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EPA's flawed finding on Roundup and cancer

Emily Marquez's picture
Glyphosate spray

A new paper comparing the assessments of glyphosate’s carcinogenicity by the Environmental Protection Agency (EPA) and the International Agency for Research on Cancer (IARC) analyzed the kinds of studies used by both agencies — and found some glaring differences. Glyphosate is the active ingredient in Bayer’s (merged with Monsanto) widely used flagship herbicide Roundup.

If you’re not familiar with this story, IARC released its opinion on the active ingredient glyphosate in 2015, classifying glyphosate and glyphosate-based herbicides as “probably carcinogenic to humans.”

In 2016, EPA released its evaluation of the carcinogenicity of glyphosate and concluded that “the strongest support is for ‘not likely to be carcinogenic to humans’ at doses relevant for human health risk assessment.”

A difference in approach

The “relevant doses” EPA refers to are the glyphosate residues that the general population would be exposed to via food and beverage. But this is not the only way that glyphosate exposure happens.

The kinds of exposures and types of studies that agencies emphasize can greatly affect the outcome of an assessment. The paper concludes that EPA and IARC’s opposing conclusions were for three main reasons:

  • EPA focused on dietary exposures and didn’t address the higher exposures that occur in occupational scenarios, while IARC focused on elevated exposure scenarios.
  • EPA mostly relied on unpublished studies by the registrant (Monsanto), 99% of which concluded that there were no effects found. IARC relied on mainly peer-reviewed studies of which 70% observed an effect.
  • EPA evaluated data that mostly studied the single active ingredient glyphosate, while IARC weighted studies on the glyphosate-based herbicides, which include additional ingredients.

. . . and a difference in perspective

As indicated by the focus of IARC’s risk assessment, the agency’s approach is generally more precautionary than EPA’s.

For years, PAN has critiqued EPA’s approach of evaluating single active ingredients. This is especially problematic because pesticide formulations include many other ingredients that increase the toxicity (i.e., effectiveness) of the pesticide and thus may have an effect that you wouldn’t observe with just the single active ingredient.

In addition, EPA’s focus on typical exposures of the general population, which are dietary, doesn’t address the occupational exposure scenarios as seriously as it should. For instance, workers might use backpack-mounted sprayers to apply glyphosate and perfect use does not always occur. So, when there’s a leak, a worker’s clothing could be soaked with the chemical. High exposures can also occur during maintenance and repair of various types of sprayers.

Beyond occupational exposures, the author also points out that children can be exposed to higher amounts of glyphosate. For example, a child could be playing with a dog that has recently been in an area sprayed with glyphosate-based herbicide.

“Debate likely to persist”

As the paper discusses, the debate over the carcinogenicity of glyphosate-based herbicides is “ongoing.” In the meantime, we’re using an awful lot of this herbicide, it has been losing its efficacy, and it looks like it could be carcinogenic. Does that make sense to you? Because it sure doesn’t to me.

It is ridiculous to even consider EPA’s “not likely to be carcinogenic” conclusion when it’s human health and cancer we’re dealing with. Especially since the EPA’s risk assessment relies heavily on data coming from the pesticide industry itself.

Emily Marquez
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Emily Marquez is PAN's Staff Scientist. She is a biologist with a background in endocrine disruption and environmental toxicology in reptiles. In addition to supporting scientific research for PAN’s campaigns, Emily trains community members in using PAN’s Drift Catcher to monitor for pesticide drift. Follow @EmilyAtPan