Parkinson’s disease, the world’s fastest-growing brain condition, may be fueled by a common and widely used chemical, new research indicates.
Since the beginning of the 20th century, trichloroethylene (TCE) has been utilized to decaffeinate coffee, degrease metal, and dry clean clothing. It contaminates the Marine Corps base Camp Lejeune, fifteen toxic Superfund sites in Silicon Valley, and up to one-third of the United States’ groundwater.
TCE causes cancer, has been associated with miscarriages and congenital heart disease and has been linked to a 500% increased risk of Parkinson’s disease.
Researchers, including University of Rochester Medical Center neurologists Ray Dorsey, Ruth Schneider, and Karl Kieburtz, hypothesize that trichloroethylene may be an invisible cause of Parkinson’s disease in a recently published paper. They describe the chemical’s widespread use, the evidence linking it to Parkinson’s disease, and profile seven people, including a Navy captain, a former NBA basketball player, and a late US Senator, who developed Parkinson’s disease after either working with it or being exposed to it in the environment.
Trichloroethylene Contamination Widespread
Trichloroethylene was a widely used solvent used in various consumer, military, industrial, and medical applications, such as removing paint, correcting typos, cleaning engines, and anesthetizing patients.
Its use in the United States peaked in the 1970s, when more than 600 million pounds of the chemical were manufactured annually, or two pounds per American. Approximately ten million Americans worked with chemicals or other similar industrial solvents. While domestic use has since fallen, TCE is still used for degreasing metal and spot dry cleaning in the US.
TCE pollutes numerous sites across the country. TCE is present in half of the most toxic Environmental Protection Agency (EPA) Superfund sites.
The chemicals were used to clean electronics and computer chips at fifteen different locations in California’s Silicon Valley. TCE can be found in a variety of military bases, including Camp Lejeune in North Carolina. From the 1950s to the 1980s, a million Marines, their families, and civilians who worked or lived at the base were exposed to TCE and perchloroethylene (PCE), a close chemical cousin, at levels up to 280 times higher than what is considered safe.
Underground TCE Rivers
The link between TCE and Parkinson’s disease was first suggested in case studies more than 50 years ago. Trichloroethylene easily enters the brain and body tissue and, at high doses, damages the energy-producing parts of cells known as mitochondria, according to research in mice and rats.
In animal studies, TCE causes selective loss of dopamine-producing nerve cells, which is a hallmark of Parkinson’s disease in humans.
Individuals who have worked directly with TCE are at a higher risk of developing Parkinson’s disease. However, the authors warn that “millions more encounter the chemical unknowingly through outdoor air, contaminated groundwater, and indoor air pollution.”
The chemical can contaminate soil and groundwater, causing underground rivers, or plumes, to form and migrate over long distances.
One such plume, linked to an aerospace company on Long Island, New York, is over four miles long and two miles wide, contaminating the drinking water of thousands. Others can be found from Shanghai, China, to Newport Beach, California.
Aside from the dangers to water, volatile TCE can easily evaporate and enter people’s homes, schools, and workplaces, often undetected. This vapor intrusion is now most likely exposing millions of people who live, learn, and work near former dry cleaning, military, and industrial sites to toxic indoor air.
When radon was discovered to evaporate from soil and enter homes, increasing the risk of lung cancer, vapor intrusion was first reported in the 1980s. Millions of homes are tested for radon these days, but few for the cancer-causing TCE.
Trichloroethylene causes central nervous system depression, resulting in general anesthesia when inhaled. In fact, from the 1930s to the 1970s, trichloroethylene was administered, usually along with nitrous oxide, as an inhaled anesthetic in Europe and North America.
When TCE anesthesia was administered using CO2 absorbing systems, cranial nerve dysfunction (particularly the fifth cranial nerve) was common. Muscle relaxation was poor with TCE anesthesia sufficient for surgery. For these reasons as well as problems with hepatotoxicity, Trichloroethylene lost popularity in North America and Europe by the 1960s to more potent anesthetics such as halothane by the 1960s.
Parkinson’s TCE Case Studies
The article profiles seven people whose Parkinson’s disease may have been exacerbated by TCE.
While the evidence linking trichloroethylene exposure to Parkinson’s disease in these individuals is circumstantial, their stories highlight the difficulties in proving the chemical’s toxicity. Decades often elapsed between TCE exposure and the onset of Parkinson’s symptoms in these people.
Brian Grant, a 12-year NBA veteran who was diagnosed with Parkinson’s disease at the age of 36, is one of the case studies. Grant was most likely exposed to TCE when he was three years old and his father was stationed at Camp Lejeune as a Marine. Grant established a foundation to inspire and support people suffering from the disease.
Amy Lindberg, a young Navy captain who was similarly exposed to contaminated drinking water at Camp Lejeune, was diagnosed with Parkinson’s disease 30 years later.
Others who were exposed as a result of living near a contaminated site or working with the chemical are mentioned in the piece, including the late US Senator Johnny Isakson. He stepped down from office in 2015 after being diagnosed with Parkinson’s disease. He had served in the Georgia Air National Guard, which used TCE to degrease planes fifty years before.
Federal TCE Ban Needed Now
The authors point out that trichloroethylene has harmed workers, polluted the air we breathe (both outside and inside), and contaminated the water we drink for over a century. Global use is increasing, not decreasing.
The authors propose a series of actions to address the public health threat posed by TCE.
They point out that contaminated sites can be successfully remedied, and that vapor remediation systems similar to those used for radon can reduce indoor air exposure. However, the United States alone is home to thousands of contaminated sites, and the cleaning and containment process must be accelerated.
They advocate for more research into how trichloroethylene contributes to Parkinson’s and other diseases. TCE levels in groundwater, drinking water, soil, and outdoor and indoor air need to be monitored more closely, and this information should be shared with those who live and work near polluted areas.
Furthermore, the authors advocate for the eventual abolition of these chemicals in the United States. PCE is still widely used today in dry cleaning and TCE in vapor degreasing. Trichloroethylene has been banned in Minnesota and New York, but not by the federal government, despite findings by the EPA as recently as 2022 that the chemicals pose “an unreasonable risk to human health.”
- Dorsey, E. Ray et al. Trichloroethylene: An Invisible Cause of Parkinson’s Disease? Journal of Parkinson’s Disease, vol. 13, no. 2 (Jan. 2023)
- De Miranda BR, Greenamyre JT (2020). Trichloroethylene, a ubiquitous environmental contaminant in the risk for Parkinson’s disease. Environ Sci Process Impacts 22: , 543–554
- Stevens, W.C. and Kingston H. G. G. (1989) Inhalation Anesthesia (Chapter 11). In P. G. Barash et al. (Eds.) Clinical Anesthesia. Philadelphia, PA: Lippincott