The herbicide ingredient used to replace glyphosate in Roundup and other weedkiller products can kill gut bacteria and damage organs in multiple ways, new research shows.
The ingredient, diquat, is widely employed in the US as a weedkiller in vineyards and orchards, and is increasingly sprayed elsewhere as the use of controversial herbicide substances such as glyphosate and paraquat drops in the US.
But the new piece of data suggests diquat is more toxic than glyphosate, and the substance is banned over its risks in the UK, EU, China and many other countries. Still, the EPA has resisted calls for a ban, and Roundup formulas with the ingredient hit the shelves last year.
“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, which advocates for stricter pesticide regulations but was not involved in the new research. “Regrettable substitution” is a scientific term used to describe the replacement of a toxic substance in a consumer product with an ingredient that is also toxic.
Diquat is also thought to be a neurotoxin, carcinogen and linked to Parkinson’s disease. An October analysis of EPA data by the Friends of the Earth non-profit found it is about 200 times more toxic than glyphosate in terms of chronic exposure.
Bayer, which makes Roundup, faced nearly 175,000 lawsuits alleging that the product’s users were harmed by the product. Bayer, which bought Monsanto in 2018, reformulated Roundup after the International Agency for Research on Cancer classified glyphosate as a possible carcinogen.
The new review of scientific literature in part focuses on the multiple ways in which diquat damages organs and gut bacteria, including by reducing the level of proteins that are key pieces of the gut lining. The weakening can allow toxins and pathogens to move from the stomach into the bloodstream, and trigger inflammation in the intestines and throughout the body. Meanwhile, diquat can inhibit the production of beneficial bacteria that maintain the gut lining.
Damage to the lining also inhibits the absorption of nutrients and energy metabolism, the authors said.
The research further scrutinizes how the substance harms the kidneys, lungs and liver. Diquat “causes irreversible structural and functional damage to the kidneys” because it can destroy kidney cells’ membranes and interfere with cell signals. The effects on the liver are similar, and the ingredient causes the production of proteins that inflame the organ.
Meanwhile, it seems to attack the lungs by triggering inflammation that damages the organ’s tissue. More broadly, the inflammation caused by diquat may cause multiple organ dysfunction syndrome, a scenario in which organ systems begin to fail.
The authors note that many of the studies are on rodents and more research on low, long-term exposure is needed. Bayer did not immediately respond to a request for comment.
Despite the risks amid a rise in diquat’s use, the EPA is not reviewing the chemical, and even non-profits that push for tighter pesticide regulations have largely focused their attention elsewhere.
Donley said that was in part because US pesticide regulations are so weak that advocates are tied up with battles over ingredients like glyphosate, paraquat and chlorpyrifos – substances that are banned elsewhere but still widely used here. Diquat is “overshadowed” by those ingredients.
“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.”
Some advocates have accused the EPA of being captured by industry, and Donley said US pesticide laws were so weak that it was difficult for the agency to ban ingredients, even if the will exists. For example, the agency banned chlorpyrifos in 2022, but a court overturned the decision after industry sued.
Moreover, the EPA’s pesticides office seems to have a philosophy that states that toxic pesticides are a “necessary evil”, Donley said.
“When you approach an issue from that lens there’s only so much you will do,” he said.