SAN FRANCISCO – Two expert witnesses who testified on behalf of plaintiffs suing Monsanto over claims a weed killer caused their cancer will be recalled to give further evidence.
The California judge in charge of the hundreds of consolidated cases taken by plaintiffs across the country may bar the cancer specialists giving evidence at trial that glyphosate, an active ingredient in Roundup weed killer, causes non-Hodgkin lymphoma (NHL).
U.S. District Judge Vince Chhabria of the U.S. District Court for the Northern District of California described the testimony of Dr. Beate Ritz and Dr. Christopher Portier as "shaky," according to a March article published by Agrow.
Their testimony contradicts a recent study by the National Cancer Institute (NCI), a government agency, and both go beyond the findings of the International Agency for Research on Cancer (IARC), which found glyphosate is "probably carcinogenic" but did not specify to what extent or identify any particular type.
Indeed, Chhabria advised the plaintiffs in the case that the IARC conclusion - itself criticized by Monsanto and others - is "not enough" to support causation, Agrow reported. The IARC is the World Health Organization's cancer research agency.
Laura Beane Freeman, a senior investigator at the NCI's division of epidemiology and genetics, said the institute's study found there was no statistically significant association between glyphosate use and cancer.
Freeman told the Northern California Record: "In our primary analyses, there was no statistically significant association between glyphosate use and cancer at any site, including non-Hodgkin lymphoma (NHL)."
Ritz, vice chair of the epidemiology department at the University of California, Los Angeles, and Portier are among a dozen experts the plaintiffs plan to call at trial. The hearing was held so the judge could decide whether the testimony and claims have sufficient weight to be heard by a jury.
"After reviewing all of the scientific literature at hand, I really concluded that, to a reasonable scientific degree of certainty, glyphosate and glyphosate-based compounds, including Roundup, do indeed cause NHL," Dr. Ritz told the court at a March 5 sitting, according to Agrow, an agribusiness publication.
Chhabria called that conclusion "dubious," and added, "There's at least a strong argument that the only reasonable conclusion one could draw right now is that we don't yet know," Agrow reported.
Portier testified, "To a reasonable degree of scientific certainty, given the human, animal, mechanistic evidence, glyphosate probably causes NHL, and the probability that glyphosate causes NHL is high," Agrow reported.
A former associate director at the National Institute of Environmental Health Sciences, a government agency under the auspices of the National Institute of Health, Portier is a high-profile voice internationally among those warning of links between the weed killer and cancer. He was an adviser to the IARC's working group that concluded it is probably carcinogenic.
A sometimes acrimonious debate has simmered for years over the claims that glyphosate does, or could, cause cancer.
While the IARC is standing by its conclusion, the NCI's Freeman told the Record: “We evaluated glyphosate exposure and cancer risk in the Agricultural Health Study (AHS), a cohort study of 57,310 pesticide applicators in Iowa and North Carolina who have been followed since the mid-1990s."
She said the finding of no association with NHL overall is consistent with a previous paper that was published in 2005.
"Additionally, we observed no association with any major NHL subtype; this is the first time these malignancies have been evaluated with respect to glyphosate exposure in the AHS," she said.
Freeman added, "We found some evidence suggesting an association with one subtype of leukemia, acute myeloid leukemia, particularly among applicators in the highest category of glyphosate exposure, compared to people who reported never using glyphosate.
"In addition to continued follow-up of this cohort to further investigate some cancer subtypes with a small number of cases, it will be important to study these associations in other populations.”
The IARC published the conclusion of its working group of experts in 2015, and since has faced criticism for the findings.
Most recently, it was accused in a Reuters article of ignoring papers that included findings contradicting the conclusion. The article compared a draft - obtained by Monsanto as part of the legal proceedings in California - to the final report.
In a lengthy rebuttal of the article, the IARC countered, "Most of these differences specifically relate to a review article co-authored by a Monsanto scientist."
It added, "The working group considered that the review article did not provide adequate information for independent evaluation of the conclusions reached by the Monsanto scientist and other authors; consequently, the draft was revised."
In a further statement, the IARC stated, "Following the classification of glyphosate....IARC has been the target of an unprecedented number of orchestrated actions by stakeholders seeking to undermine its credibility."
The IARC position is supported by the American Cancer Society.