Link Between Outdoor Trichloroethylene Exposure and Parkinson's Disease Risk Identified

Recent research indicates that exposure to the industrial solvent trichloroethylene (TCE) in outdoor air may be associated with an increased risk of developing Parkinson's disease. This finding emerges from a comprehensive nationwide study published in the journal Neurology.

TCE is commonly utilized in applications such as metal degreasing and dry cleaning. Although its use has been restricted in some areas, TCE continues to be employed as an industrial solvent and remains an environmental concern, contaminating air, water, and soil across the United States. It is important to note that this study establishes a correlation between TCE exposure and Parkinson's disease but does not confirm causation.

According to study author Brittany Krzyzanowski, the research reveals that long-term outdoor exposure to TCE correlates with a slight, yet significant, increase in Parkinson's disease risk among older adults. This adds to the growing body of evidence suggesting that environmental factors may play a role in the development of the disease.

The research team utilized Medicare data to identify over 221,000 individuals aged 67 and older who were newly diagnosed with Parkinson's disease between 2016 and 2018. Each diagnosed individual was compared to five others without the disease. After excluding those without complete residential information, the study ultimately encompassed 221,789 Parkinson's patients and over 1.1 million control participants.

To assess exposure levels, researchers mapped TCE concentrations in outdoor air based on U.S. Environmental Protection Agency data and participants' residential ZIP+4 codes. The estimated air levels were derived from U.S. Census tract data, and exposure was calculated based on neighborhood air quality two years prior to diagnosis.

Participants were categorized into ten groups based on their estimated exposure levels. Individuals in the lowest exposure group experienced TCE levels between 0.005 and 0.01 micrograms per cubic meter (ug/m³), while those in the highest group were exposed to levels ranging from 0.14 to 8.66 ug/m³. After adjusting for various factors that could influence Parkinson's risk, including age, smoking history, and exposure to fine particulate matter, the researchers determined that individuals exposed to the highest levels of outdoor TCE had a 10% elevated risk of developing Parkinson's disease compared to those in the lowest exposure category.

The study also identified geographic areas predominantly affected by high TCE levels, particularly in the Rust Belt region and other pockets across the country. An analysis of Parkinson's disease risk in proximity to the three primary TCE-emitting facilities in the U.S. revealed that risk was notably higher for individuals living closer to these sites, with a clear trend of increasing risk as proximity decreased.

Despite the modest increase in risk identified, researchers emphasize the potential public health implications given the substantial number of individuals exposed to TCE in the environment. This underscores the urgent need for more stringent regulations and enhanced monitoring of industrial pollutants.

It is essential to acknowledge the study's limitations, which include its focus solely on individuals enrolled in Medicare. Consequently, the findings may not generalize to younger populations or those with early-onset Parkinson's disease. Additionally, the estimates of TCE exposure were based on outdoor air concentrations from 2002, which may not accurately represent individual lifetime exposure or indoor air quality.