New study: Glyphosate not carcinogenic

WASHINGTON, Sept. 28, 2016 - Glyphosate, the active ingredient in Roundup weedkiller and the most widely used herbicide in the world, “is unlikely to pose a carcinogenic risk to humans,” a new study by a panel of scientists has found. Glyphosate manufacturer Monsanto commissioned the study from Intertek Scientific & Regulatory Consultancy in Canada, which assembled the 15-member panel.

Monsanto undertook the effort to respond to a 2015 report from the World Health Organization's International Agency for Research on Cancer (IARC) that found glyphosate probably causes cancer in humans.

IARC said it came to that conclusion based on “limited evidence of carcinogenicity in humans for non-Hodgkin lymphoma” and “convincing evidence that glyphosate also can cause cancer in laboratory animals.”

The new study, published online today in the journal Critical Reviews in Toxicology, is the latest to tackle the question of glyphosate's carcinogenic potential. A report released by EPA Sept. 16 in anticipation of a Scientific Advisory Panel meeting next month on the subject reached conclusions similar to those in the Monsanto-funded study.

Said Monsanto: “These findings by the panel come at an important time, after so much unnecessary confusion and concern has been caused by IARC's classification of glyphosate.

The panel's findings are consistent with the conclusions of regulatory authorities around the world. In fact, since IARC classified glyphosate, regulatory authorities in the United States, Europe, Canada, Japan, New Zealand and Australia have publicly reaffirmed that glyphosate does not cause cancer.”

Nathan Donley, a scientist with the Center for Biological Diversity, said the latest study offered “nothing new” beyond EPA's previously released report. He said it was “no surprise (that) a Monsanto-funded study found that glyphosate does not cause cancer.”

Eight of the 15 authors served as independent consultants for Monsanto on the European Glyphosate Task Force, and two others have been employed by Monsanto and served as consultants. The paper contains a detailed “declaration of interest,” and a table posted when the preliminary results were released contains additional information on the panelists.

The Intertek authors noted the differences between their process and IARC's.

“IARC reviews and assesses … data in the context of hazard (i.e. inherent carcinogenic potential), not risk (i.e. the likelihood of carcinogenic effects at exposure levels humans may encounter). As a result, the conclusion of IARC is often solely associated with hazard.”

In addition, “IARC only reviews data included in: ‘reports that have been published or accepted for publication in the openly available scientific literature' or ‘data from governmental reports that are publicly available'” the study said, quoting IARC's own procedures.

The 15 scientists assembled by Intertek organized themselves into four panels covering toxicology, mechanism, exposure and epidemiology. The first three of those “evaluated all of the available scientific data, including the results of a number of unpublished reports, some of which have been submitted to and reviewed by regulatory authorities,” the paper said.

Donley criticized the use of unpublished data. “When the bulk of your analysis involves unpublished studies that have been hidden from the public, then anyone should be skeptical,” he said. “IARC has been the gold standard for research on cancer for the last 50 years. IARC's is the only analysis done so far that has only taken into account publicly available data that you and I can access. As far as I'm concerned, if industry feels that their research should be analyzed, they need to make their studies available to the public.”

The Intertek authors, however, defended their use of unpublished data, which have been summarized in publicly available tables. They specifically cited tables compiled by Larry D. Kier and David J. Kirkland, who both served on the Intertek panel.

“The rationale supporting the inclusion of these additional studies is that the supplementary tables presented in the Kier and Kirkland paper contain sufficient detail supporting the reliability of the studies,” the paper said. “Failure to evaluate and consider the large number of results included in the publication by Kier and Kirkland, as well as other publicly available studies not reviewed by IARC, results in an inaccurate assessment” of glyphosate's potential genotoxicity.

IARC concluded that there was “strong evidence that glyphosate causes genotoxicity,” but the Intertek panel's weight-of-evidence assessment “provides strong support for a lack of genotoxicity, particularly in the relevant mechanism categories (mutation, chromosomal effects) associated with carcinogen prediction,” according to the paper.

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