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The Link Between Parkinson’s Disease and the Pesticide Paraquat

Once again, a pesticide banned in many other countries due to its harmful effects on humans and the environment, is allowed to be used in the US. The incredibly dangerous pesticide paraquat is banned in more than 70 countries, including China (where it is made), but not the US. Paraquat (paraquat dichloride) is a highly toxic weed killer used by farmers.

Many studies and farmers themselves report that paraquat causes Parkinson's disease. Currently there are thousands of lawsuits against Syngenta, the manufacturer, and Chevron USA (the seller). [NOTE: Of course Syngenta denies any link between paraquat exposure and Parkinson's disease.] The US Geological Survey reports that between 11 million and 17 million pounds of paraquat are sprayed annually on American farms. But here's the crazy part: use of the pesticide in the US is increasing annually. WTH?

By the way, Parkinson’s disease is the fastest growing neurological disorder in the world, with about 90,000 new cases diagnosed each year in the US. A number of pesticides are linked with the increase, with the link between paraquat and Parkinson's disease known since the 1980s (by research done by independent researchers). Evidence is growing that it's not just direct exposure (contact with it), but also chronic low level exposure that is linked to Parkinson's disease (e.g., living near a farm - thus inhalation of low levels in the air).

What will it take to ban the use of paraquat in the US? (Yes, there are alternatives to paraquat.) Doesn't look likely in the near future. In fact, the chemical/pesticide industry is trying to pass state and federal laws that would protect pesticide manufacturers from liability.

Excerpts from an investigative piece. From nj.com news: Thousands of U.S. farmers have Parkinson’s. They blame a deadly pesticide.

Paul Friday remembers when his hand started flopping in the cold weather – the first sign nerve cells in his brain were dying.

He was eventually diagnosed with Parkinson’s, a brain disease that gets worse over time. His limbs got stiffer. He struggled to walk. He couldn’t keep living on his family farm. Shortly afterward, Friday came to believe that decades of spraying a pesticide called paraquat at his peach orchard in southwestern Michigan may be the culprit.

The pesticide, a weed killer, is extremely toxic.

With evidence of its harms stacking up, it’s already been banned in dozens of countries all over the world, including the United Kingdom and China, where it’s made. Yet last year, its manufacturer Syngenta, a subsidiary of a company owned by the Chinese government, continued selling paraquat in the United States and other nations that haven’t banned it.

Health statistics are limited. Critics point to research linking paraquat exposure to Parkinson’s, while the manufacturer pushes back, saying none of it is peer-reviewed. But the lawsuits are mounting across the United States, as farmers confront Parkinson’s after a lifetime of use, and much of the globe is turning away from paraquat.

It has many critics wrestling with the question: What will it take to ban paraquat in the United States?

“What we’ve seen over the course of decades is a systemic failure to protect farmworkers and the agricultural community from pesticides,” said Jonathan Kalmuss-Katz, a senior attorney at Earthjustice, an environmental law organization that advocates against paraquat.

Krause is one of thousands of people who have sued Syngenta, a manufacturer, and Chevron USA, a seller, over paraquat exposure. They’re alleging the chemical companies failed to warn of the dangers of paraquat despite knowing it could damage human nerve cells and studies showing it’s linked to Parkinson’s disease.

In Ohio, there’s Dave Jilbert a winemaker who sprayed the pesticide on his vineyard south of Cleveland. He was diagnosed with Parkinson’s in 2020 and now he is suing and working to get paraquat banned. Terri McGrath believes years of exposure to paraquat at her family farm in rural Southwest Michigan likely contributed to her Parkinson’s. Six other family members also have the disease. And in south Alabama, Mac Barlow is suing after receiving a similar diagnosis following years of relying on paraquat.

Since hitting the market in the 1960s, paraquat has been used in farming to quickly “burn” weeds before planting crops. The pesticide, originally developed by Syngenta and sold by Chevron, rips tissue apart, destroying plants on a molecular level within hours.

“It’s used because it’s effective at what it does. It’s highly toxic. It’s very good at killing things,” said Geoff Horsfield, policy director at the Environmental Working Group. “And unfortunately, when a pesticide like this is so effective that also means there’s usually human health impacts as well.”

