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Review Finds 87% of Glyphosate Studies Since 2016 Reported Genotoxic Response


Brief Summary: Experts in Monsanto Roundup lawsuit cases published a review paper that analyzed glyphosate studies since 2016. According to the research 84 glyphosate studies reported a genotoxic response compared to just six that did not find a positive response.

Despite massive jury verdicts against Monsanto and settlement agreements with Bayer (which acquired Monsanto in 2018), glyphosate, a key ingredient in Roundup weed killer, remains one of the most heavily applied agrochemicals. One of the reasons for its continued use is the U.S. Environment Protection Agency’s conclusion that glyphosate is not likely to cause cancer.

The authors of a review published earlier this year say EPA’s conclusion is “untenable,” given the growing body of research that has found increased risk for cancer associated with glyphosate exposure. According to the authors, over the last seven years, 84 newly published studies reported a genotoxic response following exposure to glyphosate or a glyphosate-based herbicide (GBH) compared to just six published studies that reported no evidence of such a response.

EPA is currently conducting a reevaluation of glyphosate to ensure there are no unreasonable adverse effects on human health or the environment. As discussed in the blog below, it seems clear that new evidence should force the agency to change its conclusion. But after decades of towing the line for major corporations like Monsanto, we will have to wait and see.

Roundup Lawsuits Highlight Cancer Pathways

Most people who use Roundup do so on a small scale, meaning they pick up Roundup Weed & Grass Killer at Home Depot and spray the product in their yards (this will soon change after Bayer announced it will stop selling Roundup to residential consumers in 2023 due to pressure from the verdicts and over 100,000 injury claims against the company). Small, handheld sprayers and other equipment can potentially lead to high levels of dermal exposure and absorption.

The question of whether this exposure can cause cancer is something that has been argued in courts throughout the country over the last five years and counting. In the beginning of the litigation, three different juries overwhelmingly agreed that Roundup caused the plaintiffs to develop non-Hodgkin’s lymphoma (NHL). Each of the first three cases cleared the appeals process, albeit with reduced verdicts, and none were taken up by the U.S. Supreme Court.

Our firm co-led two of these cases and served on the trial team in all three. We take great pride in the fact that we were able to clearly show the juries the science linking Roundup and cancer. These cases paved the way for an $11 billion agreement between our firm and several others on behalf of thousands of clients.

The trials that followed the first three have all gone the way of the defendant. The heart of the debate has been the same since the start of the litigation: there is a significant difference between how Monsanto/Bayer and the U.S. Environmental Protection Agency (EPA) evaluated glyphosate’s carcinogenic potential versus how the International Agency for Research on Cancer (IARC) and independent scientists worldwide evaluated glyphosate’s carcinogenicity.

Why EPA and IARC Came to Different Conclusions on Glyphosate

In 1985, the EPA examined data from Monsanto to evaluate glyphosate’s toxicity. After evaluating Monsanto’s own studies, a group of EPA scientists determined that glyphosate was carcinogenic, or a ​“Class C” substance. However, their conclusions would eventually be reversed by EPA upper management and advisory boards after pressure from Monsanto (as alleged in lawsuits).

In 1991, EPA announced that glyphosate would change from a ​“Class D” substance (not classifiable) to a ​“Class E” (evidence of non-carcinogenicity for humans based on the lack of convincing evidence in adequate studies). The matter of glyphosate’s carcinogenicity remained the same until 2015 when IARC classified glyphosate as “probably carcinogenic” to humans.

Here are a few key reasons why EPA and IARC differ on glyphosate:

  • There is significant potential for glyphosate-based herbicide (GBH) genotoxicity caused by coformulants (other non-active additives), coupled with the enhancement of dermal penetration brought about by the most common GBH surfactants. GBH applicators are exposed to far more glyphosate in a day of spraying GBHs than from glyphosate residues in their diet. This is especially the case among small scale applicators who apply a GBH with handheld spray equipment.
  • EPA focused its review primarily on dietary exposure to technical glyphosate (oral route of exposure) while largely ignoring dermal exposure to GBHs. Surfactants in GBHs can increase dermal exposure for applicators, thus increasing the risk of developing cancer.
  • EPA focused on studies testing technical glyphosate in isolation, which is different than GBH products like Roundup, which contains glyphosate, surfactants, and other additives. IARC, on the other hand, placed considerable weight on in vivo studies of GBH’s and focused on biomarkers of genotoxicity in exposed human populations and experimental animals.
  • EPA relied predominantly on studies conducted by or for GBH registrants like Monsanto, almost all of which were negative. IARC relied on a larger body of mostly published genotoxicity studies, especially those involving people exposed to GBHs for years. Over 70% of the genotoxicity studies that IARC reviewed reported one or more positive response. EPA placed little or no weight on these key studies.

