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New analysis raises questions about EPA’s classification on glyphosate weed killer

Researcher says the EPA has disregarded substantial evidence that the popular herbicide is linked to cancer

A little more than a month ahead of a first-ever federal trial over the issue of whether or not Monsanto's popular weed killers can cause cancer, a new analysis raises troubling questions about the U.S. Environmental Protection Agency's (EPA) handling of pertinent science on glyphosate safety.


According to the report, which examines the opposing positions taken by the EPA and an international cancer research agency on glyphosate-based herbicides, the EPA has disregarded substantial scientific evidence of genotoxicity associated with weed killing products such as Roundup and other Monsanto brands. Genotoxicity refers to a substance's destructive effect on a cell's genetic material. Genotoxins can cause mutations in cells that can lead to cancer.

The EPA classifies glyphosate as not likely to be carcinogenic while the International Agency for Research on Cancer (IARC), which is part of the World Health Organization, classifies it as "probably carcinogenic."

The paper was authored by Charles Benbrook, a former research professor who served at one time as executive director of the National Academy of Sciences board on agriculture, and was published in the journal Environmental Sciences Europe on Monday. It is based on Benbrook's review of EPA and IARC records regarding the types and numbers of glyphosate studies each organization evaluated.

"Clearly, compared to EPA's genotoxicity review, the IARC review is grounded on more recent, more sensitive, and more sophisticated genotoxic studies, and more accurately reflects real-world exposures," Benbrook told EHN.

Benbrook testified as an expert witness in the first lawsuit to go to trial against Monsanto over claims its glyphosate herbicides cause cancer. The plaintiff in that case, Dewayne "Lee" Johnson, won a unanimous jury award of $289 million last year that the judge in the case cut to $78 million. Thousands of additional cancer victims have sued Monsanto and the second trial begins Feb. 25 in federal court in San Francisco. Benbrook is also expected to testify for the plaintiff in that case.

Monsanto is seeking to exclude Benbrook's testimony at trial, saying he has no expertise in any physical science or field of medicine and no training or degree in toxicology and has never worked at the EPA or other regulatory body.

The EPA did not respond to a request for comment. The agency has maintained, however, that its review of glyphosate has been robust and thorough. Glyphosate has low toxicity for humans and glyphosate products can be safely used by following directions on labeled products, according to the EPA.

In the new analysis, Benbrook is critical of the EPA's scrutiny of glyphosate herbicides, noting that little weight was given to research regarding the actual formulations sold into the marketplace and used by millions of people around the world. Instead, the EPA and other regulators have mostly pointed to dozens of studies paid for by Monsanto and other companies selling glyphosate herbicides that found no cancer concerns. The EPA has given little attention to several independent research projects that have indicated the formulations can be more toxic than glyphosate alone, according to Benbrook.

Indeed, the EPA only started working in 2016—some 42 years after the first glyphosate herbicides came to market – with the U.S. National Toxicology Program to evaluate the comparative toxicity of the formulations. Early results disclosed in 2018 supported concerns about enhanced toxicity in formulations.

Several scientists, including from within the EPA's Office of Research and Development (ORD), and from a panel of scientific experts convened by the EPA, have cited deficiencies and problems with the EPA's decision to classify glyphosate as not likely to be carcinogenic to humans. But Benbrook's analysis is the first to look deeply at how and why the EPA and IARC drew such divergent conclusions.

Benbrook looked at the citations for genotoxicity tests discussed in the EPA and IARC reports, both those that were published in peer-reviewed journals and the unpublished ones that were presented to the EPA by Monsanto and other companies.

Some studies looked at glyphosate alone, and/or glyphosate-based herbicide formulations and some included findings about a substance called aminomethylphosphonic acid (AMPA), which is glyphosate's primary metabolite.

Benbrook's analysis found that within the body of available evidence, the EPA relied on 151 studies, 115 of which showed negative results, meaning no evidence of genotoxicity, and only 36 that had positive results. IARC cited 191 studies, only 45 of which showed negative results and 146 of which showed evidence of genotoxicity.

IARC said within these studies it found "strong evidence that exposure to glyphosate or glyphosate-based formulations is genotoxic…"

Benbrook's analysis reports that over the last three years at least 27 additional studies have been published addressing possible mechanisms of genotoxic action for glyphosate and/or formulated glyphosate-based herbicides and all but one of the 27 studies reported one or more positive result. There were 18 positives arising from DNA damage, six associated with oxidative stress, and two with other genotoxicity mechanisms, his paper states.

According to Benbrook, the EPA's failure to focus on formulated glyphosate-based herbicides is dangerous because these formulations "account for all commercial uses and human exposures (no herbicide products contain just glyphosate)."

More research is needed on real-world exposures, Benbrook concludes.

Carey Gillam is a journalist and author, and a public interest researcher for US Right to Know, a not-for-profit food industry research group. Follow her on Twitter at @careygillam.

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