United States as of 2002. In two of those areas, people living closer to the facilities had higher risks, and in one location, risk increased steadily the nearer residents were to the emission site.

Public Health Implications

"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," said Krzyzanowski. "This underscores the need for stronger regulations and more monitoring of industrial pollutants."

The researchers noted that the study focused on Medicare-aged adults, meaning the results may not apply to younger individuals or those with early-onset Parkinson's disease. They also pointed out that exposure estimates relied on outdoor air levels from 2002 and may not reflect a person's lifetime or indoor exposure.

The research was supported by the U.S. Department of Defense, the Kemper and Ethel Marley Foundation, Barrow Neurological Foundation, and the Moreno Family Foundation.