A chemical commonly used to dry clean clothes could be contributing to a sharp rise in the spread of Parkinson’s disease, according to a paper published on Tuesday.
Twelve scientists specializing in medical research said they found important “circumstantial” evidence linking the chemical trichloroethylene (TCE) to the doubling of global instances of Parkinson’s disease over the past 30 years. In their paper, published in the Journal of Parkinson’s Disease, the scientists called for much more research and regulation of TCE, warning that “widespread contamination and increasing industrial, commercial and military use,” pose a dire public health threat.
“TCE may be the most important cause of Parkinson’s disease in urban environments in the US,” said Ray Dorsey, a neurologist at the University of Rochester Medical Center and the lead author on the paper.
TCE is one of multiple environmental pollutants implicated in the rise of Parkinson’s disease. Research has also linked particulate air pollution and certain pesticides, including paraquat herbicide, to the disease. Head trauma and genetic factors also play a role, according to research findings.
TCE has been manufactured and sold globally since the 1920s. The chemical is used as a component in multiple products such as paint removers, cleaners, and degreasers, and has even been used to decaffeinate coffee. Prolonged exposure to the chemical is linked to certain cancers, including liver and kidney cancer.
At the height of the chemical’s production in the 1970s, the US produced over 600 million pounds of TCE, and about 10 million Americans may have worked with the chemical on a daily basis. TCE contamination is documented at many industrial and military waste sites, and is found in half of federal Superfund sites, according to the authors. Exposure to TCE occurs through inhalation of contaminated air, use of contaminated drinking water, or contact with the skin.
One of the most widespread instances of TCE contamination happened at Camp Lejeune, a US Marine Corps base in North Carolina. For more than 30 years, residents of the base were exposed to levels of TCE and a related chemical in their drinking water at levels that were up to 280 times safety standards, according to a 2010 report by Congress.
The presence of TCE and other contaminants at the site “likely increased the risk of cancers (kidney, multiple myeloma, leukemias, and others), adverse birth outcomes, and other adverse health effects of residents, according to the US Agency for Toxic Substances and Disease Registry.
Despite the established risks, global TCE use is projected to increase by 3% annually, according to the paper.
The authors said the evidence linking TCE to Parkinson’s disease is based on a handful of case studies, a small epidemiological study and numerous animal studies. One 2012 study of twin pairs found that exposure to TCE increased the risk of Parkinson’s by 500%.
“It is clear that TCE exposure is capable of causing the neurodegeneration seen in [Parkinson’s disease],” said Tim Greenamyre, a neurologist and director of the Pittsburgh Institute for Neurodegenerative Diseases who was not involved in the new paper. “Nevertheless, how big a proportion of [Parkinson’s disease] is caused by TCE remains to be determined.”
The lack of research is a huge obstacle to improving public health, according to Dorsey.
“In the entire world there are 26 studies that have been done on TCE and Parkinson’s disease,” he said. “That’s clearly not enough if we think this is one of the most important causes of Parkinson’s, which I think it is.”
If TCE is proven to cause Parkinson’s disease, actions could be taken to cut exposure and “prevent millions of people from ever developing this debilitating and deadly disease,” Dorsey said.
A call to ban TCE
In addition to more research, the paper calls for cleanup and containment of sites contaminated with TCE, and a ban on the use of the chemical.
“For more than a century, TCE has threatened workers, polluted the air we breathe, and contaminated the water we drink,” the authors write. “Most of this has been invisible, all of it is unacceptable, and none of it will stop until we act.”
In January, the Environmental Protection Agency (EPA) determined that TCE “presents an unreasonable risk of injury to human health,” but the agency has not limited the sale or use of the chemical. The EPA says it is now in the process of writing a proposed rule to take action to regulate TCE so that it no longer presents an “unreasonable risk to health.” It plans to release that rule in June.
Only two US states regulate the chemical currently. In June 2022, Minnesota banned most uses of TCE at sites already required to have an air quality permit, while New York banned most uses of the chemical with a bill passed in 2020.
“We’re letting companies get away with producing a chemical that we know causes cancer and likely contributes to the rise of Parkinson’s disease,” said Dorsey. “This is all preventable and addressable.”