Is Parkinson's disease man-made? Dutch researcher highlights link between pesticides, neurotoxicity

In the early 1980s, a group of young heroin users in California were suddenly left paralyzed and unable to speak after ingesting a synthetic drug tainted with MPTP, a neurotoxin that destroyed the substantia nigra, the brain region responsible for movement. Their symptoms mimicked late-stage Parkinson’s disease, which stunned doctors who had previously believed the disease developed only slowly with age. These cases revealed a sobering truth: a single chemical could trigger full-blown Parkinson’s virtually overnight.

This discovery profoundly influenced Dutch neurologist Bas Bloem, who went on to become a leading figure in Parkinson’s care and research at the Radboud University Medical Center in the Netherlands. His work is inspired by US neurologist William Langston with whom Bloem worked together, according to an article by Politico, who had first connected MPTP to Parkinson’s. Bloem became a vocal advocate for investigating the environmental roots of the disease and is now convinced that Parkinson’s is largely man-made. “A single chemical had replicated the entire disease. Parkinson’s wasn’t just bad luck. It could be caused,” Bloem says.

Although aging and genetics play a role in Parkinson’s, Bloem and other experts argue that they cannot explain the sharp global rise in cases. Parkinson’s has more than doubled worldwide in the last two decades and is projected to double again in the next 20 years. Bloem co-authored a 2024 paper asserting that Parkinson’s is “predominantly an environmental disease,” likely driven by long-term exposure to toxins like pesticides, industrial chemicals, and air pollution.

One chemical under intense scrutiny is paraquat, a herbicide chemically similar to MPTP. Though banned in the European Union since 2007 but only after Sweden took the European Commission to court for ignoring the evidence of its neurotoxicity,  paraquat continues to be produced and used in countries like the US, Australia, and across Latin America. Lawsuits in the US and Canada allege paraquat exposure led to Parkinson’s, but its manufacturer, Swiss-based and Chinese-owned company Syngenta, denies any causal link. The company cites regulatory reviews in several countries that found no definitive evidence, and insists that paraquat is safe when used correctly. Nonetheless, critics say these assessments overlook the long-term neurological damage that might not appear in short-term toxicity studies.

Hidden danger behind most commonly used herbicide

Bloem is also concerned about glyphosate, the world’s most widely used herbicide. While best known for its links to cancer — Bayer, which bought glyphosate’s original maker Monsanto, has paid over $10 billion to settle related lawsuits — some research suggests the chemical may also harm brain function indirectly, through inflammation and gut microbiome disruption. Glyphosate is pervasive, found in food, dust, water, and even rain. Though no regulator has linked it to Parkinson’s, Bloem argues this is due to outdated safety testing that focuses on acute effects, not the subtle and gradual neurological damage Parkinson’s causes.

The current regulatory framework typically examines chemicals in isolation and looks for immediate harm, rather than studying the cumulative or combined effects that might cause diseases over time. A 2020 study in Japan showed that rodents exposed to both glyphosate and MPTP suffered far more brain damage than from either chemical alone — a finding that underscores the need for better, more realistic testing.

Furthermore, Bayer and Syngenta have come under fire for failing to disclose brain toxicity studies to European authorities, despite having shared them with US regulators. Syngenta has since submitted the required studies and claimed they weren’t related to Parkinson’s. But Bloem questions whether companies profiting from these chemicals should be trusted to self-report risks to public health.

Some countries have started to acknowledge a link between pesticide exposure and Parkinson’s. France, Germany, and Italy now recognize it as a possible occupational disease, providing affected farmworkers with access to compensation. Still, Bloem argues that recognition hasn’t translated into sufficient regulatory reform.

Ultimately, he believes the world is failing to prevent a disease that is becoming increasingly common — and that the risks of continued chemical exposure are being grossly underestimated. “The chemicals we banned? Those were the obvious ones,” he says. “What we’re using now might be just as dangerous.”

By Nazrin Sadigova