The internet has been awash in news related to glyphosate over the last few months. What is it all about? Well, that’s a bit of long story but I’ll provide an overview below.

Glyphosate is a broad-spectrum herbicide that was originally patented almost 50 years ago by Monsanto and marketed in their “Roundup” herbicide products. It became extremely popular for a range of agricultural uses, especially in conjunction with Monsanto’s “Roundup Ready” engineered crops that were resistant to the effects of the herbicide (i.e., Roundup could be sprayed on crops and only the weeds would be killed off). This ingredient came off patent in 2000, and since then many companies have been selling glyphosate-containing products in over 130 countries, becoming the most widely used herbicide globally.


As with any pesticide product, glyphosate (the active ingredient and formulated/finished products) was comprehensively reviewed for safety by government agencies prior to being permitted for use in North America, EU, etc. These were then re-evaluated in the last few years to ensure any new relevant safety data was captured.  Agencies like the Canadian Pest Management Regulatory Agency (PMRA), U.S. Environmental Protection Agency (US EPA), the European Food Safety Authority (EFSA)/European Chemicals Agency (ECHA), and the Australian Pesticides and Veterinary Medicines Authority (APVMA) have concluded that when used according to label instructions, glyphosate, and products that contain glyphosate, present a low toxicity hazard to humans and the environment. All of these agencies considered the potential for glyphosate to cause cancer in humans to be minimal, as robust evidence was lacking.


During this time, the International Agency on Cancer Research (IARC), a non-governmental agency within the World Health Organization (WHO), reviewed the potential for glyphosate to cause cancer in 2015 and concluded that there was sufficient evidence to categorize it as a Group 2A carcinogen (“probably carcinogenic to humans”). This was based on “sufficient” evidence in animals and  “limited” evidence for cancer in humans (note: IARC reported there was a positive association for non-Hodgkin’s lymphoma or NHL).


Interestingly, another group within the WHO, the Food and Agriculture Organization (FAO), concluded that glyphosate was unlikely to be carcinogenic to humans from dietary exposures.

Given the IARC classification, OEHHA was, by law*, required to list glyphosate on the Prop 65 list, which occurred on July 7th, 2017 with an NSRL of 1,100 ug/day derived based on a dietary cancer study in mice.


This caused a great deal of controversy regarding the differing conclusions, especially as claims surfaced that:

  • key scientific data that supported a lack of carcinogenicity was omitted in the review by IARC;
  • the use of published vs. unpublished data in different reviews;
  • whether the evaluation focused on glyphosate alone or on the final mixed product (which contains various surfactants that may impact safety);
  • the transparency of the processes; and
  • the potential for undo influence of industry in relation certain publications.

Although there have been many rebuttals on both sides addressing these concerns, the truth on these claims appears to remain….. somewhat muddled.  To delve into those details, would require a whole separate post. Overall, it appears that some of the issues relate to differing cancer classification criteria by different agencies and interpretations of the robustness of the studies when looked at from a weight-of-evidence approach. Generally, the overall evidence does NOT seem to support that there is actually a direct link between glyphosate exposure and NHL (for a great summary of the data, please see the post by Andrew Kniss here).


Regardless, after decades of use without major safety issues, one of Monsanto’s marquee products was classified as a carcinogen, which raised additional concerns regarding Prop 65 labeling requirements in California.  As such, Monsanto tried to petition OEHHA to reconsider the listing via the Labor Code mechanism (which failed), as well as take OEHHA to court on the grounds of free speech violations (i.e., forcing companies to put language on product labels that was not “uncontroversially” true). Clearly there appeared to be controversy surrounding whether glyphosate actually causes cancer in humans. Earlier this spring, a U.S. federal judge ruled in favor of Monsanto and temporarily blocked the need for labels in California to provide Prop 65 warnings for glyphosate. We will see if this remains the case; however, the NSRL provides an exposure threshold below which warnings are not required anyway.


The next flurry of headlines came mid-August after the conclusion of a landmark case in which a groundskeeper claimed that the use of Monsanto’s Roundup product for several years resulted in him getting non-Hodgkin’s lymphoma. He won and the jury awarded him a whopping $289-million in damages (which will be appealed).  Thousands of other plaintiffs are filing similar cases against Monsanto.


Finally, another flurry of headlines surfaced when the consumer-advocacy group, the Environmental Working Group (EWG) published a report in which it found that numerous breakfast cereals, contained detectable levels of glyphosate, some of which exceeded a safety threshold that was derived by EWG. It should be noted that government agencies set thresholds for residual pesticide levels in foods that take into account the intake of all foods that might contain a residue and are legally binding (these were not exceeded). EWG’s limit (not binding) seems to illustrate that they were looking to ensure they had headline-grabbing results (mission accomplished!).


Determining causal links between exposure to a substance and cancer is an extremely complex and difficult problem.  Cancers take many years to form and trying to either look backwards to possible causes or to track all possible risk factors is rife with confounding issues and potential for biases. All eyes will remain on glyphosate in the news as further trials proceed and potentially more research is conducted to further investigate the safety of glyphosate, especially the alleged link to cancer. This a fascinating topic and we’ll provide updates as new data or information are published.

*OEHHA is required to list any carcinogens that are classified by IARC as Group 1 or 2A carcinogens (per the “Labor Code Mechanism).

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