Parkinson's Disease: Military Exposure - Causation, 50 Years Later

Parkinson's disease is the fastest-growing neurological disease in the world, and the VA estimates that over 100,000 Veterans are living with it. The VA presumes service connection for Parkinson's disease in limited circumstances, most notably Agent Orange exposure and service at Camp Lejeune between 1953 and 1987, where the drinking water was contaminated with TCE, PCE, Benzene & Vinyl Chloride. But the very same toxins linked to Parkinson's disease were part of everyday military work far beyond Camp Lejeune: on ships, flight lines, motor pools, and later around the burn pits of Southwest Asia. For these Veterans, there is no presumption, and a claim stands or falls on the medical evidence.  This article reviews that evidence.

Parkinson's Disease Is Mostly Not Inherited

Parkinson's disease is an incurable, slowly progressive loss of the dopamine-producing neurons of the substantia nigra, a region deep inside the brain. Misfolded protein clumps into Lewy bodies inside these cells, producing the hallmark resting tremor, muscle rigidity, slowness of movement and poor balance, and in some patients, dementia.  Inherited forms account for fewer than 20% of diagnoses. In other words, over 80% of Parkinson's disease occurs in people with no family history, which points clearly to external triggers. The environmental triggers positively identified in medical literature include farming pesticides and herbicides, Agent Orange, and occupational exposure to heavy metals and especially solvents such as TCE.

Where Veterans Were Exposed

Solvents (TCE and PCE).  Until the early 1990s, Trichloroethylene (TCE) was a component of virtually every degreasing solvent mixture used on mechanical equipment.  The most common mixture, MIL PD-680, consists primarily of TCE.  TCE-containing solvents are documented among the routine consumables aboard US Navy ships (supplies regularly used and replenished during normal operations). TCE was also a common paint thinner and paint remover.  Its sister solvent, perchloroethylene (PCE), was likewise used for degreasing, and as PCE degrades in the environment, it breaks down into TCE.  Protective equipment was generally not used, because the toxicity of these solvents was not appreciated until decades later.

Fuels and exhaust.  Fuel handlers, mechanics, flightline and flight-deck crews worked with jet fuels, aviation gasoline, kerosene and diesel, and breathed their combustion exhaust, which contains Benzene, nitrogen oxides, sulfur oxides, carbon monoxide and fine particulate matter.

Lead. Scraping and repainting ships and buildings exposed personnel to lead-based paint.

Camp Lejeune water.  TCE was by far the dominant contaminant, with monthly median levels more than 70-fold above permissible levels.

Solvents: TCE and PCE are linked with Parkinson’s

The strongest evidence is for TCE.  In a landmark 'twin study' of 99 World War II Veteran twin pairs in which only one twin developed Parkinson's disease, exposure to TCE conferred a 510% higher relative risk. Because twins share their genes and family history, this study design sets heredity aside.  PCE showed a similar trend.

A 2024 Medicare study of over 1.5 million beneficiaries, including 252,000 with Parkinson's disease, found an exposure “dose-response effect”: wherein the higher the airborne TCE level, the higher the rate of Parkinson's disease.  A “dose-response” is consistent with biologic causation, and not just an association.  Environmental TCE exposure conferred a 23% higher relative risk, and the most contaminated regions an 89% higher relative risk.

At Camp Lejeune itself, a study compared over 172,000 personnel stationed there with over 168,000 stationed at Camp Pendleton, a base without contaminated water. Parkinson's disease was diagnosed in 279 vs. 151 individuals, a 70% higher relative rate. Newer evidence extends to PCE: a 2026 nationwide analysis of Medicare beneficiaries found 14% greater odds of Parkinson's disease among those living within about 500 feet of a dry cleaner, declining with distance.  The authors remind us that PCE and TCE contamination often co-occur, since PCE degrades into TCE.

Based on a consensus interpretation of the published literature, the ATSDR lists Parkinson's disease among the 'Health effects with evidence that is equipoise and above for causation for TCE'.

Latency considerations

Latency matters too.  In the twin study, the average latency from TCE exposure to diagnosis was 38.3 years with a range of roughly 27 to 50 years.  What this means is that a Veteran exposed in the 1960s, 70s, or 80s may only be receiving a diagnosis NOW.

Fuels and Engine Exhaust

One meta-analysis pooled 13 case-control studies, encompassing over 4,400 Parkinson's patients and 7,100 controls.  Occupational exposure to fuels conferred a 36% higher relative risk for PD, and among the most heavily exposed, a 119% higher relative risk.  Once again, a dose-response was noted, confirming causation.

For exhaust, a recent study followed over 5 million people, with over 20,000 new Parkinson's diagnoses. First, note that PM2.5, PM10, NO2, and SO2 are the components of engine exhaust. The study found that higher exposure to these pollutants (found in engine exhaust) conferred a 165% higher risk for exposure to PM2.5, 213% for PM10, 74% for NO2, and 65% for SO2. 

Heavy Metals: Lead

Lead ions closely mimic calcium and are deposited in bone, where the biologic half-life of lead is around 25 years.  Bone thus keeps releasing lead into the blood for decades after the exposure has ended.  A 2019 meta-analysis pooling 66 occupational studies found that lead exposure conferred a 57% higher relative risk of Parkinson's Disease.

Competing Personal Risk Factors

As always, personal risk must be weighed against exposure risk, and for Parkinson's disease the list of personal risk factors is short.  A first-degree family history is the main one: in a population study of over 24 million people, having a sibling with Parkinson's disease conferred a 120% higher relative risk. A parent with Alzheimer's disease does not count, as the two diseases do not share genetics.  Repeated head trauma may be a trigger, and men are slightly more likely than women to develop the disease.  Smoking is not a risk factor; in fact, smoking, caffeine, and physical activity are associated with lower risk. Body weight is not a risk factor either, yet smoking and weight are among the factors incorrectly cited in some negative VA opinions as outweighing military exposures.

For those Veterans with none or just a few personal risk factors, their Parkinson's disease can fairly be considered to have been at least as likely as not caused by their military exposures. 

Three Veterans, One Pattern

The following actual cases are drawn from very recently delivered MedConnectVA Nexus Opinions (Independent Medical Opinions for Veterans).  A Navy damage-control officer (1962 to 1965, aircraft carrier and destroyer) was exposed to TCE solvents, jet fuel and exhaust, and lead paint.  His Parkinson's symptoms began in 2019, a latency of about 54 years, with no family history, no head trauma, and no civilian exposures.  An Air Force liquid fuels specialist (1984 to 1988) was exposed to fuels, solvents, and paint thinners, and was diagnosed in 2024, about 36 years later.  A sibling also has Parkinson's disease (a 120% higher risk), but his risk from exposures competed with that.  A Navy carrier crewman (1968 to 1972) was exposed to TCE, PFAS, and asbestos, and was diagnosed in 2022, a latency of about 50 years, with no personal risk factors. In each case, the VA's own Toxic Exposure Risk Activity (TERA) memo conceded the relevant exposures, and the latency was consistent with the twin study, allowing us to render a very strong Medical Nexus Opinion.

In Summary

Parkinson's disease is incurable and progressive, and in its late stages can mean loss of independence, swallowing difficulty, and needing full-time care.  The conditions presumed by the VA reach only a fraction of the Veterans whose service exposed them to TCE, PCE, fuels, exhaust, and lead.  Veteran Advocates should review the TERA memo for conceded exposures, assess the unique personal risk factors of the Veteran, and keep the long latency in mind before acquiescing to a negative opinion.  MedConnectVA can also assist by performing a medical pre-screening of your case without cost or obligation.