EPA document fuels the Parkinson’s debate: Is environmental pollution a big player?

By Lisa Marie Basile | Fact-checked by Davi Sherman
Published February 21, 2024

Key Takeaways

  • Experts say that environmental factors, including herbicides, air pollution, heavy metals, trichloroethylene, and pesticides, could cause Parkinson’s disease (PD).

  • Despite mounting evidence that these factors put people at risk for PD, the EPA recently OK'd the use of toxic paraquat-based herbicides linked to the disease. As a result, a coalition of agricultural and public health groups are suing the EPA. This represents an ongoing argument that PD is man-made.

  • Other experts say the root of the disease is multifactorial.

Many experts believe that Parkinson’s disease (PD)—a chronic, progressive neurodegenerative disorder —may be mediated by environmental factors.

Despite mounting evidence that the environment influences PD, the United States Environmental Protection Agency (EPA) doubled down on its controversial finding that paraquat-based herbicides (used to prevent weed growth in crops) are safe for use, according to a January 31 EPA document. Paraquat has previously been deemed toxic to humans. Specifically, the herbicide has been linked to PD, as reported by the Guardian last week.[][][]

A 2024 study published in the International Journal of Epidemiology found that “ambient paraquat exposure assessed at both residence and workplace was associated with PD, based on several different exposure measures.”[]

Due to these findings, a coalition of agricultural and public health groups are banding together to sue the EPA, demanding that the agency reassess its stance. “[T]he lawsuit’s plaintiffs say the agency again ignored evidence of the Parkinson's risk, including dozens of peer-reviewed studies sent to it by the Michael J Fox Foundation for Parkinson’s Research,” the Guardian reported.[] 

The controversy around paraquat represents a larger ongoing conversation about how PD may be mediated by multiple environmental factors. This discovery dates back to 1983 when parkinsonian syndrome was discovered in people intravenously exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) during illicit drug use.[][]

Ray Dorsey, MD, spoke to the National Institute of Environmental Health Sciences (NIEHS) about how air pollution, heavy metals, trichloroethylene, and pesticides—among other agents—potentially contribute to the development of PD.[] 

Research published in Toxicology in 2022 noted that the gut microbiome and viruses could also play a role in the development of PD. “[T]he evidence is strong that environmental risk factors play an important role in the etiology and pathology of PD,” the authors wrote.[]

“The last 25 years have seen great advances in our understanding of genetic causes of Parkinson's, but you don't go from six people to six million people with the disease because of genetic factors alone,” Dr. Dorsey told NIEHS. 

Man-made or multifactorial? The answer is likely both. 

Elsa Rodarte, MD, a movement disorder specialist and assistant professor in the Department of Neurology at McGovern Medical School at UTHealth Houston, tells MDLinx that she agrees with the need to “decrease trichloroethylene exposure through the reinvention of industrial methods and to prevent or stabilize some cases of Parkinson’s Disease through education.”

Dr. Rodarte also references a study that found a 70% higher risk of PD among 340,489 Camp Lejeune veterans compared with veterans stationed at another base. The key difference? is that the water at Camp Lejeune was contaminated with trichloroethylene and other volatile organic compounds.[] 

“Younger onset clusters like the Camp Lejeune [case] give us clues about environmental exposure,” Dr. Rodarte says. “Michael J. Fox and three others of the [estimated] 125-person cast of ‘Leo and Me’ filmed a movie in a basement in Vancouver, Canada, where radon—and who knows what else in the 70s—was high.” Those three other cast members also developed PD. 

On the other hand, Dr. Rodarte notes that while environmental factors play an undeniable role in PD, they’re not the only factor. “There are ancient Indian reports from 600 B.C. of bradykinesia and tremor and their response to the dopamine-containing herb Mucuna pruriens before rockets, oil pipes, and degreasers,” she says. 

Andrew Feigin, MD, Executive Director of the Fresco Institute for Parkinson’s and Movement Disorders at NYU Langone, echoes Dr. Rodarte’s sentiments. “Parkinson's disease is, as most diseases are, multifactorial,” he says. “The analogy I use is heart disease, cancer, obesity, and hypertension. For all of these, there’s not one cause. Many factors go into determining if [a patient] will develop it.”

For example, he refers to the leucine-rich repeat kinase 2 (LRRK2) and glucocerebrosidase (GBA) mutations, which represent two common genetic causes of PD, amounting to about 15% of cases. “Calling PD a man-made disorder is questionable,” Dr. Feigin says. “People have had symptoms long before plastics.”

How can clinicians get closer to understanding the cause?

Dr. Feigin says that the most significant known risks associated with developing PD are being older and male.

“Animal studies help determine causation, but it is difficult to extrapolate doses and susceptibilities to humans,” Dr. Rodarte says. “Algorithms to profile cellular/immune systems or even temporary immune circumstances that may make us prone to chemical toxicity, vaccine, and work injuries may be helpful for individuals but may come with ethical implications.”

Lowering the risk of developing PD

Dr. Rodarte says that people would benefit from better environmental education as well as aquifer and pollutant maps. “Waste management companies, like the Houston-based company that received chemical waste from the Ohio train accident, could make their activities public, so [people] know where not to have a picnic or plant a neighborhood farm,” she says. 

Beyond mitigating environmental risk, Dr. Feigin notes that “compelling evidence shows that vigorous aerobic exercise may lower PD risk. It’s not preventative, but it may lower risk.”

What this means for you

Experts suggest that Parkinson’s disease (PD) might stem from environmental influences such as herbicides, air pollution, heavy metals, trichloroethylene, and pesticides. Despite increasing evidence linking these factors to PD risk, the EPA recently approved the use of paraquat-based herbicides, known to be toxic and possibly associated with the disease.

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