A Working Group of 17 experts from 11 countries met at the International Agency for Research on Cancer (IARC) on 3-10 March 2015 to review the available published scientific evidence and evaluate the carcinogenicity of five organophosphate insecticides and herbicides: diazinon, glyphosate, malathion, parathion, and tetrachlorvinphos.
Q&A on Glyphosate
In March 2015, IARC classified glyphosate as “probably carcinogenic to humans” (Group 2A).
This was based on “limited” evidence of cancer in humans (from real-world exposures that actually occurred) and “sufficient” evidence of cancer in experimental animals (from studies of “pure” glyphosate).
IARC also concluded that there was “strong” evidence for genotoxicity, both for “pure” glyphosate and for glyphosate formulations.
The IARC Monographs evaluation is based on the systematic assembly and review of all publicly available and pertinent studies, by independent experts, free from vested interests. It follows strict scientific criteria, and the classification system is recognized and used as a reference all around the world. This is because IARC evaluations are based on independent scientific review and rigorous criteria and procedures.
To reach these conclusions, IARC reviewed about 1000 studies. Some of the studies looked at people exposed through their jobs, such as farmers. Others were experimental studies on cancer and cancerrelated effects in experimental systems.
Could the carcinogenic effects of glyphosate be related to the other chemicals in the formulations?
Could the co-formulants be the cause of the genotoxic effects reported in the IARC Monograph?
Several of the epidemiological studies considered by the IARC expert Working Group showed increased cancer rates in occupational settings after exposure to glyphosate herbicides. Can this be attributed to glyphosate as a single ingredient or could it be due to other chemicals in the formulations?
One of the key studies evaluated in the Monograph was the United States Agricultural Health Study (AHS). This study did not find an association between non-Hodgkin lymphoma and glyphosate. Can this study alone outweigh the positive associations found in other epidemiological studies?
In the studies IARC evaluated, were there cancers only seen in animals exposed to the toxic doses of glyphosate?
Regulatory agencies have reviewed the key studies examined by IARC — and more — and concluded that glyphosate poses no unreasonable risks to humans. What did IARC do differently?
What does IARC′s classification mean in terms of the probability of developing a cancer?
Some Organophosphate Insecticides and Herbicides
Interview Kathryn Guyton, IARC Scientist, Acting Head, Monographs Group, Watch Video