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Posted by on in Centers of Excellence
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Popular pesticide classified as probable carcinogen by IARC

Posted on behalf of the author, Derek Drechsel


On March 20, 2015, the International Agency for Research on Cancer (IARC) issued a report on the carcinogenicity of five organophosphate pesticides, including the herbicide glyphosate. One of the most widely used herbicides in the world, glyphosate is the active ingredient in Roundup (Monsanto), and has been popularly used in recent years on crops that have been genetically engineered to be resistant to the herbicide.

The IARC report classifies glyphosate as 2A, “probably carcinogenic to humans,” based on “limited” evidence of carcinogenicity in humans and “sufficient” evidence in experimental animals. This classification is controversial, since glyphosate has long been considered one of the safest herbicides available with few usage restrictions, and other agencies including a recent German government evaluation on behalf of the European Union, have deemed glyphosate non-carcinogenic.

Several glyphosate exposure studies of agricultural workers conducted in the U.S., Canada, and Sweden reported an increased risk for non-Hodgkin’s lymphoma (De Roos, et al. 2003; McDuffie et al. 2001; Eriksson et al. 2008). However, the Agricultural Health Study, which is a collaborative effort involving investigators from the National Cancer Institute, the National Institute of Environmental Health Sciences, the Environmental Protection Agency (EPA), and the National Institute for Occupational Safety and Health, has followed pesticide applicators and farmers in the U.S. for over 20 years, with no findings of an increased risk of this cancer. The “probably carcinogenic” classification by IARC was based upon studies that demonstrated that glyphosate can cause cancer in laboratory animals, and caused DNA and chromosomal damage in human cells in vitro.

IARC’s report has also received considerable backlash from industry groups. Monsanto, which developed Roundup in the 1970s, and remains a top glyphosate producer, criticized the report stating that “relevant, scientific data was excluded from review.” In February, the German Federal Institute for Risk Assessment (BfR) completed an assessment of glyphosate, and, after reviewing hundreds of toxicology studies and nearly one thousand published reports, concluded that glyphosate had no “carcinogenic or mutagenic properties,” and is not “toxic to fertility, reproduction, or embryonal/fetal development in laboratory animals.” The BfR also reported that the toxicity of some glyphosate-containing herbicides is more likely due to other chemicals in the product formulation (such as surfactants), warranting additional research.

The actual task of determining the safety and potential risks associated with glyphosate and regulating its use in the U.S. falls to the EPA. In 1991, the EPA classified glyphosate as non-carcinogenic in humans, although the agency is currently conducting an updated review of several pesticides, including glyphosate, as part of a required periodic reevaluation cycle.

IARC will publish a full report later this year, with further details on its glyphosate assessment.


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