31
Oct
Environmental Toxicants, including Pesticides, Linked to Parkinson’s Disease
(Beyond Pesticides, October 31, 2025) A review in Lancet Neurology provides a clear snapshot of the state of scientific understanding of Parkinson’s disease and how medicine and policy could be improved by shifting focus to the primary causes of the disease, namely environmental toxicants, and to emphasize prevention rather than devoting resources only to treatments and a cure. The study, led by Ray Dorsey, M.D. of the Atria Research and Global Health Institute and the University of Rochester Medical Center, focuses on three classes of environmental toxicants: pesticides, dry cleaning and degreasing chemicals, and air pollution. Because these are pollutants introduced by humans, the authors say, they should be controllable, and “Parkinson’s disease could be thus largely preventable.”
According to the review, in the last five years, new evidence has accumulated about three types of pesticides of particular concern. They are not all insecticides, which is the pesticide category most associated with neurological damage. Paraquat is a herbicide used on corn, soybeans, and cotton. Rotenone is used to kill rats and insects. Organochlorine insecticides comprise the third class. The review notes that there are many other pesticides that are neurotoxic and may have common mechanisms of action leading to Parkinson’s and other neurological diseases. The degreaser trichloroethylene (TCE) and the dry cleaning agent perchloroethylene (PCE, aka tetrachloroethylene) round out the group of bad actors.
James Parkinson, M.D., first described the disease in 1817. The knowledge that 85% of cases had no family history came in 1893; today it is estimated that only 5%-15% of people with Parkinson’s outside Africa have a genetic cause or risk factor, according to the Dorsey review.
Symptoms of Parkinson’s, such as tremors, stiffness, slow movement, and balance issues, emerged in cases of exposure to paraquat and TCE during the 1960s and to MPTP, a synthetic opioid, in the 1980s. Beginning in the late 1990s, more evidence surfaced of pesticides’ role—including rotenone and organochlorines—along with air pollution. In 2017, the Global Burden of Diseases, Injuries and Risk Factors Study identified Parkinson’s as the world’s fastest-growing neurological disease.
One of the striking aspects of these toxicants is their long chemical histories, including knowledge of their toxicities. The organochlorine DDT was first synthesized in 1874. Its usefulness as an insecticide was discovered in 1939. By the end of World War II, its toxicity to non-mosquitoes was evident; another organochlorine, dieldrin, had already been developed in the 1940s as an alternative. Even before Rachel Carson published Silent Spring in 1962, DDT was known to bioaccumulate in humans and public suspicion was mounting.
Paraquat was synthesized in 1882 and used as a dye initially. The first evidence of its human toxicity, which is severe, appeared in 1964, only two years after its commercial introduction as a pesticide. It remains legal for use in the U.S. Beyond Pesticides has consistently campaigned to ban paraquat, showing that EPA failed to meet its mandates under the Federal Insecticide, Fungicide, and Rodenticide Act and the Food Quality Protection Act. See Beyond Pesticides’ April 16, 2024, Daily News Blog for a detailed analysis of paraquat’s health hazards and regulatory status. In late 2024, California passed a bill to evaluate whether paraquat should be banned with a deadline of January 2029.
Rotenone, derived from several plants including jicama vines, has long been used by indigenous peoples to kill fish. It was isolated by a Japanese chemist in 1902 and was registered as a rodenticide and insecticide under FIFRA from 1947. EPA continues to allow its use to kill fish, but not as an insecticide.
TCE and PCE are very closely related and well-known neurotoxicants. The authors cite the heartbreaking study from 2023 of service members at Camp Lejeune in North Carolina, who were exposed to both chemicals, along with others, both occupationally and in their drinking water, through ingestion, dermal absorption, and inhalation. The cohort were service members, with an average age of 20, who were at the base for at least three months between 1975 and 1985. They were found to be at 70% higher risk of Parkinson’s than military workers at Camp Pendleton in California, which had much less pollution. Nationally, TCE contamination is now widespread: by 2000, 30% of the groundwater in the U.S. was polluted with it, and EPA estimates between 9% and 34% of drinking water sources contain some TCE.
TCE came into commercial use in the 1920s in the U.S. It has been used as a nerve pain reliever and an obstetrical anesthetic. Today it is used as a solvent in paint, ink, and adhesive formulation and as a degreaser for metal parts. EPA prohibited TCE for all uses effective January 16, 2025, but President Trump froze the action a week later, and there is a judicial stay in place. PCE became the leading dry cleaning solvent in the 1940s. It has also been used in textiles, in the manufacture of ozone-depleting CFC refrigerants, as a treatment for hookworms, and in shoe polish. EPA has set a 10-year phaseout of PCE in dry cleaning and prohibited its use by consumers.
For Parkinson’s and other neurological diseases, inhalation is a crucial route of exposure; inhaled substances—vapors, gases, and ultrafine particles—travel up the olfactory nerve in the nose to the olfactory bulb in the brain, avoiding metabolism by the liver. The olfactory bulb is a particular site of Parkinson’s pathology, and serves as a gateway to the rest of the brain.
There are other routes as well. Ultrafine particulates in air pollution can reach the brain from the lungs or digestive tract to the blood and then across the blood-brain barrier. Dr. Dorsey has proposed a connection between Parkinson’s, the gut microbiome, and the parasympathetic and enteric nervous systems. See Beyond Pesticides’ Daily News Blog of April 19, 2024, for a detailed analysis of his thesis, as well as how toxicants reach the brain and affect multiple neurological processes and structures.
