Environmental Culprits Linked to Parkinson's

Parkinson's (PD), is the fastest growing neurodegenerative diseases in the world (The Global Burden of Disease Studies, 2021). By 2050, studies have projected there will likely be over 25 million people worldwide living with Parkinson's unless environmental policy change is implemented, or a cure is found. Head trauma and genetic mutations have long been widely acknowledged and identified, though these factors don't explain the surge of PD diagnosis over recent years. In an attempt to pinpoint this dramatic increase, scientists have looked at potential environmental factors and have now flagged exposure to certain chemicals and how they directly relate to Parkinson's.

Researchers believe long term exposure to certain toxins can raise lifetime risk, especially for people with genetic susceptibilities. The most consistently implicated types of exposure are:

Pesticides and Herbicides. Numerous research studies link the agricultural chemicals paraquat, rotenone and some oraganochlorines with higher PD risk. (ScienceDirect, by P Sharma 2024)

Industrial Solvents. A growing body of case studies, animal experiments and population research ties TCE (trichloroethylene) - a solvent used historically in such things as dry-cleaning, metal degreasing, carpet cleaning and early (1970's) attempts at decaffeinating coffee (yuck) and as an inhaled anesthetic (banned in 1977) to Parkinson's.( National Library of Medicine, Trichloroethylene: An Invisiable Cause of Parkinson's Disease? E.Ray Dorsey, Maryam Zafar & others 2023), (Science Adviser, Widely Used Chemical strongly linked to Parkinson's disease, Meredith Wadman 2023)

Air Pollution and Particulate Matter. Traffic related pollution and fine particulates can promote oxidative stress and inflamation in the brain; several recent analyses find associations between air pollution exposure and increased PD incidence. I have been advocating for years at the municiple level in Toronto for stricter enforcement of the idling bi-law, especially around day cares and schools. If there's one thing we can do on a personal level, it's to choose public transit and biking whenever possible, and if we need to drive, turn off engines when not traveling. (National Library of Medicine, Environmental Risk Factors for Parkinson's, by KA Brolin, 2024)

Metals and Industrial Contaminants. Manganese, lead and other metals have been implicated in some studies, especially occupational exposures, though findings vary by metal and exposure level (National Library of Medicine, Environmental Risk Factors for Parkinson's Disease: A Critical Review and Policy Implications, Kajsa Atterling Brolin, 2024)

Important Nuance: strength of evidence varies. For some chemicals like paraquat and TCE the data is strong enough for serious concern and regulatory consideration; for others the evidence is more mixed

I'd like to break down and delve in to two of the main culprits researchers have strongly linked to the increased Parkinson's diagnosis over the past 30 years- Paraquat, and TCE and how they affect the area of the midbrain responsible for movement signals, motor learning, executive functions, emotions and reward based behaviours.

What is Paraquat?

Paraquat (paraquat dichloride) is a potent herbicide used to kill unwanted plants. It's fast acting, non-selective, and has been widely used in agriculture worldwide for decades. Besides being a herbicide, chemically it's a redox-active compound that generates reactive oxygen species in living tissue (Wikipedia)

How might paraquat be linked to Parkinson's? Research implicates paraquat in PD risk through two main lines of evidence:

1. Epidemiology ( human studies): Multiple epidemiological studies have found that people with long term or occupational exposure to paraquat have higher rates of Parkinson's disease compared with unexposed populations. These studies are the main reason paraquat is on scientists radar. ( ScienceDirect, Paraquat as a cause of Parkinson's Disease, by P Sharma 2024)

2. Biological Plausibility (lab studies) : In cells and animal models, paraquat promotes oxidative stress and mitochondrial dysfunction -mechanisms that also underlie dopaminergic neuron loss seen in Parkinson's. (ScienceDirect, Paraquat as a cause of Parkinson's Disease, P Sharma 2024)

Many countries, like Canada in 2022, have dicontinued the manufacturing and distribution of paraquat,while others including the U.S. have maintained conditional approvals alongside stricter use rules. In 2024-2025 reulatory agencies and courts in several places were activily reassessing paraquat's restictions amid lawsuits and new reviews. This is an ongoing policy issue in the U.S. (Science Adviser, EPA will soon weigh in on weed killer that may cause Parkinson's disease, Meredith Wadman, 2025), ( Parkinson Canada, 2023)

What is TCE (trichloroethylene)?

TCE is a solvent used historically in dry cleaning, and metal degreasing. It is common in soil and groundwater because of its historic long time use and detectible in many foods, drinking water, breast milk, blood and urine. 'It is a colourless liquid that readily crosses biological membranes. It turns to vapor quickly and can be absorbed by ingestion, through skin or by inhalation. It's used today mainly in producing refidgerants and as a degreaser in heavy industry.' (ScienceAdviser, Widely used chemical strongly linked to Parkinson's Disease,Meredith Wadman 2024)

A study, covered in the above cited article, published in 2024, in Jama Neurology, examined the medical records of thousands of U.S. Marines and Navy vets who trained at marine Corps Base Camp Lejeune from 1975 to 1985 who were exposed to extreme doses of TCE during their time there.

Both TCE and Paraquat act in an area of the midbrain, called the basal ganglia, which are primarily involved in motor control. They inhibit complex 1, 'the leading enzyme in a chain of reactions that convert food to energy in mitochondria...the dopamine generating neurons in the midbrain's substantia nigra are destroyed, as happens in Parkinson's disease.' (ibid)

Practical Steps to Reduce Exposure

1. Limit pesticide/herbicide use at home. If you must use chemical products, read labels and follow safety directions. Avoid routine braodcast spraying.

2. Avoid storing or using industrial solvents at home. If you must use them, work outdoors in well ventilated areas wearing appropriate PPE. Dispose of solvents at approved hazardous waste sites.

3. Be mindful of occupational exposures. If you work in agriculture, landscaping, dry-cleaning or manufacturing, talk to your employer about safer alternatives and protective measures. Use respirators and gloves when necessary.

4. Test if you suspect groundwater/ soil contamination. Old industrial sites, dry cleaners and agricultural lands can contaminate local water and soil. Local public health can advise on testing.

5. Advocate for safer policies . Community level limits on particularly hazardous chemicals and safer agricultural practices reduce population risk. I feel this is the strongest action we can all take, as the more we can implement strong regulations around harmful chemical use, the better we can protect ourselves, our family, and community.

   
   

   *Last Spring, Jean Quintero, the community outreach coordinator for the organization DrugWatch-based in Florida, reached out to me to ask if I would share their guide about the links between paraquat and Parkinson's. I'd like to thank Jean for planting the seed for this blog post as well as the important work that DrugWatch and similar organizations do to help educate and protect us against exposure to paraquat and similar toxic chemicals.

   Here's the link to their page on paraquat: https://www.drugwatch.com/paraquat/