WASHINGTON — The Environmental Protection Agency finalized a rule in December 2024 to phase out most uses of trichloroethylene, or TCE, a solvent that can seep into groundwater and has been increasingly linked to Parkinson’s disease. New studies are adding weight to the concern, even as legal challenges and deadline extensions complicate how quickly the federal crackdown will reduce exposures, Dec. 22, 2025.
TCE has long been used to degrease metal parts and in other industrial settings. Once released, it can migrate through soil into groundwater and, in some places, wind up in drinking water or drift into buildings as vapor.
What the new data suggest about Parkinson’s disease
A new Barrow Neurological Institute analysis compared modeled residential exposure to outdoor TCE in 2002 with diagnoses recorded among Medicare beneficiaries in 2016-2018. The study included 221,789 patients diagnosed with Parkinson’s disease and 1,132,765 people without the diagnosis and reported a positive association between higher TCE exposure and later Parkinson’s disease risk, while emphasizing that the results do not prove cause and effect.
“We identified a positive association between ambient TCE and Parkinson’s disease risk,” said Brittany Krzyzanowski, an assistant professor of neurology at Barrow and a study author. Researchers say that matters because symptoms can develop slowly, sometimes surfacing years after exposure.
For drinking water systems, the federal maximum contaminant level for trichloroethylene is 0.005 milligrams per liter, or 5 parts per billion, under national primary drinking water regulations.
Evidence has been building for years
The new findings arrive after years of concern around TCE “hot spots,” including military and industrial sites. A 2023 JAMA Neurology study reported that the risk of Parkinson’s disease was 70% higher among veterans who lived at Camp Lejeune in North Carolina during years when the base’s water systems were contaminated with TCE and other volatile organic compounds, compared with veterans stationed at Camp Pendleton in California.
A 2023 literature review in the Journal of Parkinson’s Disease traced concern back to case reports and small studies dating to the late 1960s and argued that exposure is not limited to the workplace — the chemical can pollute outdoor air, taint groundwater and migrate indoors through vapor intrusion.
University of Rochester researchers noted in a March 2023 research update that many people develop Parkinson’s disease decades after exposure, a lag that can make it difficult to tie a diagnosis to a specific contamination source.
EPA’s ban is sweeping, but key provisions are still in flux
EPA’s rule, laid out in a final regulation under the Toxic Substances Control Act, is designed to prohibit all uses of TCE, with most uses scheduled to end within a year and limited exemptions requiring workplace controls. The rule aims to reduce serious health risks linked to the chemical, but a web of court challenges has slowed and reshaped parts of the rollout.
In its latest delay notice, EPA said it is postponing certain exemption-related conditions until Feb. 17, 2026, in an extension published in the Federal Register. The agency has also moved some compliance dates for narrow uses; a separate interim final rule on compliance date extensions pushed back deadlines for TCE as a processing aid in nuclear fuel manufacturing and for certain wastewater disposal provisions.
For communities that already have TCE in drinking water, the federal ban does not remove the chemical overnight. But researchers say curbing production and releases could reduce future exposures — while cleanup of legacy contamination continues through state and federal remediation programs.
