A team of 17 cancer experts assembled by the World Health Organization has ruled the most commonly used herbicide a “probable carcinogen.”
Glyphosate—the active ingredient in Roundup weedkiller—was developed by Monsanto in the 1970s. It is now the most commonly produced herbicide in the world; used in home gardens, public parks and on the vast majority of acres planted with corn or soybeans in the U.S.
That means the pool of people who are potentially exposed to glyphosate is huge.
Dr. Aaron Blair, a cancer epidemiologist from the National Institutes of Health, chaired the team of scientists who issued the ruling after reviewing all available medical literature. He says animal studies linked glyphosate to some cancers, but human studies (including ones he contributed to) showed a limited correlation.
“There were enough studies to suggest something was going on, but not enough to be sure that was absolutely happening,” Blair said. “When [the evidence] is limited in humans and sufficient in animals, it’s the classification that it’s ‘probably carcinogenic’ in humans.”
The decision, published March 20 in Lancet Oncology, cites research from the U.S., Canada and Sweden that found links between non-Hodgkin’s lymphoma and exposure to glyphosate among farmworkers.
In a press release, Monsanto called the report “junk science.”
Monsanto’s vice president of global regulatory affairs, Phil Miller, said he was “disappointed and outraged” by the committee’s conclusion.
“I’ve looked at this information, I have a responsibility to view it every day, as well as the regulatory agencies. Time and time again they have come to the conclusion that this product is safe for human health and the environment,” Miller said.
The U.S. Environmental Protection Agency assessed human health risks associated with glyphosate in 2012, and found it met statutory safety standards. The compound is currently being reassessed as part of a 15-year, scheduled re-evaluation that will include both human and ecological safety risks.
“We will give full consideration to the IARC study and all the other information we have before we reach a final decision,” the EPA said in a statement. "If at any time EPA discovers that the use of a registered pesticide may result in unreasonable adverse effects on people or the environment, we will take action to remove it from the marketplace or limit its use."