Parkinson’s is a disease of industrialization. The authors note that the disease’s prevalence in Canada is five times higher than in sub-Saharan Africa, but that rapidly industrializing countries like China and India have the fastest-growing prevalence. Within less-industrialized countries, air pollution may be the primary route of toxicant exposure, as there is a strong gradient of poor air quality across the development divide. Studies in the last four years have found significant associations between PM2.5) (particulate matter) and Parkinson’s risk. The magnitude of risk is not as big as that for pesticides and dry cleaning chemicals, but the risk is very widespread because nearly everyone breathes polluted air.
The review authors also stress that while the prevalence of Parkinson’s is fairly well measured, incidence is something else. Prevalence is the current number of cases in a population in a given time period, while incidence is the number of new cases arising. In other words, we know more or less how many people have Parkinson’s, but not how many people are on the way to or newly being diagnosed with active disease. In the U.S., about a million people suffer from the disease, and almost 60,000 new cases are diagnosed annually. Prevalence could indicate increased incidence or longer survival times, so that more people are living with the disease, although a 2021 study in Neurology found that the death rate from Parkinson’s in the U.S. had more than doubled between 1999 and 2019. Thus, the relationships among incidence, prevalence, and mortality rate are still unclear. In any case, while we may have been able to increase life expectancy, we cannot yet prevent disease initiation, onset, or ultimate outcome.
Parkinson’s shares with several other neurological diseases a late-onset pattern, with many years possible between toxicant exposures and manifestation of symptoms. For example, exposures that produce Parkinson’s may occur prenatally or in early childhood. Many pesticides and solvents cross the placenta. Fat-soluble pesticides are present in breast milk. Tragically, a Marine’s son, exposed at Camp Lejeune as a three-year-old, developed Parkinson’s at age 36. The primary cohort of Camp Lejeune service members, exposed briefly in their 20s, is expected to produce many more Parkinson’s cases as the group ages into its 70s.
The Dorsey review authors stress, therefore, that more research must be conducted, preferably with biomonitoring, to detect precursor indicators that Parkinson’s is brewing, long before it becomes symptomatic.
So far, little emphasis has been placed on prevention by researchers, chemical producers, or regulators. According to the authors, nearly 60% of funding for Parkinson’s research comes from the pharmaceutical, biotechnology, and medical device sectors, which are vested in treating, not preventing, the disease. Similarly, foundations focus on finding a cure rather than prevention. Of all the research on Parkinson’s in the U.S., a mere 2% is dedicated to prevention. Further, genetic studies outnumber environmental studies by six to one, even though only a small percentage of Parkinson’s cases are genetically determined. “Cures in medicine are visible, laudable, and memorable,” the authors write. “By contrast, prevention is nearly invisible.”
It is time for the medical establishment and the federal regulatory system to acknowledge the environmental sources of Parkinson’s disease, to determine the magnitude of disease incidence increases along with the explosion of chemical exposures to humans and the biosphere, and to take immediate action to rectify the situation. The most urgent, obvious and direct way to do this is to get these toxicants out of our environment—out of golf courses, parks, schools, factories, homes, the air we breathe, and the food we eat—use only benign processes to clean our clothes, and to find acceptable substitutes for the poisonous compounds we use to keep our physical infrastructure functioning.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources:
Environmental toxicants and Parkinson’s disease: recent evidence, risks, and prevention opportunities
E Ray Dorsey et al.
The Lancet Neurology November 2025
https://pubmed.ncbi.nlm.nih.gov/41109237/
Literature review and meta-analysis of environmental toxins associated with increased risk of Parkinson’s disease
Aravindan et al.
Science of the Total Environment 2024
https://www.sciencedirect.com/science/article/pii/S0048969724029851
Literature Reviews Add to Wide Body of Science Connecting Pesticides to Parkinson’s Disease
Beyond Pesticides, April 23, 2025
https://beyondpesticides.org/dailynewsblog/2025/04/literature-reviews-add-to-wide-body-of-science-connecting-pesticides-to-parkinsons-disease/
Research Links Parkinson’s and Lewy Body Disease with Chemical Effects on Brain and Gut
Beyond Pesticides, April 19, 2024
https://beyondpesticides.org/dailynewsblog/2024/04/research-links-parkinsons-and-lewy-body-disease-with-chemical-effects-on-brain-and-gut/
California Bill Would Ban Deadly Weedkiller, Paraquat, Linked to Parkinson’s Disease in Face of EPA Inaction
Beyond Pesticides, April 16, 2024
https://beyondpesticides.org/dailynewsblog/2024/04/california-bill-would-ban-deadly-weedkiller-paraquat-linked-to-parkinsons-disease-in-face-of-epa-inaction/
Behind the Numbers Linking Pesticides to Neurological Disorders, the World’s Largest Source of Disability
Beyond Pesticides, July 29, 2025
https://beyondpesticides.org/dailynewsblog/2025/07/behind-the-numbers-linking-pesticides-to-neurological-disorders-the-worlds-largest-source-of-disability/
Golf Courses Linked to Parkinson’s Disease and Pesticide Use
Beyond Pesticides, May 22, 2025
https://beyondpesticides.org/dailynewsblog/2025/05/golf-courses-linked-to-parkinsons-disease-and-pesticide-use/
