A broad new scientific analysis of the carcinogenic potential of glyphosate herbicides, the world's most widely used weedkiller, has shown that people with high levels of exposure to the popular pesticides have a 41% increased risk of developing a so-called cancer -Hodgkin lymphoma.
The evidence "supports a compelling link" between exposure to glyphosate-based herbicides and increased risk of non-Hodgkin's lymphoma (NHL), the authors concluded, although the specific numerical risk assessments should be interpreted with caution.
The findings of five US scientists contradict US Environmental Protection Agency (EPA) safety reviews of weed killers, and regulators in several countries are considering limiting the use of glyphosate-based products in agriculture.
Monsanto and its German owner, Bayer AG, face more than 9,000 lawsuits in the US brought by NHL sufferers blaming Monsanto's glyphosate-based herbicides for their illnesses. The first plaintiff, who was brought to trial, unanimously won a jury verdict against Monsanto in August, a ruling that appeals to the company. The next hearing, involving a separate claimant, is due to begin on 25 February and several more trials are planned for this year and for 2020.
Monsanto claims that there are no legitimate scientific studies demonstrating a clear link between glyphosate and NHL or any type of cancer. Company officials say the EPO's finding that glyphosate "probably will not cause cancer" is supported by hundreds of studies that find no such link.
The company claims that scientists at the International Agency for Research on Cancer (IARC), which classified glyphosate as a probable human carcinogen in 2015, have engaged in inappropriate behavior and failed to adequately acknowledge several important studies.
However, the new analysis may potentially complicate Monsanto's defense against the best-selling herbicide. Three of the authors of the study were appointed by the EPO as board members for a Scientific Advisory Board on Glyphosate 2016. The new paper was published by Mutation Research / Reviews in Mutation Research, whose editor-in-chief is EPA researcher David DeMarini.
The authors of the study say their meta-analysis is different from previous reviews. "This paper is a more convincing case than previous meta-analyzes that there are signs of increased NHL risk due to glyphosate exposure," said co-author Lianne Sheppard, a professor in the Department of Environmental and Health Sciences at the University of Washington. "From a health point of view, there are some real concerns."
Sheppard was one of the EPA's scientific advisers on glyphosate and was among a group of counselors who told the EPA that they had not followed the proper scientific protocols and had determined that glyphosate was unlikely to cause cancer. "It was wrong," Sheppard said about the EPA rating of glyphosate. "It was pretty obvious they were not following their own rules. Is there evidence that it is carcinogenic? The answer is yes. "
An EPA spokesman said, "We're reviewing the study." Bayer, who bought Monsanto in the summer of 2018, did not respond to a request for comment on the study.
A Bayer opinion on glyphosate cites the EPA assessment and states that glyphosate herbicides have been "extensively tested" and have proven to be a "safe and efficient weed control tool".
The authors of the study indicated that their new meta-analysis has evaluated all published human studies, including a 2018 updated, government-funded study known as the Agricultural Health Study (AHS). Monsanto has cited the updated AHS study as proof that there is no link between glyphosate and NHL. In conducting the new meta-analysis, researchers said they focused on the highest exposed group in each study, as these individuals would most likely be at increased risk if glyphosate herbicides cause NHL.
If you only consider persons who have a high pesticide load in the real world, it is less likely that interfering factors can influence the results, the authors said. In essence, if there is no real correlation between the chemical and cancer, even highly exposed individuals should not develop significant cancer.
In addition to human studies, researchers also investigated other types of glyphosate studies, including many animal studies.
"All meta-analyzes so far, including our own, consistently report the same result: GBH exposures are associated with an increased NHL risk," the researchers concluded.
David Savitz, a professor of epidemiology at Brown University's School of Public Health, said the work was "well done," but "fundamentally new information" was missing.
"I would suggest that the concern and the need for a rating remain, but the question is not finally settled," Savitz said.
Carey Gillam is a journalist, author, and researcher in the public interest for US Right to Know, a nonprofit food industry research group