In a paper out this week, scientists argue that a common industrial chemical is contributing to Parkinson’s disease. The chemical is called trichloroethylene, or TCE. And while some states have recently banned its use, TCE remains widely present throughout the U.S.
TCE is a colourless organic solvent that’s been in use for a century in various industries. It’s most often deployed as a degreasing agent in commercial or manufacturing facilities, but it’s also used as an ingredient in common household cleaning products, refrigerants, and dry-cleaning, and was even an anesthetic up through the 1970s. People working in these industries are most at risk for exposure to TCE, as are people in surrounding communities, since the chemical can contaminate soil and groundwater.
Too much acute exposure to TCE is thought to irritate the lungs and skin as well as cause lightheadedness and headaches. It’s also considered a carcinogen, with prolonged exposure known to raise the risk of kidney cancer and possibly other forms of cancers. And for more than a decade, some scientists have made the case for TCE being a cause of Parkinson’s disease, a neurodegenerative disorder that steadily destroys people’s ability to move independently and often causes dementia. About 90,000 people in the U.S. are diagnosed with Parkinson’s each year, while a million Americans are thought to be living with it, according to the Parkinson’s Foundation.
In a paper published Tuesday in the Journal of Parkinson’s Disease, many of these scientists have presented the evidence to date backing this hypothesis.
In a 2008 case study, for instance, researchers working on a clinical trial for Parkinson’s disease described finding patients with a shared long history of TCE exposure. Subsequent research has further supported this link, such as a 2012 study of twins that found an increased risk in siblings with known exposure to TCE and other suspect chemicals (twin studies are often used to untangle potential risk factors of a disease). Other studies in animals have indicated that TCE can harm the specific network of neurons implicated in Parkinson’s.
The new paper also profiles seven patients whose Parkinson’s might be linked to TCE, including former NBA player Brian Grant, who was diagnosed at the age of 36, and now-deceased U.S. Senator Johnny Isakson, who died in 2021. In these cases, the patients had a known history of living or working near sites where TCE levels were likely high, such as the military base Camp Lejeune. Throughout the 1950s to 1980s, TCE and other chemicals contaminated the drinking water at the base, almost certainly causing added cases of cancer and other illnesses, according to the Agency for Toxic Substances and Disease Registry, part of the Centres for Disease Control and Prevention.
“Millions of Americans have worked with TCE, and tens of millions have been (often unknowingly) exposed to the chemical through the water they drink and the indoor air they breathe,” author Ray Dorsey, a neurologist at the University of Rochester Medical Centre, told Gizmodo in an email. “TCE is known to cause cancer and may be fuelling the rise of the world’s fastest-growing brain disease.”
This link is still based on indirect and limited data. And not everyone is in agreement about the strength of the evidence. In its investigation of Camp Lejeune, the CDC’s ATSDR found that the evidence for TCE’s role in causing Parkinson’s currently met the standard of equipoise and above, meaning that it’s at least as likely to be true as not — one step below having sufficient evidence for a causal link. It’s also possible that TCE exposure doesn’t increase people’s risk of Parkinson’s evenly; maybe factors like our genetics make us more or less susceptible to the harm it can cause.
More research is needed to confirm if and how TCE (along with a related chemical called perchloroethylene, or PCE) could be causing Parkinson’s, Dorsey and his colleagues say. But in light of its known and possible dangers, the chemical should already be banned, they add. They also recommend that sites where TCE contamination is abundant should be contained and that people living or working in these areas should be informed of the risks and protected from the chemical (there are ways to remove it from drinking water, for instance).
Plenty others are starting to agree with the authors. New York and Minnesota have recently banned TCE from most industrial uses. And this January, the EPA reaffirmed its past judgment on TCE and determined that it “presents an unreasonable risk of injury to human health” in its current usage. So far, however, federal action on the chemical seems to be lagging, but the agency has said it’s working on new rules that would ban its use as a commercial degreaser and dry-cleaning ingredient.