In the summer of 1982, seven heroin users were admitted to a California hospital - paralyzed and mute. They were in their twenties, otherwise healthy - until a synthetic drug they had produced in makeshift laboratories trapped them inside their own bodies. Doctors quickly discovered the cause: MPTP, a neurotoxic contaminant that had destroyed a small but crucial part of the brain - the substantia nigra, which controls movement.
The patients developed symptoms of late-stage Parkinson's disease almost overnight.
These cases shocked neurologists. Until then, Parkinson's had been thought to be a disease of old age, with a slow and mysterious origin. But here was evidence that a single chemical could cause the same devastating outcome. It also turned out that MPTP was chemically similar to paraquat, a widely used herbicide that had been sprayed on farms across the United States and Europe for decades.
Although some patients partially regained mobility thanks to medication, the damage was permanent - seven of them never fully recovered.
For Dutch physician Bas Blum, this story would become a turning point. In 1989, shortly after graduating from medical school, Blum traveled to the United States to work with William Langston, the neurologist who had discovered the link between MPTP and Parkinson's disease. What he saw there fundamentally changed his understanding of the disease and its causes.
"It was like a bolt from the blue," says Blum. "A single chemical caused the entire disease. Parkinson's is not just bad luck. It can be caused."
How the disease originated
Today, 58-year-old Blum runs a globally recognized clinic and research team from his base at the Radboud University Medical Center in Nijmegen, a Dutch city near the German border. The clinic treats hundreds of patients each year, while the team conducts pioneering studies on early diagnosis and prevention.
Unlike many researchers of his stature, Blum does not stay on the sidelines. He speaks at international conferences, advises policymakers, and presents his views to both the public and the scientific community.
His work spans both care and causes - from promoting physical activity and personalized treatment, to raising awareness about potential triggers for the disease. In addition to his focus on exercise and prevention, he has become one of the most vocal critics of the environmental impact of Parkinson's disease - and what he sees as a growing failure to address the long-term effects of these factors on the human brain.
"Parkinson's is a man-made disease," he says. "And the tragedy is that we're not even trying to prevent it."
When English surgeon James Parkinson first described ‘shaking palsy’ in 1817, it was considered a medical curiosity – a rare condition affecting older men. Two centuries later, Parkinson’s disease has more than doubled globally in the past 20 years and is expected to double again in the next 20. Today, it is one of the fastest-growing neurological disorders in the world, faster than stroke and multiple sclerosis. The disease causes the progressive death of dopamine-producing neurons, gradually robbing people of their mobility, speech and eventually cognitive abilities. There is no cure.
Age and genetic predisposition play a role. But Blum and the wider neurological community argue that these two factors alone cannot explain the sharp increase in cases. In a 2024 paper with American neurologist Ray Dorsey, Blum writes that Parkinson’s is “predominantly a disease of environmental influences” – a condition shaped less by genetics and more by prolonged exposure to toxic substances such as air pollution, industrial solvents and, above all, pesticides.
Most of the patients who come through Blum's clinic are not farmers, but many live in rural areas where pesticide use is widespread. Over time, he began to notice a pattern: Parkinson's disease was more common in regions dominated by intensive agriculture.
"Parkinson's was a very rare disease until the early 20th century," says Blum. "And then, with the agricultural and chemical revolutions, and the explosion in pesticide use, rates started to rise."
Europe has taken some steps based on scientific evidence. Paraquat - a herbicide chemically similar to MPTP - was finally banned in 2007, although only after Sweden sued the European Commission for ignoring evidence of its neurotoxicity. Other pesticides known to be linked to Parkinson's disease, such as rotenone and maneb, are no longer approved.
But that's not the case everywhere. Paraquat is still produced in the UK and China, sprayed on farms in the US, New Zealand and Australia, and exported to parts of Africa and Latin America - regions where Parkinson's disease rates are now skyrocketing.
Once the world's second-best-selling herbicide - just behind glyphosate - paraquat brought huge profits to its manufacturer, Swiss-based and Chinese-owned Syngenta. But its commercial peak is long past, and the chemical now accounts for only a small portion of the company's total business. In the US, Syngenta is facing thousands of lawsuits from people who claim paraquat caused their Parkinson's disease. Similar cases have been filed in Canada.
Syngenta has consistently denied any link between paraquat and Parkinson's disease, citing regulatory reviews in the US, Australia and Japan, which reportedly found no evidence of a causal link.
The company told Politico that the comparisons with MPTP have been repeatedly disputed, citing a 2024 Australian review that concluded that paraquat does not act through the same neurotoxic mechanism. There is strong evidence, Syngenta said, that paraquat does not cause neurotoxic effects through ingestion, skin contact, or inhalation.
