Exposure to high levels of TCE could increase risk of Parkinson’s disease by 70%

The risk of developing Parkinson’s disease later in life could be increased by up to 70% by drinking water contaminated with the industrial solvent, trichloroethylene (TCE). The researchers said it was, to their knowledge, the first study to assess the association of Parkinson’s disease and exposure to a TCE-contaminated water supply, in a large, population-based cohort.

The study investigated whether the risk of Parkinson’s disease was raised in veterans who served at Camp Lejeune in North Carolina for at least three months between 1975 and 1985. The water supply to the base was contaminated with high levels of TCE, and several other volatile organic compounds (VOC), by leaking underground storage tanks, industrial spills, waste disposal sites and an off-base dry-cleaning business. The authors note that TCE and the related compound tetrachloroethylene are present in up to one-third of US drinking water supplies.

According to the researchers, between 1975 and 1985, the estimated monthly median TCE level in the water supply at Camp Lejeune was 366μg/l, more than 70 times the US Environmental Protection Agency (EPA) maximum contaminant level (MCL) of 5μg/l. Maximum contaminant levels were also exceeded for tetrachloroethylene and vinyl chloride during that time period.

Health data from 84,824 of these veterans was compared against the data of 73,298 veterans who had been based at a non-contaminated site. Overall, a total of 430 veterans had Parkinson’s disease; 279 from Camp Lejeune and 151 from the control group. The researchers calculated that the risk of Parkinson’s disease was 70% higher in Camp Lejeune veterans compared with the control group.

Among veterans without Parkinson’s disease, residence at Camp Lejeune was associated with a higher risk of several clinical diagnoses that are well-established early warnings for the condition, such as erectile dysfunction and anxiety.

Historically, TCE has been used in a wide range of industrial and commercial applications since the 1920s, including as a dry-cleaning solvent, an anaesthetic, and in carpet cleaners, spot removers, office products, and many other home-use products. Currently, the primary uses of TCE are in vapour degreasing and as an intermediate in the production of hydrofluorocarbon refrigerants and other chemicals.

The authors of the study said a ‘highly plausible explanation’ for the association of residence at Camp Lejeune and risk of or early signs of Parkinson’s disease was exposure to water contaminated with TCE. Although they said it was not possible to be certain that everyone who resided at Camp Lejeune was exposed to ‘biologically meaningful levels of contaminants’.

‘Finally, although TCE was the VOC present in the Camp Lejeune water supply at the highest concentrations, the water also contained high levels of [tetrachloroethylene], vinyl chloride and benzene,’ they wrote. ‘These other compounds, or mixtures of compounds, could have contributed to the associations we observed.’

Claire Bale, head of research communications and engagement at Parkinson’s UK, says the study adds ‘further weight’ to the building evidence that exposure to high levels of TCE are harmful and increases the risk of developing Parkinson’s. ‘While concerning, this research studied people who lived at Camp Lejeune and were exposed to exceptionally high levels of TCE in the 1950s–1980s,’ she says.

‘TCE is now tightly controlled by regulations in the UK due to its potentially harmful effects on human health so TCE exposure is unlikely to be a major factor in the development of Parkinson’s for the vast majority of people,’ she adds. ‘However, this research does raise a broader point about the chemicals and toxins that we all may be exposed to in our environments, such as through air pollution, and more research is needed to understand the role this exposure plays in the development of conditions like Parkinson’s.’