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New Study Provides Further Evidence of Cancer-Causing Potential of World's Leading Herbicide

February 14, 2019
Center for Food Safety

New Study Provides Further Evidence of Cancer-Causing Potential of World's Leading Herbicide

Roundup and Other Glyphosate Formulations Shown to Damage DNA

A new study, published January 14th in Environmental Sciences Europe, provides powerful new evidence in support of the classification of glyphosateâ??the world's most widely used herbicideâ??as "probably carcinogenic to humans." Glyphosate is the active ingredient in Monsanto's Roundup and related products.

The study reviews the findings of over 200 genotoxicity assays conducted to determine if glyphosate-based herbicides (GBHs) can damage DNA, one pathway to cancer, or trigger other cancer-causing changes in cells. The assays involved tests in which bacteria, mammalian cell cultures, or live animals were exposed to pure glyphosate or formulated GBHs (the products that people spray and are exposed to). A few studies involved people unintentionally exposed to the herbicide.

Nearly all of the tests commissioned by pesticide companies like Monsanto reported negative results, while the majority of peer-reviewed studies by independent scientists showed that glyphosate herbicides are genotoxic.

The study compares how the World Health Organization's International Agency for Research on Cancer (IARC) and the U.S. Environmental Protection Agency (EPA) assessed the genotoxicity results. IARC officially classified glyphosate as "probably carcinogenic" in 2015, as has the State of California, while EPA has found it not likely to cause cancer.

"The study reveals three stark differences in how IARC and EPA evaluated the genotoxicity evidence," said Bill Freese, Science Policy Analyst at Center for Food Safety.

EPA relied mostly on unpublished studies commissioned by the pesticide industry, 99% of which were negative; while IARC focused on the results of published, peer-reviewed studies, of which 70% produced positive findings of genotoxicity.

EPA's evaluation centered heavily on assays conducted with pure glyphosate, while IARC placed more weight on tests involving exposure to the actual glyphosate formulations used by farmers and homeowners, which contain additional ingredients. Glyphosate formulations are widely considered more toxic than glyphosate alone.

Finally, EPA's evaluation focused on typical dietary exposure of the general population assuming legal applications on food crops, and did not consider the much higher exposure levels common among farmers, groundskeepers, and applicators applying GBHs for many days per year as part of their jobs. IARC's assessment, on the other hand, encompassed data reflecting dietary and occupational use, as well as exposure from living in or near heavily sprayed areas.

IARC's assessment that glyphosate is probably carcinogenic rests on other evidence as well: three epidemiology studies that showed elevated rates of non-Hodgkins lymphoma in glyphosate-using farmers, and multiple studies in which rodents fed glyphosate developed tumors.


The study comes as thousands of cancer victims have sued Monsanto, which was acquired by Bayer CropScience in 2018, alleging that exposure to Roundup was responsible for their non-Hodgkin lymphoma (NHL). In August 2018, a California jury found in favor of a school groundskeeper who regularly used Roundup and has a terminal case of NHL. The jury unanimously found that Monsanto had failed to warn of the cancer-causing dangers of its brand-name Roundup herbicides and related products, and awarded the groundskeeper $289 million in damages, later reduced to $78 million. Several similar lawsuits are scheduled for 2019.

Monsanto and the EPA have come under heavy fire regarding glyphosate. Documents revealed in the course of cancer litigation have shown that Monsanto officials "ghost-wrote" studies published by supposedly independent scientists in an effort to downplay the evidence of glyphosate's carcinogenicity. E-mails between an EPA scientist and a Monsanto officer suggest coordinated efforts to undermine the legitimacy of IARC's "probably carcinogenic" determination for glyphosate in advance of its official release.

At the behest of CropLife America, a pesticide industry lobby group that includes Monsanto, EPA removed an eminently qualified government scientist it had itself appointed to a Scientific Advisory Panel charged with evaluating glyphosate's carcinogenic potential in 2016.

EPA admits that its genotoxicity and animal study evaluations apply only to pure glyphosate, and says it is working with other government scientists from the National Toxicology Program to assess the toxicity of glyphosate formulations. However, these efforts could be hampered by EPA's apparent ignorance of what precisely some Roundup formulations contain.

At the start of a comprehensive review of glyphosate in 2009, EPA scientists admitted they did not know the identity of some ingredients (e.g. surfactants) in glyphosate formulations or the toxicity of many of them (see p. 31). EPA was scrambling to obtain this information from Monsanto as late as 2016. Pesticide companies are required by law to report these formulation additives to EPA, yet are allowed to hide their identities from the public and scientists as "trade secrets," so it is unclear why EPA does not already have this fundamental information.

The newly published study is being submitted to the EPA so the Agency will have the opportunity to revisit the full body of evidence on Roundup and GBH genotoxicity compiled by IARC prior to completing its registration review of the herbicide. The study also reports on 27 GBH genotoxicity studies published in scientific journals since EPA's last formal review of the cancer data, 26 of which reported a positive genotoxic responseâ??data that EPA will also be able to consider before issuing its final registration decision.

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