Law and Science in Glyphosate Litigation

A consolidated personal injury lawsuit with approximately 280 individuals claiming exposure to Monsanto Company’s glyphosate based formulations (GBFs) caused non-Hodgkin lymphoma (NHL) is scheduled for Daubert hearings (1) during March of 2018. During these hearings, U.S. District Court Judge Vince Chhabria will apply the “more probable than not” Daubert standard to the reports, depositions and testimony of experts and correspondingly limit the studies qualifying for inclusion within the jury trial.

The Daubert standard requires an assessment of scientific validity by Judge Chhabria of studies by the experts of the Plaintiffs and Monsanto within adversarial hearings which include highly technical evidence from expert reports, depositions and verbal examinations. Judges can consider this task quite intimidating:

Reference Manual on Scientific Evidence, 2011

Lawyers often refer to the measures of scientific validity as the Bradford Hill “criteria” referring to Sir Austin Bradford Hill’s lecture in 1965 regarding environment and disease with references to nine factors, viewpoints or judgments which could affect the validity of causation. In practice, judges refer to the Reference Manual on Scientific Evidence (Third Edition, 2011) published by the Federal Judicial Center and the National Research Council and updated periodically to reflect the evolution of scientific and analytical techniques:

International Agency for Research on Cancer

The Plaintiffs are attempting to position the International Agency for Research on Cancer (IARC) Monograph 112 as a valid omnibus study for the Daubert hearings. However, the hazard based IARC conclusion with wording such as “limited evidence for the carcinogenicity of glyphosate in humans” and “cannot rule out chance, bias or confounding” is starkly different than the “the more probable than not” Daubert standard. The Plaintiffs’ position also does not consider the individual validity of IARC studies with novel interpretations, weightings and analysis or studies published subsequently which are contrary to the IARC conclusions.

Epidemiological Studies

The nature of the case requires proving exposure to glyphosate causes NHL in humans, a consideration which has led both sides to recognize the importance of epidemiological studies.

The recently updated and enhanced Agricultural Health Study (AHS) was placed into the list of epidemiological studies for evaluation during the Daubert hearings by Court Order over the objections of the Plaintiffs. A Monsanto brief summarized the AHS as follows:

The Plaintiffs claim the validity of the AHS is impaired by the method of imputing data for non-responding farm applicators and the failure to recognize the dramatically increased use of glyphosate in recent years. The imputation technique as documented by the Heltshe et al. 2012 publication claims it is the most accurate method for reducing bias and deriving increased precision for missing data from survey non responders for each of the successive surveys performed. The validity of the technique is also confirmed by sensitivity analysis within the AHS methodology.

There are also other epidemiological studies which could be debated during the Dauber hearings. The De Roos 2003 study has been proposed by the Plaintiffs, but there are statistical issues which likely impair study results. The De Roos 2005 study controls for other pesticide exposures, but the resultant null finding for glyphosate (self-reported, not proxy reported) and NHL does not support the Plaintiffs. The Plaintiffs’ expert noted that within the Eriksson 2008 study , it is “impossible to tell if risk (is) elevated because of failure to control for other pesticides”. The unadjusted McDuffie 2001 and Hardell 2002 studies reflect increased NHL risks for glyphosate, but these risks are significantly reduced when fully adjusted to reflect other pesticides.

Human Biomonitoring

Human biomonitoring studies related to the aerial spraying of coco plantations in Ecuador and Colombia have been identified by Plaintiffs’ experts as studies reflecting causation. However, the Paz-y-Mino 2007 and 2011 studies in Ecuador were evaluated as follows within Kier’s review (2015) of genotoxicity biomonitoring for GBFs studies:

The Bolognesi 2009 study in Colombia was also summarized within Kier’s review:

In addition, the following excerpt is from a letter to the IARC with two of the Bolognesi study authors objecting to the erroneous interpretations and conclusions:

Animal & Mechanistic Studies

Plaintiffs have identified toxicology studies as a means to identify plausible biological mechanisms.The Greim et al. 2015 study used a number of proprietary company animal regulatory tests of the European Union which were subsequently publicized and publicly available for three months at a Brussels Reading Room. Plaintiffs have objected that Monsanto’s expert veterinary pathologist reviewed the studies of Greim in the reading room without notifying them, but regardless of the objection, the Greim study indicates glyphosate poses no carcinogenic potential for humans as summarized in the abstract:

An evaluation of mechanistic related evaluation is provided by the Kier & Kirtland 2013 review of publications and regulatory studies regarding in vitro gene mutation or chromosomal effects. The abstract reflects unfavorable conclusions for the Plaintiffs:

Predicted Judicial Results

The responsibility for establishing scientifically valid proofs with a relative risk of more than 2.0 rests solely with the Plaintiffs and only those qualifying studies or groups of studies may be used within the jury trial. An absence of qualifying studies requires a summary judgment in favor of Monsanto.

Absent valid epidemiological studies showing more than a 2.0 relative risk for NHL and the powerful AHS null finding, Judge Chhabria will not have a basis for moving into the trial phase. The Plaintiffs’ unique interpretations of the human biomonitoring studies extend beyond the documented studies and also fail to provide evidence of causation for NHL. Toxicology studies proposed by the plaintiff, if validated, could only be used in support of a validated and positive epidemiologic finding.

An expensive and time consuming consequence of the Daubert hearings may be the realization an adversarial hearing of experts can identify weaknesses in methodologies and conclusions better than present alternatives, particularly as related to the “closed” IARC Monograph program.

(1) More information regarding the Daubert standard was published in Daubert Standards Present Formidable Hurdle in Glyphosate Litigation.



Analyst and 30 year Costa Rican resident

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