Because paraquat kills any growth it touches, it’s typically used to clear a field before any crops are planted. Low levels of paraquat residue can linger on food crops, but the foremost threat is direct exposure.

The U.S. Environmental Protection Agency already restricts paraquat, labeling it as “registered use,” with a skull and crossbones, meaning it can only be used by people who have a license. Because of its toxicity, the federal government requires it to have blue dye, a sharp smell and a vomiting agent, according to the U.S. Centers for Disease Control, CDC. Sprayers are also told to wear protective gear.

Swallowing is the most likely way to be poisoned by paraquat, according to the CDC, but skin exposure can also be deadly. In fact, if it spills on someone, health officials say they should wash it off immediately and quickly cut off their clothes. That way they don’t risk spreading more deadly pesticide on their body as they pull their shirt over their head.

Even secondary exposure can be dangerous. One case published in the Rhode Island Medical Journal described an instance where a 50-year-old man accidentally ingested paraquat, and the nurse treating him was burned by his urine that splashed onto her forearms. Within a day, her skin blistered and sloughed off.

Meanwhile, a much more widespread threat looms large in the background: long-term, low-level exposure.

Parkinson’s disease is the fastest growing neurological disorder in the world, with cases projected to double by 2050, partly due to an aging population, according to a study published in The BMJ, a peer-reviewed medical journal. It occurs when the brain cells that make dopamine, a chemical that controls movement, stop working or die.

A Parkinson’s Foundation study found that 87% of those with the disease do not have any genetic risk factors. That means, “for the vast majority of Americans, the cause of Parkinson’s disease lies not within us, but outside of us, in our environment,” said neurologist and researcher Ray Dorsey.

That’s why Dorsey, who literally wrote the book on Parkinson’s, calls the disease “largely preventable.” There’s a long list of environmental factors linked to Parkinson’s, but pesticides are one of the biggest threats, according to Dorsey. “If we clean up our environment, we get rid of Parkinson’s disease,” he said.

An early 1987 case report published in Neurology discusses the case of a 32-year-old citrus farmer who started experiencing tremors, stiffness and clumsiness after 15 years of spraying paraquat. But “a cause-and-effect relationship is difficult to establish,” a doctor wrote at the time.

A decade later, an animal study from Parkinson’s researcher Deborah Cory-Slechta found that paraquat absorbed by mice destroys the specific type of dopamine neuron that dies in Parkinson’s disease. More recently, her research has found paraquat that’s inhaled can also bypass the blood-brain barrier, threatening neurons. “It’s quite clear that it gets into the brain from inhalation models,” Cory-Slechta said.

Critics point to other epidemiological studies being more definitive. In 2011, researchers studied farmworkers exposed to two pesticides, rotenone and paraquat, and determined those exposures increased the risk of developing Parkinson’s by 150%. Another study, published last year, looked at 829 Parkinson’s patients in central California. It found people who live or work near farmland where paraquat is used have a higher risk of developing the disease.

“It’s kind of like secondhand smoke,” Dorsey said. “You can just live or work near where it’s sprayed and be at risk.”

This is a growing concern in American suburbs where new houses press up against well-maintained golf courses. A study published in JAMA this year found that living within a mile of a golf course increased the risk of Parkinson’s disease by 126%. It didn’t name specific chemicals but did point to pesticides.

What company files show

A trove of internal documents released during litigation, as reported by The Guardian and the New Lede, appeared to show that the manufacturers were aware of evidence that paraquat could collect in the brain.

The trail of bread crumbs started as early as 1958 when a company scientist wrote about a study of 2.2 dipyridyl, a chemical in paraquat, saying it appears to have moderate toxicity “mainly by affecting the central nervous system, and it can be absorbed through the skin,” the internal documents said.

The internal documents show by 1974, the company updated safety precautions, recommending that anyone spraying the pesticide wear a mask, as there were the first reports of human poisoning and concerns about the effects of paraquat started to grow.

By the 1980s, outside research started to pick at the question of paraquat and Parkinson’s. “As more researchers dug into it, it’s only been more firmly established,” said Horsfield with the Environmental Working Group.

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