SHELDON KRIMSKY, PhD: Glyphosate on Trial: The Search for Toxicological Truth

In 2015, the International Agency for Research on Cancer (IARC), an inde­pendent research group under the auspices of the World Health Organiza­tion, issued its toxicological evaluation of the herbicide glyphosate. IARC concluded: “Glyphosate is probably carcinogenic to humans.” The release of its report created a firestorm of activity throughout the world. Glyphosate is the most widely used herbicide on the planet. Since it first came into use in 1974, it has been evaluated many times by a number of governmental bod­ies including the U.S. Environmental Protection Agency (EPA), the Euro­pean Union, and the European Food Safety Authority (EFSA), where it was found safe for human use with no strong evidence that it was a probable human carcinogen.

Monsanto, manufacturer of one formulation of glyphosate called Roundup™, sold both for farm and domestic use, took aggressive action against the findings of the new study by funding counter studies, reviews, data reanalysis, lawsuits, and media campaigns to protect its product from IARC’s negative report. On March 28, 2017, California’s Office of Envi­ronmental Health Hazard Assessment (OEHHA) announced it was add­ing Roundup as well as other glyphosate-based weed killers to the state’s Proposition 65 list of cancer-causing chemicals. In a letter to Monsanto, OEHHA wrote, “Proposition 65 required the listing of certain chemicals and substances” when found to be cancer causing agents. “Under the stat­ute, case law and regulations, chemicals identified by IARC as carcinogens with sufficient evidence of carcinogenicity in humans or animals must be listed under Proposition 65.”

Under the law, California was not required to, nor did it, do additional testing or risk analysis. Monsanto challenged OEHHA’s listing; its challenge was defeated at the trial court and was appealed. If the final judicial approval is given for the glyphosate listing, companies will have to label the glyphosate-based weed killer as a “probable human carcinogen.” On April 19, 2018, a California Appellate Court ruled that Monsanto’s glyphosate herbicide can be labeled as a probable human carcinogen under Proposition 65.

Meanwhile, the toxicology of glyphosate is being debated within the scientific community. The goal of this chapter is to examine the different interpretations of the scientific literature on the health and safety of glypho­sate and its formulations among herbicides. Why does one World Health Organization agency reach a decision that glyphosate is a probable human carcinogen while others, including the EPA, conclude, with equal confi­dence, that it is not a human carcinogen? How should consumers respond?

Before I answer these questions, I begin with the backstory—the story not found in the scientific literature but that can have a profound effect on it. . . . .

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