IARC chairman explains glyphosate assessment: Real world circumstances not considered

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An international committee of cancer experts shocked the agribusiness world a few days ago when it announced that two widely used pesticides are “probably carcinogenic to humans.” The well-respected International Agency for Research on Cancer published a brief explanation of its conclusions in The Lancet and plans to issue a book-length version later this year.

The announcement set off a wave of feverish reaction, because one of these chemicals, glyphosate, is a pillar of large-scale farming. Better known by its trade name, Roundup, glyphosate is the most popular weedkiller in the world.

The IARC’s assessment leaves many questions unanswered, including how much risk glyphosate poses.

“What the IARC performs is hazard assessment,” says Aaron Blair, who chaired the group of scientists that prepared the IARC’s assessment of glyphosate. Blair is a scientist emeritus at the National Cancer Institute. Hazard assessment, he explains, is concerned with a simple question: Could a substance cause damage “in some circumstance, at some level of exposure?” How commonly such circumstances or exposures actually occur in the real world, he says, is an entirely different question, and not one that IARC tries to answer.

In other words, the IARC is saying that glyphosate probably could cause cancer in humans, but not that it probably does.

Blair points out that society often chooses simply to accept certain hazards. Among the other things that the IARC says probably cause cancer are burning wood in home fireplaces, disruption of circadian rhythms by working overnight shifts and working as a hairdresser.

Read full, original article: A Top Weedkiller Could Cause Cancer. Should We Be Scared?

  • Ivan R. Kennedy, Sydney

    As a professional in the chemistry of food safety, based on the chemical structure of glyphosate, I conclude that there is no likelihood that this highly specific herbicide is carcinogenic under real world conditions. A small molecule linking phosphate, amino and carboxylate groups of low physical impact with a chemical composition similar to many common cell metabolites, it acts as a herbicide only by virtue of specific competition with a similar substrate, preventing the normal formation of aromatic substances and wood in a biochemical reaction unknown in animals. Glyphosate is hardly more toxic than many other salty substances found in all organisms such as glutamic acid. Its structure shows no moieties or resonances considered as inducing cancer; any laboratory carcinogenicity occurs only at high concentrations with susceptible laboratory strains of rats or mice. Therefore, it is irresponsible of IARC to unreasonably cause such angst and waste of precious resources on the basis of the hazard assessment mentioned by Dr Blair so far removed from real risk. Given its lack of objectivity, this ruling of “probably carcinogenic in humans” without relevant evidence tarnishes the IARC’s reputation severely.