A new study says that exposure to the chemical solvent trichloroethylene (TCE), commonly found in soil and groundwater, increases the risk of developing Parkinson’s disease (PD). Parkinson’s is the second-most common neurodegenerative disease after Alzheimer’s disease. In the past 25 years, the number of people with the disease has almost doubled. Global estimates in 2019 showed over 8.5 million individuals with PD.
The study was conducted by researchers at the University of California, San Francisco (UCSF). They studied the medical records of nearly 85,000 Marine Corps and Navy veterans who trained at Marine Corps Base Camp Lejeune in North Carolina from 1975 to 1985.
Water contamination and TCE
They found that marines exposed to heavily contaminated water with TCE had a 70% higher risk of developing Parkinson’s disease decades later compared to corps who trained elsewhere. The Marine corps in Lejeune also had higher rates of symptoms such as erectile dysfunction and loss of smell that are early indicators of Parkinson’s. The disease causes loss of motor functions, balance, and cognitive impairment. Swallowing difficulties often lead to death from pneumonia.
At the time, wells on the base were contaminated from leaking underground storage tanks, industrial spills, and waste disposal sites. Water used on the base contained TCE levels more than 70 times the level allowed by the U.S. Environmental Protection Agency (EPA). Recruits could have ingested TCE in food or water or inhaled the highly volatile compound.
TCE is a colorless liquid that can readily be absorbed by ingestion, through the skin or by inhalation. It’s used today mainly in producing refrigerants and as a degreaser in heavy industry.
Genetic and environmental factors
The cause of PD is not known, but the general belief is that it is caused by genetic factors and exposure to environmental factors such as pesticides, solvents and air pollution over a long period of time.
The researchers compared the occurrence of Parkinson’s disease in the veterans and compared it with the rate in more than 72,000 veterans who lived at Marine Corps Base Camp Pendleton, a similar training ground in California where the TCE levels were negligible. By 2021, 279 of the Camp Lejeune veterans, or 0.33%, had developed Parkinson’s versus 151 of those at Camp Pendleton, or 0.21%. After adjusting for differences in age, sex, race, and ethnicity, the scientists found veterans from Camp Lejeune had a 70% higher rate of Parkinson’s disease than the Camp Pendleton group.
In the Camp Lejeune veterans, the researchers found higher rates of symptoms known to precede the onset of the movement disorder. The recruits had an average age of 20 at the camp, and most were around 60 at the time of analysis of record in 2021. That means that more Parkinson’s diagnoses may occur as most people develop the disease after age 60.
Earlier animal-based studies have shown that TCE acts in an area of the midbrain responsible for movement control.
The study’s lead author, UCSF epidemiologist Sam Goldman, conducted a small twin study published in 2012 showing that TCE exposure increased the risk of the disease in humans. He was prompted to undertake that study based on a published report of a cluster of Parkinson’s cases in a factory where workers were exposed to TCE, which was used as a metal degreaser.
This study was undertaken as the government found that recruits based in Camp Lejeune were reporting higher incidences of Parkinson’s later on. The U.S. government declared that any veteran who served at Camp Lejeune in the contaminated water era and had Parkinson’s disease would be presumed to have developed it because of TCE exposure at the base. Hence, Goldman undertook the study in 2017 to have a greater certainty about the causation.
The study has some weaknesses, as the government policy on Parkinson’s and access to medical care may have prompted Camp Lejeune trainees to seek care and hence, the over-representation. This is because in cases ascertained before that year, the increased risk of Parkinson’s was lower: 28%. However, the recruits were also younger and less likely to have developed the disease, for which age is the leading risk factor.
In January, EPA declared that TCE presents an “unreasonable risk of injury to human health” and said it will develop a rule regulating its use. (The chemical is also a known carcinogen.)
There are already class action lawsuits launched by veterans from the camp for health damage caused by TCE and this study will surely add meat to their claims.
