The International Agency for Research on Cancer started a global debate by rating glyphosate, the most widely used weedkiller in the world, as “probably carcinogenic to humans” while the EPA says its studies indicate it is “not likely to be carcinogenic to humans at doses relevant to human health.” Harvest Public Media says the difference in view is partially explained by the way the agencies chose to evaluate the issue.
EPA wants to know if glyphosate is likely to cause cancer at normal exposure levels. The IARC judges whether it is possible to cause cancer, including at high doses. (The IARC says it evaluates cancer hazards but not the risk — the probability of cancer — associated with exposure; recognition of carcinogenic hazards are important, it says, “because new uses or unforeseen exposures could lead to risks that are much higher” than current estimates.)
“Another difference is that IARC only looks at studies published in scientific journals in an attempt to avoid conflicts of interest. IARC considered hundreds of studies, but left out research done by the chemical industry,” says Harvest Media. Monsanto, which popularized glyphosate under the brand name Roundup, says IARC excluded studies performed by industry scientists but under guidelines set by regulators. Monsanto says safety reviews in other countries jibe with EPA’s conclusions about glyphosate’s safety.
The EPA says it would like more studies on human exposure to glyphosate. “But those are difficult,” says Harvest Media, because of the long timespan needed for the research. The EPA also wants to know if different formulations of glyphosate, in which various chemicals are added in order to make the weedkiller more effective, have a different health impact than glyphosate on its own.