The safety of the chemical has been under scientific and regulatory scrutiny since the 1980s. The U.S. Environmental Protection Agency and other international bodies, including the European Food Safety Authority, Health Canada’s Pest Management Regulatory Agency, New Zealand’s Environmental Protection Authority, and Japan’s Food Safety Commission, have kept it under regular review, and all say glyphosate is unlikely to cause cancer in humans.
But it is not settled science, and researchers across the world continue to study glyphosate—measuring traces of it in water and foods, exposing lab rats to it, and monitoring possible health effects in people who have used it year after year in their work.
One of the largest and most highly regarded studies to examine effects of pesticide use in real life is the Agricultural Health Study, a prospective investigation of about 89,000 agricultural workers, farmers and their families in Iowa and North Carolina. Since the early 1990s, it has gathered and analyzed detailed information on the health of participants and their families, and their use of pesticides, including glyphosate.
AHS researchers have published numerous studies from their data. One paper looking at glyphosate and possible links with cancers was published in 2005. It concluded that “glyphosate exposure was not associated with cancer incidence overall.” Since then, more data has been collected, adding statistical power to subsequent AHS analyses.
In early 2013, Blair and other researchers began preparing new papers with updated AHS data on lymphoma and pesticides, including data on glyphosate. Reuters reviewed drafts dated February 2013 and March 2013, and asked Spiegelhalter and Tarone to examine them. They said the papers, while still in the editing process, were in relatively advanced manuscript form. The drafts contain notes in the margin and suggested changes signed “AEB,” Blair’s full initials.
After studying the draft papers, Tarone said the unpublished figures show “absolutely no evidence whatsoever” of an increased risk of non-Hodgkin lymphoma because of exposure to glyphosate.
Spiegelhalter told Reuters: “In the drafts I saw, none of the herbicides, including glyphosate, showed any evidence of a relation” with non-Hodgkin lymphoma. He noted that the study was statistically strong enough to show a relationship for other pesticides—so had there been any link to glyphosate, it should have shown up.
In his legal testimony, Blair also described the Agricultural Health Study as “powerful” and agreed the data showed no link.
But these draft papers were never published, even though Blair told Monsanto’s lawyers in March that the Agricultural Health Study was robust and statistically well-powered, and told Reuters the research was important for science and the public. Email exchanges between Blair and his fellow researchers in 2014 also show they were keenly aware there would be scientific and public interest in fresh AHS data.
On Feb. 28, 2014, Michael Alavanja, a co-lead author of one of the draft papers, sent an email to another AHS co-researcher, copying the message to Blair. It noted that the research was “important to science, public health, IARC and EPA”—the U.S. Environmental Protection Agency.
In the same email, Alavanja referred to the findings on non-Hodgkin lymphoma, or NHL. He wrote: “It would be irresponsible if we didn’t seek publication of our NHL manuscript in time to influence IARCs (sic) decision.”
Yet the new AHS data on glyphosate and lymphoma did not surface.
Instead, a revised version of one of the 2013 draft papers prepared by Blair and other researchers appeared in a journal called PLoS One in October 2014. It did not include the data on herbicides, of which glyphosate is one.
This was unusual. Since 2003 AHS researchers had published at least 10 papers using different rounds of updated data to explore possible links between pesticides and specific diseases. And each one included all four pesticide classes: fungicides, fumigants, insecticides, and herbicides.