Common Chemical Linked to Parkinson’s Disease

6 min read

March 21, 2023 -- Amy Lindberg, a 63-year-old retired Navy captain, developed some disturbing symptoms 6 years ago.

“I had anxiety, depression, and cognitive issues — ‘brain fog’— and they didn’t add up for me,” she said. “I have a thyroid problem and had gone through menopause, but these didn’t seem like my standard thyroid or menopausal problems.” 

Lindberg consulted a neuropsychologist and was diagnosed with mild cognitive impairment and major depressive disorder. 

“But while he was assessing me, he asked questions I thought were strange for a psychologist to ask about. He wanted to know if I had trouble with my sense of smell. He wanted to see my arm swing.” 

Lindberg, who also had a resting tremor in her right hand, indeed had some problems with smell and a very limited arm swing. The psychologist referred her to a neurologist, who diagnosed her with Parkinson’s disease. 

The roots of Lindberg’s disease likely lie in a 4-year period when she was exposed to trichloroethylene (TCE), a common chemical that’s found in gun cleaners, cleaning products, and many other commercial products. According to a new paper by an international team of scientists, TCE may be associated with as much as a 500% increased risk for Parkinson’s disease.

When Lindberg was in her 20s, she was stationed at Camp Lejeune, a Marine base in North Carolina. “I was there between 1984 and 1988 and, unbeknownst to me, I was drinking, cooking, and swimming in tainted water.” It has since become known that the water at Camp Lejeune had been contaminated by TCE.

Lindberg is one of seven people whose stories are told in the researchers’ paper, which also contains a thorough review of animal and human studies up to the present day. Taken together, the data suggests a disturbing link between TCE exposure and the development of Parkinson’s, often decades later.

Unknown Exposure

TCE was created in a lab in 1864, with commercial production beginning in 1920, the authors wrote.

“Because of its unique properties, TCE has had countless industrial, commercial, military, and medical applications,” including refrigeration, electronics cleaning, and degreasing engine parts. Until the 1970s, it was even used to decaffeinate coffee. It has historically been used in dry cleaning, although today a similar chemical, perchloroethylene (PCE), is used instead.

The use of TCE peaked in the 1970s, when it was “ubiquitous,” in the words of the authors. About 10 million Americans worked with it or with similar chemicals. Although the numbers are lower today, a significant number of Americans still interact with this toxic chemical on a daily basis.

TCE exposure isn’t confined to those who work with it, since it also pollutes outdoor air, taints groundwater, and contaminates indoor air. It contaminates up to one-third of U.S. drinking water and is found in half of the 1,300 most toxic Superfund sites that are part of a federal cleanup program, including 15 in California’s Silicon Valley, where TCE was used to clean electronics.

Although the military has stopped using TCE, the chemical has been found on numerous military bases, including Camp Lejeune. From the 1950s to the 1980s, 1 million Marines, their families, and civilians who worked or lived at the base were exposed to drinking water levels of TCE and PCE that were up to 280 times higher than what are considered to be safe levels.

“Exposure can come via occupation or the environment and is often largely unknown at the time it occurs,” the lead author of the scientific paper, Ray Dorsey, MD, professor of neurology at the University of Rochester in New York, said in an interview.

‘Fastest-Growing Brain Disease’

Dorsey calls Parkinson’s "the world's fastest-growing brain disease.” He said genetic factors alone (which affect only about 15% of people with Parkinson’s) can’t explain the rapid rise in new diagnoses. Nor can it be explained by aging alone. 

“Certain pesticides ... are likely causes but would not explain the high prevalence of PD in urban areas, as is the case in the U.S,” he said. Rather, other factors are involved, and “TCE is likely one such factor,” Dorsey said. Yet despite widespread contamination and how often the chemical is used, there has been little investigation into the link between TCE and Parkinson’s, he said. 

To fill this gap, Dorsey and his colleagues took a deep dive into studies focusing on the potential link between TCE and Parkinson’s and presented seven cases to show the association.

They reviewed studies from as far back as 50 years ago, when the connection between TCE and Parkinson’s was first suggested. Since then, research in mice and rats has shown that TCE easily enters the brain and body tissue at high doses.

One of the human studies the authors examined compared the risk of Parkinson’s in twins, where one twin had been exposed to TCE while the other hadn’t. The researchers found a 500% increased risk of Parkinson’s in those who had been exposed.

“TCE damages the energy-producing parts of cells, the mitochondria,” Dorsey said. The nerve cells that are particularly sensitive to TCE’s toxins are those that produce dopamine, a brain chemical that’s lower in people with Parkinson’s. “This might partially explain the link.”

Public Health Options

All of the seven people whose stories were told either grew up in or spent time in a region where they were exposed to TCE, PCE, or similar chemicals, or they were exposed in their work. 

The authors admit that the role of TCE in Parkinson’s is “far from definitive.” Exposure to TCE is often combined with exposure to other toxins or with unmeasured genetic risk factors. 

But they note that Parkinson’s isn’t the only health problem linked to TCE. The chemical been connected to miscarriage, many forms of cancer, neural tube defects, and a number of other conditions. 

“Countless people have died over generations from cancer and other diseases linked to TCE, [and] Parkinson’s may be the latest,” Dorsey said. “Banning these chemicals, containing contaminated sites, and protecting homes, schools, and buildings at risk may all create a world where Parkinson’s is increasingly rare, not common.” 

For example, indoor air exposure can be improved with vapor remediation. And although efforts are under way to clean and contain contaminated sites, these efforts should be accelerated. The authors also recommend that more research be done to help understand how TCE contributes to all diseases.

Advocacy Efforts

Brian Grant is one of the people included in the paper. Once a successful NBA player who spent 12 years in the league, Grant developed symptoms of Parkinson’s at the age of 34 and retired from basketball. He was formally diagnosed 2 years later.

Grant is glad the researchers are shining a spotlight on the role of TCE and similar chemicals in Parkinson’s because he was exposed to it at the age of 3 when his father — who was then a Marine — was stationed at Camp Lejeune. His father later died of esophageal cancer, a disease known to be associated with TCE.

“I know firsthand how hard it is to live with PD,” Grant said. “I’ve seen the toll it takes on families and communities.” And Grant is worried that his children and grandchildren may also get the disease.

“So as I’ve learned from Dr. Dorsey about the research that links chemicals like TCE to PD, I feel it’s important because we can do something about it. There are things we can do to prevent future generations from getting the disease,” said Grant. 

He has created a foundation to “empower people impacted by PD to lead active and fulfilling lives.” 

Lindberg also volunteers to help veterans apply for disability and health care benefits provided by the Veterans Administration to those stationed at Camp Lejeune between 1953 and 1987. Parkinson’s is considered to be a “presumptive condition” that qualifies for these benefits based on a disability rating scale.

She also worries about the impact of the contaminated water on her children, especially since she was pregnant during her years at Camp Lejeune. Like Grant, she seeks to make the world a better place for people with Parkinson’s. 

“I’m an advocate at local, state, and national levels,” she said. “I want to improve the quality of life for people with PD and stem the tide of how fast this disease is progressing.”