"Paraquat is safe when used as directed," Syngenta said.
However, for Blum, even European bans are no reason for consolation.
"The chemicals we banned? Those were the obvious ones," says Blum. "The ones we're using now may be just as dangerous. We're just not asking the right questions."
Chemicals that Europe cannot do without
Among the chemicals still in use, none has garnered more attention — or survived more court battles — than glyphosate.
It is the most widely used herbicide on the planet. Traces of it can be found on farmland, in forests, rivers, raindrops, and even in the treetops deep in European nature reserves. It is present in household dust, animal feed, and supermarket fruit and vegetables. In one American study, glyphosate was found in 80 percent of urine samples taken from the general population.
For years, glyphosate, sold under the brand name Roundup, has been at the center of an international legal and regulatory storm. In the U.S., Bayer - which acquired Monsanto, the original maker of Roundup - paid more than $10 billion to settle lawsuits linking glyphosate to non-Hodgkin lymphoma.
Glyphosate is no longer under patent protection and is now produced by numerous companies around the world. However, Bayer remains its biggest seller - with an estimated €2,6 billion in revenue from glyphosate-based products in 2024, despite increasing competition and legal pressures that are squeezing profits.
In Europe, lobbyists from the agricultural and chemical sectors are fighting hard to keep its use, warning that a ban on glyphosate would devastate agricultural production. National governments are divided. France has tried to phase it out. Germany has promised a total ban, but has never implemented it.
Despite growing concerns, gaps in safety data, and political pressure, the European Union approved glyphosate in 2023 for another 10 years of use.
Although most of the discussion about glyphosate focuses on cancer, some studies have pointed to possible links to reproductive system damage, developmental disorders, hormonal imbalances, and even childhood cancers.
To date, glyphosate has never been definitively linked to Parkinson's disease. Bayer said in a written response to Politiko that no regulatory review has ever concluded that any of its products are linked to the disease, and pointed to the US Agricultural Health Study, which followed nearly 40.000 pesticide users and found no statistically significant link between glyphosate and the disease. Bayer stressed that glyphosate is one of the most extensively studied herbicides in the world, and that no regulator has identified it as neurotoxic or carcinogenic.
However, Bloom argues that the absence of a proven link says more about how we regulate risk than about how safe the chemical actually is.
Unlike paraquat, which causes immediate oxidative damage and has been linked to Parkinson's disease in both laboratory and epidemiological studies, glyphosate's potential harms are more indirect—acting through inflammation, microbiome disruption, or mitochondrial dysfunction, all mechanisms known to contribute to the death of dopamine-producing neurons. But that's precisely why they're harder to detect with traditional toxicology tests, and easier to dismiss.
“The problem is not that we don't know anything, but that we don't measure the kind of damage that Parkinson's causes,” says Blum.
The current EU framework for evaluating pesticides, like many other regulatory systems, focuses largely on acute toxicity – short-term signs of poisoning such as seizures, sudden organ damage or death. Manufacturers provide safety data, mostly based on animal studies that track observable changes in behavior. But unlike the heroin users in California who were exposed to an unusually potent toxin, Parkinson’s disease does not manifest itself with dramatic symptoms in the short term. It creeps in as neurons gradually die, often over decades.
Regulatory tests also isolate individual chemicals and rarely examine how they interact in the real world. But a 2020 study from Japan showed how dangerous that assumption can be. When rodents were exposed to both glyphosate and MPTP — the same compound that mimicked Parkinson’s disease in heroin users in California — the combination caused far more brain cell loss than either substance alone.
"It's a nightmare," Blum says. "And we don't test for it."
Even when data exists, it doesn't always reach regulators. Internal company documents, released during court proceedings, suggest Syngenta has known for decades that paraquat can damage the brain - a claim the company denies, insisting there is no proven link.
More recently, Bayer and Syngenta have faced criticism for failing to share neurotoxicity studies with EU authorities - even though they have provided the same data to regulators in the US. In one case, Syngenta failed to report studies on the pesticide abamectin. The European Commission and the EU's food and chemicals agencies have deemed this a clear violation of the regulations.
Blum, however, sees a deeper problem. “Why would we assume that these companies are the best guardians of public health?” he asked. “They make billions off these chemicals.”
Syngenta states that none of the studies they did not share were related to Parkinson's and that they have since provided all requested studies in accordance with EU transparency rules.