Glyphosate Cancer Link Controversy

In the 1990s, researchers published the first study to conclude glyphosate-based herbicides (or GBH’s) can damage DNA. Genomic instability is one of the most important factors that can lead to the development of cancer. At the time the research was published, Monsanto, which brought GBH’s to market in 1974, had submitted dozens of genotoxicity studies, nearly all of which did not find positive responses. Monsanto’s glyphosate research, combined with the company’s efforts to rebut outside research, convinced regulators that the chemical was not a carcinogen.

Read More About Monsanto’s Controversial 1983 Mouse Study

Between 2000 and 2010, scientists found more positive associations between glyphosate and genotoxicity. Since then, the majority of research has found a positive genotoxic response from glyphosate or GBH exposure.

Yet despite the new evidence linking GBH’s like Roundup and DNA damage (via multiple mechanisms of action), EPA and other regulatory bodies throughout the world have not changed their stance on glyphosate carcinogenicity. But change may happen soon: Last year, the Federal Circuit Court of Appeals vacated EPA’s assessment of glyphosate human-health risks, requiring the agency to revisit old data and take into account new data in its glyphosate reregistration decision.

New Glyphosate Review: Most Modern Research Positive for Genotoxicity

In January of 2023, the journal Agrochemicals published a review titled, Genotoxicity Assays Published since 2016 Shed New Light on the Oncogenic Potential of Glyphosate-Based Herbicides.”The study authors include Charles Benbrook, Robin Mesnage, and William Sawyer. Benbrook and Sawyer served as expert witnesses in legal cases against Monsanto/Bayer alleging exposure to Roundup weed killer causes non-Hodgkin’s lymphoma (NHL).

According to the researchers, over the last seven years, 84 new glyphosate studies reported a genotoxic response following exposure to glyphosate or a GBH compared to just six published studies that reported no evidence of such a response.

“We conclude that the 80+ positive glyphosate/GBH genotoxicity assays published since 2016 provide clear and compelling evidence that both glyphosate and formulated GBHs are genotoxic. We also find that the POEA surfactants in many GBHs markedly increase genotoxic potency in contrast to glyphosate alone. Hence, the assertion of no credible data supporting the genotoxicity of GBHs is erroneous and no longer tenable.”

The review authors also proposed some important statutory changes relevant to the assessment of GBH oncogenicity, including:

  1. The identity and concentrations of all inert ingredients should be disclosed and listed on pesticide labels.
  2. Applicator and farmworker dermal-exposure risk assessments should be markedly improved and new risk-mitigation measures and requirements codified in law.
  3. The majority of the toxicological and exposure studies required by EPA prior to approval of new pesticide uses, or reregistration of existing uses, should be carried out on both active ingredients and selected, widely-sold formulated products.
  4. Most foundational pesticide toxicity and risk assessment studies should be conducted by scientists independent of the pesticide industry.

The review noted the contributions of Wisner Baum (formerly Baum Hedlund), specifically our firm’s role in releasing discovery documents now known throughout the world as “The Monsanto Papers.” Thanks to the Monsanto Roundup litigation, scientists, regulators, journalists, and the public got to see a large number of internal pesticide-manufacturer studies, regulatory submissions, company emails, and planning and regulatory-response documents. “Collectively, these documents provide a historical accounting of what Monsanto understood about Roundup toxicity and risks since first approval in 1974,” the authors write.

Wisner Baum Injury Attorneys: EPA Needs to Change Regulatory Stance on Glyphosate

It is our hope that EPA takes into account the growing body of new research linking glyphosate and cancer. We believe the agency is long overdue in changing its regulatory stance on glyphosate to clearly inform consumers that GBHs like Roundup can cause cancer. Over 80,000 people are newly diagnosed with non-Hodgkin’s lymphoma each year. Some of those are likely to be among the millions of people who regularly spray Roundup at home, in gardens, at schools, on highways, or countless other places.

It is time for EPA to live up to its mandate and protect people and the environment from a known toxin.

Wisner Baum injury attorneys are no longer taking on Roundup lawsuits. Nothing in this blog is intended to promote or encourage further litigation against Monsanto related to Roundup and NHL.



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