“It sucks,” said Mund, 69. He speaks tersely, because every word is a hard-won battle. “I was told the herbicide wouldn’t hurt you.”
The herbicide is paraquat, an extremely powerful weed killer that Mund sprayed on vegetation as part of his job from about 1980 to 1985. Mund contends the product is responsible for his disease, but the manufacturer denies there is a causal link between the chemical and Parkinson’s. Weed Killer For Ivy
But research suggests the chemical may cross the blood-brain barrier in a manner that triggers Parkinson’s disease, a progressive neurodegenerative disorder that affects movement. Now, Mund is among thousands of workers suing Syngenta seeking damages and hoping to see the chemical banned.
Since 2017, more than 3,600 lawsuits have been filed in state and federal courts seeking damages from exposure to paraquat products, according to Syngenta’s 2022 financial report.
“Despite decades of investigation and myriad epidemiological and laboratory studies, no scientist or doctor — whether or not affiliated with Syngenta — has ever concluded in a peer-reviewed scientific analysis that paraquat causes Parkinson’s,” the company’s chief communications officer, Saswato Das, wrote in an email.
Some scientists contend they commonly use paraquat to induce Parkinson’s disease in mice as part of research studies, said Ray Dorsey, a professor of neurology at the University of Rochester in New York and the author of “Ending Parkinson’s Disease.”
“There have been numerous academic researchers over the last 20-plus years — and multiple different investigators in multiple different locations — that have found that paraquat, when fed to laboratory animals, reproduces the features of Parkinson’s disease,” Dorsey said.
He referenced an oft-cited 2011 study funded by the National Institutes of Health that found a strong association between Parkinson’s and paraquat. It found that workers exposed to paraquat had a 250% greater risk of getting Parkinson’s disease than people not exposed to the chemical. “Because paraquat remains one of the most widely used herbicides worldwide, this finding potentially has great public health significance,” the study concluded.
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Groups such as Earthjustice and the Michael J. Fox Foundation have been pushing for years to ban paraquat, with the latter noting on its website that the herbicide is “thought to increase Parkinson’s risk by 100 to 500% , depending on overall exposure.”
Paraquat is 28 times more toxic than another controversial herbicide, Roundup, according to a report from the Pesticide Action Network. (Roundup has been banned in several parts of California, including a 2019 moratorium by the Los Angeles County Board of Supervisors forbidding its use by county departments.)
Paraquat also has other known health effects. It is listed as “highly toxic” on the U.S. Environmental Protection Agency’s website, which says that “one small sip can be fatal and there is no antidote.” The EPA is currently reviewing paraquat’s approval status.
However, paraquat was significantly associated with the disease among those who reported a history of head injuries, with a more than threefold increase in risk based on a small number of cases with both exposures, said Sandler, who is also head of the epidemiology branch at the National Institute of Environmental Health Sciences.
Multiple sources said the dizzying array of competing research is a reflection of industry pushback, political lobbying and deep-pocketed agribusiness. Syngenta reported a record $33 billion in sales in 2022. One leading researcher on the matter said she has been retained as a witness in pending lawsuits and so was not comfortable commenting publicly for this report.
12:46 p.m. Dec. 20, 2023 An earlier version of this article said documents were unveiled as part of ongoing court proceedings in Illinois. The proceedings are in California.
In a 2022 deposition, Syngenta’s principal science advisor, Philip Botham, acknowledged that the company made a considerable effort to obtain the data used in that study and conducted its own analysis, which reached the same conclusion about the incidence of the disease, according to a transcript of his testimony. However, the finding was not publicized and Botham did not divulge it in a subsequent interview with the New York Times.
Another transcript indicates that Syngenta attempted to downplay studies showing that paraquat administered to mice caused a reduction in the number of dopamine cells in the substantia nigra, the part of the brain that produces dopamine, which is another hallmark of Parkinson’s disease.
Das, of Syngenta, dismissed the 2011 study as an “interim study that looked at only part of the data,” adding that the findings were later expanded upon and improved in the 2020 study that found no clear link.
Regarding dopamine loss in mice, he said the animals in those studies were given doses “as much as 22,000 times higher than the highest amount of exposure found in U.S. farmers” and that animal studies cannot be used to prove causation. He said the majority of Marks’ findings were not reported to the EPA because they were materially similar to what was already in the public literature.
“In short, the hypothesis that paraquat causes Parkinson’s is not accepted in the medical community or peer-reviewed science, nor has it been accepted at any time in the past,” he said.
DDT was banned 50 years ago, but its toxic legacy continues to affect the California marine ecosystem and threaten various animal species.
Still, Syngenta has paid at least $187.5 million into its settlement fund as of 2021, according to its financial report. One attorney involved in California litigation estimated that there are at least 300 active plaintiffs in the state and at least 4,500 in the country.
In Mund’s legal complaint, attorneys ague that the companies “failed to warn that paraquat was likely to cause neurological damage that was both permanent and cumulative, and repeated exposures were likely to cause clinically significant neurodegenerative disease, including Parkinson’s disease.”
In California, at least, the debate rages on.
Last year, half a dozen researchers, including Okun and Dorsey, signed a letter to the California Department of Pesticide Registration urging it to reconsider use of the chemical. The letter warned that “paraquat presents a public health hazard to residents and workers in the state of California.”
“It’s been a long-term process,” Tammie said as she pointed to a fresh scab on her husband’s scalp from a recent fall.
Mund said he has no relatives with Parkinson’s and that a medical test confirmed his case was not genetic. But he did have a co-worker who was also diagnosed with Parkinson’s and later died, he said.
“They banned DDT back in the ’60s,” Mund said, asking why the same hasn’t happened for paraquat.
“We’d like to see it banned,” she said.
Hayley Smith is an environment reporter for the Los Angeles Times, where she covers the many ways climate change is reshaping life in California, including drought, floods, wildfires and deadly heat.
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