Why is the United States allowing a controversial weedkiller banned worldwide?

When U.S. regulators released a 2019 assessment of paraquat, a widely used agricultural chemical, they determined that while several scientific studies linked the chemical to Parkinson’s disease, that work was surpassed by other studies that didn’t. haven’t found such links.


The Environmental Protection Agency (EPA) reiterated its assessment in a 2021 report, determining that by weighing all the risks and benefits, US farmers could continue to apply the weedkiller to millions of US acres to help production. soybeans, corn, cotton and a range of other crops.

This is in stark contrast to the EU, where it is banned. It is also banned in the UK, where it is made; Switzerland, where its manufacturer, Sygnenta, is based; and China, headquarters of Syngenta’s parent company.

A growing chorus of farmworker, health and environmental advocacy groups in the United States are demanding this change. They argue that research by independent scientists provides ample evidence of paraquat’s ability to cause Parkinson’s disease and other health hazards, and the EPA wrongly dismisses this body of research.

Last week, the Guardian and New Lede reported that internal company documents suggested Syngenta had feared a link to Parkinson’s disease for decades. He sought both to refute the evidence with studies written by his own scientists and to influence the composition of influential EPA groups that advise on pesticide regulation.

Syngenta cites the EPA’s assessment of paraquat science in defense of the pesticide, and says the scientific research “does not support” a causal relationship between the chemical and disease. On a paraquat informational website run by Syngenta, the company highlights several studies that it says also support this position, many of which were conducted by company scientists or by outside scientists who have received corporate funding for their work.

“Recent extensive reviews by the most advanced, science-based regulatory authorities, including the United States and Australia, continue to support the view that paraquat is safe,” Syngenta said in a statement. communicated to the Guardian.

The company is facing calls in the United States for a paraquat ban, as well as more than 2,000 lawsuits from people claiming to have developed Parkinson’s disease as a result of their exposure to paraquat.

More than 50 groups have called on the United States to follow the lead of dozens of other countries in banning paraquat. The Michael J Fox Foundation for Parkinson’s Research submitted a petition to the EPA with 107,000 signatories calling for a ban. The foundation cited a study that found people exposed to paraquat as teenagers or young adults had a 200 to 600 percent increased risk of Parkinson’s disease, depending on overall exposure.

In a 2022 court filing, a contingent of eight such organizations accused the EPA of violating its own risk assessment practices to dismiss what research shows about the link between paraquat and Parkinson’s disease. They told the court there is a “substantial body of evidence” for paraquat’s ability to cause Parkinson’s disease through “chronic low-dose” exposures, as well as links to other health hazards.

Study debate

Parkinson’s disease is an incurable, progressive disorder of the nervous system that severely limits a person’s ability to control their movements. It can cause tremors, loss of balance and often ends up leaving victims bedridden and/or in a wheelchair. Symptoms of Parkinson’s disease develop when dopamine-producing neurons in the brain degenerate.

Scientists studying Parkinson’s disease say research shows that genetics plays only a small role in causation and the majority of cases are believed to be triggered by environmental exposures. Along with exposure to paraquat and other pesticides, inhalation of small toxin particles in polluted air is also considered a possible cause of the disease. Farmers and farm workers who use pesticides are particularly at risk of the disease.


Some of the most debated scientific research regarding paraquat and Parkinson’s disease are studies conducted as part of the federally funded US Agricultural Health Study (AHS). The AHS began in 1993 as a research project examining the effects of pesticides on the health of farmers and other pesticide applicators. More than 89,000 farmers and their spouses from Iowa and North Carolina participated.

In 2011, AHS researchers reported that study participants who used paraquat or another pesticide called rotenone were more than twice as likely to develop Parkinson’s disease as people who did not use the drugs. chemical products.

But in a 2020 update, the AHS researchers said the 2011 paraquat findings had not been reviewed. The EPA says the study supports its finding of insufficient evidence linking paraquat to Parkinson’s disease, saying the updated study “did not report any association” between paraquat exposure and Parkinson’s disease. . And in a statement to the Guardian, Syngenta called the 2020 work “the most comprehensive study of pesticide use and Parkinson’s disease to date”.