Some governments are already responding to the link between Parkinson's and agriculture. France, Italy and Germany now officially recognize Parkinson's as a possible disease linked to pesticide exposure - which allows some affected agricultural workers to qualify for compensation. But even that recognition, Blum argues, has not forced the wider system to adapt.
Where science stops, politics begins
Blum's distrust is directed directly at the institutions that are supposed to protect public health - and at people like Bernhard Url, a man who has spent the last decade at the helm of one of the most important of them.
Url is the outgoing executive director of the European Food Safety Authority (EFSA), the EU's scientific body for assessing risks to food and chemicals. The agency has previously been criticized for relying on studies submitted by companies themselves. Url does not deny this, but says the process is now more transparent and scientifically rigorous.
Url, originally from Austria and a veterinarian by profession, does not dispute the essence of the criticism.
“There are areas that we are not yet considering,” he said, pointing to new scientific insights into microbiome disruption, chemical interactions, and chronic low-dose exposure. He did not explicitly mention Parkinson’s disease, but the implications were clear. “We are constantly trying to keep up,” he admitted.
Part of the problem, he said, is structural. The agency operates within a system based on predefined methods and data provided by industry. “We base our risk assessment on what we get and what the system allows us to assess,” Url said. “But the science is evolving faster than the legislation. That’s always a tension.”
EFSA also operates under constraints that do not apply to its pharmaceutical counterpart, the European Medicines Agency (EMA). “EMA distributes money to national agencies,” says Url. “We don’t do that. There is less integration, less joint working. We depend on member states voluntarily sending experts. We are not in the same league.”
Url doesn't sound defensive, but rather someone who has long struggled against institutional inertia. He described EFSA as an agency tasked with assessing a food system worth trillions, but with limited scientific resources and within a regulatory model that was never designed to address the risks of chronic diseases like Parkinson's.
"We are not getting the support we need to coordinate at a European level," he said. "Compared to the economic importance of the entire agri-food industry... it's crumbs."
But he drew a clear line on responsibility. “What is safe enough – that is not a question for us to answer,” he said. “That is a political decision.” EFSA can flag a risk, but it is up to governments to decide whether that risk is acceptable.
Blum, however, is more direct: Science can illuminate the path, but politics decides which path - and whether - to take. And in a food system shaped by powerful interests, that decision is rarely made in a vacuum.
"There are gaps," Url said, "and we have pointed them out."
But gaps in science do not always lead to action, especially when the price of precaution is perceived as a threat to economic interests.
The doctor who doesn't want to slow down
The evidence from the field is increasingly difficult to ignore. In France, one study found that rates of Parkinson’s disease are significantly higher in wine-growing regions that rely heavily on fungicides. Another study found that areas with higher use of agricultural pesticides had higher rates of Parkinson’s, suggesting a dose-response relationship. In Canada and the United States, the maps of Parkinson’s disease hotspots almost completely overlap with areas of intensive agriculture.
The Netherlands has not yet released comparable data, but Blum believes it is only a matter of time.
"If we mapped Parkinson's disease here, we would find the same patterns. We just haven't looked yet," he said.
In fact, the first signs are already emerging. The Netherlands, known for one of the highest pesticide use rates in Europe, has seen a 30 percent increase in Parkinson’s cases in the past decade—a slower rate than in some other parts of the world, but still significant, says Blum. In farming regions like the Betwee, in the lower Rhine, physiotherapists have reported pronounced local hotspots. One village near Arnhem has recorded more than a dozen cases. “I don’t know of any farmers who are deliberately doing something wrong,” says Blum. “They’re just following the rules. The problem is that the rules are wrong.”
For Blum, stopping the epidemic means changing the regulatory approach from reaction to prevention. That means mandating long-term neurotoxicity studies, testing combinations of chemicals, taking into account real-world exposures, genetic predisposition, and the type of brain damage Parkinson's causes—and, crucially, placing the burden of proving safety on manufacturers, not on scientists to prove harm.
“We don't ban parachutes until they fail,” says Blum. “But we do that with chemicals. We wait for people to get sick.” Blum is aware of the limitations of individual action and says change must come from the top of the system.
Blum has seen it before—the same pattern, only in slow motion. “Asbestos,” he says. “Lead in gasoline. Tobacco. Each time, we responded decades after the damage was already done.” The science was there. The evidence was piling up. But the decision to intervene was always delayed. “It’s not that we don’t know enough,” he adds. “It’s that the system isn’t designed to listen when the answers are unpleasant,” Blum says.
"If we don't fix this now, in 50 years we'll look back and ask, 'What on earth did we do wrong?'" he concluded.
Prepared by: A.Š., NB
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