Florida study suggests weed killer Roundup could contribute to Parkinson's Disease

The tiny worms quiver into seizures when Akshay Naraine introduces even trace amounts of Roundup to fray their nematode nerves.

His new research shows the popular herbicide triggers "seizure-like" effects on the nervous system of roundworms — a good proxy for how human nerve cells work — even at 300 times less than the lowest levels recommended for consumer use.

In the roundworms, Roundup targets the same neurotransmitter receptors in humans that regulate sleep and mood. So when their function gets derailed by the weed killer and its key ingredient, glyphosate, it can contribute to depression and anxiety, or chronic neurodegenerative diseases such as Parkinson's, studies show.

"It's like a train track," Naraine, the latest study's project lead and Ph.D. student at Florida Atlantic University, said of the nerve pathway Roundup and glyphosate disrupt. The key question, he said: "Is it diverting the train or destroying the train track?"

Naraine's study, along with colleagues at Nova Southeastern University, concluded the former: Roundup and glyphosate divert "the train" but don't destroy the "tracks" of the nerve infrastructure. But it still can cause neurological train wrecks that have implications for Parkinson's Disease, anxiety, depression and other nervous system disorders, maybe even for threatened Florida manatees and other wildlife.

The U.S. Environmental Protection Agency for decades has denied evidence that glyphosate causes cancer in humans. But scientific evidence keeps mounting of the herbicide's carcinogenic and other health risks to humans and wildlife.

Naraine's study comes in the wake of a U.S. Centers for Disease Control and Prevention research released last month that found eight in 10 Americans have glyphosate in their urine.

Naraine's study, published in Scientific Reports, showed glyphosate and Roundup increased seizure-like behavior in soil-dwelling roundworms. The research provides significant evidence that glyphosate targets neurotransmitter receptors — communication points in nerve cells — essential for motion in worms and "heavily involved in regulating sleep and mood in humans."

Glyphosate long had been considered one of the safest herbicides because it inhibits synthesis of certain amino acids in plants along a metabolic pathway that doesn't occur in vertebrates. But studies in recent years show animals chronically exposed to the herbicide develop liver and kidney disease.

The FAU and Nova Southeastern study adds to the mounting evidence that the popular weed killer, vital for food supplies, pose unacceptable health risks.

A broad-scoping study in 2019 found high exposures to the herbicide poses a 41% increased risk of developing non-Hodgkin lymphoma.

Under thousands of lawsuits from lawn and garden uses for exposure to the herbicide, agrochemical giant Bayer announced last year it would replace Roundup that contains glyphosate with products that do not and remove versions that do from shelves by next year.

The company issued a statement Thursday in response to FAU's study: "It is important to note that this research was conducted with worms," the statement said. "Research with worms does not meet the scientific standards necessary to predict effects on humans or other mammals for the purposes of a pesticide safety assessment."

Scientists at regulatory agencies have reviewed glyphosate worldwide and the other ingredients in glyphosate-based herbicides and specifically considered whether they can harm the nervous system based on data from high dose studies in mammals, not worms, the company added. "Scientists that have reviewed all of the available data have concluded that neither glyphosate nor the other ingredients in glyphosate-based herbicides will harm the nervous system at doses much greater than what any human would be exposed to."

Nonetheless, three years ago, Martin County banned contractors and county employees from using glyphosate.

“It is concerning how little we understand the impact of glyphosate on the nervous system,” said Naraine, the project lead and a Ph.D. student at FAU and the International Max Planck Research School for Synapses and Circuits, said in a release. “More evidence is mounting for how prevalent exposure to glyphosate is, so this work hopefully pushes other researchers to expand on these findings and solidify where our concerns should be.”

Naraine found the weed killer disrupted nerve cell transmission in roundworms in ways analogous to humans and animals. What sets the research apart, he says, is that it showed harmful effects of herbicides at significantly lower concentrations than what EPA recommends as safe and those used in past studies.

The level listed for best results on the Roundup Super Concentrate label is 0.98% glyphosate, about 5 tablespoons of Roundup in one gallon of water, Naraine notes.

"A significant finding from our study reveals that just 0.002% glyphosate, a difference of about 300 times less herbicide than the lowest concentration recommended for consumer use, had concerning effects on the nervous system,” Naraine said.

Antiepileptic drugs to the rescue

More than one in three worms in the study failed to rebound from their convulsions, after Naraine exposed them to Roundup. But those given an anti-epilepsy treatment fully bounced back to their previous wormy ways, indicating the nerve cells can recover normal function, if spared exposure to Roundup and glyphosate, Naraine said.

"Key to our initial hypothesis, we found that treatment with an antiepileptic drug rescued the prolonged convulsions," the study authors wrote.

What about manatees?

Biologists hope better understanding of how herbicides block neurotransmission might provide clues into how herbicides might contribute to manatee health problems, as well as other marine mammals.

A paper released in March 2021 by University of Florida found an increasing body burden of glyphosate in manatees’ blood plasma, with higher levels before and during sugar cane harvest. The UF researchers found more than half of Florida's manatees have glyphosate in their bodies.

Starving manatees in Florida overwhelming rescuers

For years, in absence of seagrass in the Indian River Lagoon, manatees have been eating more of the thick seaweed-like drift macroalgae, because microalgae blooms have choked out their usual seagrass diet. Some research shows glyphosate also can worsen algae blooms, because as it breaks down it releases phosphorus that fuels algae growth.

Scientists had suspected manatees were succumbing to a toxin that affects their nervous system, hampering the marine mammal's ability to surface, causing it to drown. But several typical algae toxins have not shown up in testing.

So marine biologists have yet to unravel what the glyphosate's presence means for the health of sea cows, not to mention humans.

"It's so important to our food supply and how we get our food," Naraine said of the herbicide, "so it is pertinent to understand if there is any cause for concern."

Jim Waymer is an environment reporter at FLORIDA TODAY. Contact Waymer at 321-242-3663 or jwaymer@floridatoday.com. Or find him on Twitter: @JWayEnviro or on Facebook: www.facebook.com/jim.waymer

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This article originally appeared on Florida Today: Florida study finds low levels of weed killer Roundup can be harmful