Still, critics say the updated study suffered from several flaws, including the fact that there was a significant drop in follow-up of study participants. And they point to the fact that even the 2020 AHS researchers acknowledged in their published paper that there were “several limitations” to the study.

And despite Syngenta’s characterization, the AHS researchers said in their paper that with respect to paraquat, “prior animal and human studies offer compelling evidence of a potential link” to Parkinson’s disease. They said they could not rule out the possibility of an association between paraquat and Parkinson’s disease.

Three prominent scientists also said the EPA should give the 2020 AHS study no more weight than the many other studies done over the years.

In a court filing challenging the EPA’s assessment of paraquat, the three scientists – including Beate Ritz, co-director of UCLA’s Center for Genetic and Environmental Studies of Parkinson’s Disease – said many studies involved the paraquat as a cause of Parkinson’s disease.

Ritz has also been retained as an expert witness for plaintiffs in the litigation against Synenta, and has written a report detailing the flaws she specifically sees in the 2020 AHS study.

The scientists said the EPA reviewed 26 epidemiological studies in its assessment of paraquat and Parkinson’s disease and all but two found positive associations between the pesticide and the disease. Still, the EPA downgraded most of those studies, focusing on those that didn’t find an association, the scientists said. The agency also wrongly dismissed animal studies that found an association, they wrote.

“The EPA ignored many important epidemiological and animal studies for reasons that were not sufficiently science-based,” the scientists wrote. “Multiple lines of converging scientific evidence, published in peer-reviewed journals for many years, link paraquat to Parkinson’s disease.”

Allegations of “rigged system”

Critics accuse the EPA of being too comfortable with the pesticide industry and biasing its decisions in favor of companies selling pesticides. Several EPA scientists have come forward in the past year, publicly alleging that EPA management routinely pressures EPA scientists to change risk assessments of chemicals in ways that minimize harm. damage that chemicals could cause. EPA scientists have provided emails, text messages and other documents to Congress that the legal group representing them say demonstrates a “rigged system.” The EPA Inspector General’s Office investigates complaints.

Scientists complained, among other things, that key executives moved back and forth between industry jobs and positions at the EPA. An example is seen in the agency’s recent review of paraquat.

Records show that one of the EPA officials who signed off on the EPA’s paraquat assessment in 2019 had come to the EPA from an industry position. Biologist Kristin Rickard served in 2019 as acting branch chief of the EPA’s risk assessment branch evaluating paraquat. Before joining the EPA in 2009, Rickard worked for CropLife America, the powerful Washington-based lobbying organization that represents the pesticide industry.

The EPA did not comment.

“One of the most significant threats to human health [EPA] comes from the wide open door between regulators and industry,” said Nathan Donley, director of environmental health sciences at the Center for Biological Diversity. The nonprofit group is among several organizations challenging the EPA’s paraquat assessment in federal court.

“Croplife’s sole purpose is to get the pesticide industry to do whatever it wants,” Donley said. “Someone in this world should not be making decisions that have such a huge impact on public health.”

Rickard now works as a senior scientific evaluator at Health Canada and did not respond to a request for comment.

California ban requested

In response to the legal challenge to its assessment of paraquat, the EPA said in late September that it would reconsider “aspects” of its decision to keep paraquat on the market and issue an addendum to its assessment within a month. year.

Meanwhile, as they continue to push the EPA to ban paraquat, some groups worried about the chemical are also trying to convince California to stop its use. As a major agricultural state, a ban in California would force the state to take similar action in other states, say those calling for a ban.

The Center for Biological Diversity said it will formally ask the state to reevaluate and ban paraquat before the next annual reapproval of all pesticide ingredients in 2023.

Donley said decades of internal Syngenta corporate documents recently revealed in the Guardian and New Lede support the need to stop weedkiller use.

“We think there is a strong enough case to re-examine paraquat due to Parkinson’s disease,” Donley said. “You have to consider all the evidence, and when you do, it paints a pretty clear picture.”

This story is co-published with the New Lede, an environmental working group journalism project. Carey Gillam is editor of The New Lede.

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