In March 2015, the UN International Agency for Research on Cancer set off a scientific and regulatory row when it declared that glyphosate, the main ingredient in Roundup herbicide, is “probably carcinogenic to humans.” The EPA reached the opposite conclusion in late 2017, that glyphosate is “not likely to be carcinogenic to humans.” A paper appearing in a scientific journal on Monday said the IARC and EPA looked at different materials in reaching contradictory decisions.
An editorial in the journal, Environmental Sciences Europe, says the paper “provides new insights on why different conclusions…were reached.” The EPA and IARC “focused on two different but interlinked scenarios: 1, the exposure to (pure) glyphosate, which occurs via residues in food and feed and is therefore mainly relevant for the general public, and 2, occupational exposure, which is a multi-pathway exposure to the formulated glyphosate-based herbicide. Both scenarios are relevant.”
The author of the paper, Charles Benbrook, a visiting professor at the University of Newcastle, said the IARC relied on published studies; gave weight to research on so-called formulated herbicides, which are the weedkillers in use; and considered dietary, occupational and high-exposure scenarios. By contrast, the EPA considered unpublished reviews that chemical companies submitted to regulators as well as peer-reviewed studies of glyphosate in its pure chemical form and focused on likely dietary exposure to the chemical by the general public. The IARC found far more studies with a carcinogenic link. In addition, the EPA and IARC cited different sets of genotoxicity assays; those cited by the IARC generally showed a cancer link while the EPA list did not.
“IARC’s evaluation relied heavily on studies capable of shedding light on the distribution of real-world exposures and genotoxicity risk in exposed human populations while EPA’s evaluation placed little or no weight on such evidence,” wrote Benbrook. The EPA is somewhat circumscribed by laws and policies to look at the risk to the public and environment from pesticides that are used according to label directions, he said. Research and risk assessments, as well as the debate over glyphosate “should be focused on studies relevant to the biological impacts triggered by exposures to widely used, formulated GBHs (glyphosate-based herbicides).” Some studies say the formulated herbicides are more toxic than glyphosate in its pure form.
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