A common herbicide ingredient replacing glyphosate in the United States has been found to cause multiple types of organ damage and kill gut bacteria, according to new research. Despite its documented toxicity, the Environmental Protection Agency has resisted banning the chemical, even as other countries take action to protect public health.
Diquat, a bipyridyl herbicide, is widely used for its high efficacy in weed control. “Diquat is a widely used bipyridyl herbicide that is extensively applied in agricultural production and water management due to its high efficacy in weed control. However, its environmental persistence and the toxic effects it induces have raised widespread concern,” the authors of the analysis wrote.
Primarily sprayed in orchards and vineyards, diquat use has increased as reliance on controversial substances like glyphosate and paraquat has decreased. “From a human health perspective, this stuff is quite a bit nastier than glyphosate so we’re seeing a regrettable substitution, and the ineffective regulatory structure is allowing it,” said Nathan Donley, science director with the Center For Biological Diversity.
The new scientific review found that diquat kills gut bacteria and harms multiple organs. “Studies show that Diquat primarily enters the body through the digestive tract, leading to poisoning,” the authors wrote.
A Friends of the Earth analysis of EPA data in October found diquat to have roughly 200 times the toxicity of glyphosate in terms of chronic exposure. The chemical is believed to be a carcinogenic neurotoxin with a potential link to Parkinson’s disease.
The core mechanism of diquat’s toxicity involves reactive oxygen species (ROS)-induced oxidative stress, according to the authors. “The core mechanism of its toxicity involves reactive oxygen species (ROS)-induced oxidative stress, which not only directly damages the intestinal barrier function but also exacerbates inflammation and systemic toxicity by disrupting the balance of the gut microbiota and the normal production of metabolic products,” the study stated.
The weakening of the gut lining allows pathogens and toxins to enter the bloodstream, triggering intestinal and bodily inflammation. The damage interferes with nutrient absorption and energy metabolism.
Beyond gut damage, diquat harms other organs. It “causes irreversible structural and functional damage to the kidneys” by destroying kidney cell membranes and interfering with cell signaling. Effects on the liver are similar, as diquat causes production of proteins that inflame the organ. In the lungs, the chemical triggers inflammation that damages tissue and may contribute to multiple organ dysfunction syndrome.
Due to these risks, diquat has been banned in the European Union, China, the United Kingdom, and many other countries. However, the EPA is not currently conducting a review of diquat. Donley said that’s partially because diquat is “overshadowed” by ingredients like paraquat, glyphosate, and chlorpyrifos, which are the focus of legal and regulatory battles despite being banned elsewhere.
“Other countries have banned diquat, but in the US we’re still fighting the fights that Europe won 20 years ago,” Donley said. “It hasn’t gotten to the radar of most groups and that really says a lot about the sad and sorry state of pesticides in the US.”
Bayer, which makes Roundup, has faced nearly 175,000 lawsuits alleging harm from glyphosate-based products. The company reformulated Roundup after the International Agency for Research on Cancer classified glyphosate as a possible carcinogen. New Roundup formulas containing diquat have since entered the US market.
The authors of the analysis noted that many existing studies on diquat’s toxicity have been conducted on rodents and called for more research on the effects of low-dose, long-term exposure in humans.
Donley said the EPA’s pesticides office views toxic pesticides as a “necessary evil” and that the agency’s philosophy limits its willingness to act. “When you approach an issue from that lens there’s only so much you will do,” he said.
As the US continues to allow use of chemicals banned elsewhere, advocates warn that weak regulations and “regrettable substitutions” will continue to put public health at risk.
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