May 15, 2023

expert reaction to study of veterans from a Marine Corps Base Camp exposed to trichloroethylene and risk of Parkinson’s Disease

A study published in JAMA Neurology looks at risk of Parkinson’s disease among service members at Marine Corps Base Camp Lejeune.

Dr Chris Morris, Senior Lecturer, Translational and Clinical Research Institute, Newcastle University, said:

“Many studies have hinted at the possibility of an environmental cause for Parkinson’s and this study has tried to identify if one particular chemical, trichloroethylene, might be the culprit. Trichloroethylene has many different industrial applications in producing other chemicals and removing oil and grease from engines, and at one time was used in dry cleaning. Studies also seem to show brain changes that look like Parkinson’s in laboratory animals after exposure to high levels of trichloroethylene. 

“In this large new study of former US military personnel, there are slightly more cases of Parkinson’s in veterans exposed to trichloroethylene than in a group of veterans who weren’t exposed. This might at first sight suggest that trichloroethylene could have contributed to some of the veterans developing Parkinson’s. However, even though the study is large, over 300,000 people, there are only around 400 people with Parkinson’s. This is very similar to what you would find normally given the age of the people involved. This could indicate that the finding might simply be a chance event and so we need to be cautious in implying that trichloroethylene could be a contributor to Parkinson’s. Much larger and more extensive studies will be needed to provide definite proof.”

Prof Alastair Noyce, Professor of Neurology and Neuroepidemiology, QMUL, said:

“This is first large-scale, well-conducted, prospective, observational study into the association between trichloroethylene (TCE) and Parkinson’s disease (PD). The results suggest a 70% increase in the risk of PD in veterans who were stationed at Camp Lejeune in North Carolina between 1975 – 1985, which coincided with contamination of the water supply with TCE and other volatile compounds. Whilst this provides important evidence to support further research into the link between TCE and PD, it is noted that the strength of association weakened substantially when restricted to cases of PD that were ascertained before 2017. This is notable because 2017 was the year that news of the contamination and potential risks to health were released. Hence knowledge of the contamination may partly explain the observed association.

“Evidence from some sources suggests that the global burden of PD may be increasing and determinants of that apparent increase may come from environmental exposures or better ascertainment of cases. Either way, research into the links between TCE and other environmental toxins for PD and neurodegenerative diseases should be accelerated and preventive measures enacted through policy change.”

Dr Natasha Fothergill-Misbah, Research Associate on Transforming Parkinson’s Care in Africa NIHR grant, Newcastle University, said:

“Trichloroethylene (TCE) is a widespread solvent, developed in the 1920s, with industrial, commercial, military and medical applications, including cleaning electronics, degreasing engines, as a refrigerant, and in dry cleaning clothes. TCE was banned in the EU in the 2010s. A key action for member states in the first ever World Health Organization Technical Brief on Parkinson’s Disease published in 2022 is to ban trichloroethylene.

“The severity of TCE and its association with the development Parkinson’s Disease has recently gained traction, despite clinical studies linking TCE to Parkinson’s dating back to the 1960s. Existing evidence all points to a positive association between exposure and disease development, although more data are needed. We know that PD is largely a ‘man-made disease’, meaning that exposures to pesticides, pollutants and chemicals, for example, are largely thought to play a role in increasing risk. Genetic risk to PD only accounts for a minority of cases.

“This high quality, cohort study provides the first population-based evidence to support the hypothesis that TCE can cause PD, adding to the well-documented evidence that TCE is also carcinogenic. Although it is not possible to determine actual exposure, the significance of the association, considering confounders, provides a very plausible explanation for this increased risk, although it is certainly not the only risk factor for PD. More data are needed on the link between environmental risk factors and the development of PD. Prevalence of PD in the UK increased by 22% between 1990 and 2016. These findings have real world implications for identifying risk factors for PD and preventing exposure, thereby reducing risk of disease.”

‘Risk of Parkinson Disease Among Service Members at Marine Corps Base Camp Lejeune’ by Samuel M. Goldman, et al. was published in JAMA Neurology at 16:00 UK time on Monday 15^th May.

DOI: 10.1001/jamaneurol.2023.1168

Declared interests

Dr Chris Morris: “No conflicts of interest.”

Prof Alastair Noyce: “Chair of the International Parkinson and Movement Disorders Society Epidemiology Study Group.”

Dr Natasha Fothergill-Misbah: “I am currently working on a NIHR funded Global Health Research Group on ‘Transforming Parkinson’s Care in Africa’.

I consult for the WHO Brain Health Unit and worked on the development of the Technical Brief (https://www.who.int/publications/i/item/9789240050983)”