DRY CLEANING CHEMICAL
Barrow study: Ambient TCE exposure suggests link to Parkinson’s disease risk nationwide
(PHOENIX – Oct. 1, 2025) – A pioneering study by researchers at Barrow Neurological Institute at Dignity Health St. Joseph’s Hospital and Medical Center suggests a potential link between ambient trichloroethylene (TCE) and Parkinson’s disease nationwide.
The study, published October 1 in Neurology®, the medical journal of the American Academy of Neurology, also found a potentially greater risk of Parkinson’s disease in individuals who live near certain facilities that emit TCE compared to those whose homes are farther away.
“Ambient (outdoor) TCE concentrations are highest in the Rust Belt region of the U.S. and several smaller areas throughout the nation,” says Dr. Brittany Krzyzanowski, PhD, assistant professor of neurology at Barrow. “We identified a positive association between ambient TCE and Parkinson’s disease risk, suggesting that TCE may contribute to Parkinson’s disease.”
TCE is a chlorinated solvent used in a wide variety of industrial processes and products. In the 1920s, TCE was commonly used as a dry cleaning and degreasing agent and could be found in many household cleaning products. In the 1970s, the U.S. Food and Drug Administration banned the use of TCE as an inhaled anesthetic. Nevertheless, TCE is still used as a degreasing agent and for other purposes in a wide variety of settings, including metal and textile manufacturing.
Previous studies have associated TCE exposure to Parkinson’s disease, and have found that when inhaled or ingested, TCE readily crosses the blood brain barrier and causes dopaminergic neurodegeneration.
This study was one of the first to identify a national association between ambient TCE and Parkinson’s disease risk. Researchers investigated the association between Parkinson’s disease in 221,789 patients and 1,132,765 non-cases from the U.S. Medicare population in 2016-2018 and charted their residential exposure to ambient TCE in 2002.
To better understand the effect of ambient TCE at a local level, researchers supplemented their nationwide analysis with an exploratory study of the local patterns of Parkinson’s disease risk around the top ambient TCE-emitting facilities in 2002.
“We encourage community members to be aware of this study as well as previous studies linking TCE exposure to Parkinson’s disease risk and certain kinds of cancers,” says Dr. Krzyzanowski. “It's important to note that our study was observational and did not draw causal conclusions.”
The Barrow study was supported by the American Academy of Neurology, Kemper and Ethel Marley Foundation, Barrow Neurological Foundation, and a gift from the Moreno Family Foundation.
— ### —
About Barrow Neurological Institute
Barrow Neurological Institute, at Dignity Health St. Joseph's Hospital and Medical Center in Phoenix, is an international leader in treatment, research and education relating to brain and spinal diseases, conditions, and injuries. The Institute is one of the busiest centers for neurology and neurosurgery in the United States. Each year, more than 73,000 patients are treated at Barrow with more than 6,000 neurosurgeries performed at the Institute. Because of its high volume, Barrow clinicians are familiar with the rarest and most challenging neurological conditions and are often sought by patients from around the world for life-saving medical care. About Barrow Neurological Institute.
To learn more about Barrow, please follow us on Facebook, Instagram, LinkedIn and X.
Journal
Neurology
Method of Research
Observational study
Subject of Research
People
Article Title
Ambient Trichloroethylene Exposure and Parkinson Disease Risk in Medicare Beneficiaries
Article Publication Date
1-Oct-2025
Outdoor air exposure to chemical may raise risk of Parkinson’s disease
American Academy of Neurology
Highlights:
- Long-term exposure to a common industrial chemical may be linked to a higher risk of Parkinson’s disease.
- 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.
- Researchers estimated long-term TCE exposure for more than 1.1 million older adults by using ZIP+4 codes and air pollution data.
- Older adults living in areas with the highest TCE levels in outdoor air had a 10% higher risk of Parkinson’s than those in areas with the lowest levels.
- The study does not prove TCE causes Parkinson’s, but it adds to growing evidence that environmental pollutants may contribute to risk.
MINNEAPOLIS – 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.
“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.”
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’s 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 BrainandLife.org, the American Academy of Neurology. This resource also offers a magazine, podcast, and books that connect patients, caregivers and anyone interested in brain health with the most trusted information, straight from the world’s leading experts in brain health. Follow Brain & Life® on Facebook, X, and Instagram.
The American Academy of Neurology is the leading voice in brain health. As the world’s largest association of neurologists and neuroscience professionals with more than 40,000 members, the AAN provides access to the latest news, science and research affecting neurology for patients, caregivers, physicians and professionals alike. The AAN’s mission is to enhance member career fulfillment and promote brain health for all. A neurologist is a doctor who specializes in the diagnosis, care and treatment of brain, spinal cord and nervous system diseases such as Alzheimer's disease, stroke, concussion, epilepsy, Parkinson's disease, multiple sclerosis, headache and migraine.
Explore the latest in neurological disease and brain health, from the minds at the AAN at AAN.com or find us on Facebook, X, Instagram, LinkedIn, and YouTube.
