Nature analyzes the new World Health Organization (WHO) determination that Roundup weedkiller causes cancer:
The cancer-research arm of the World Health Organization last week announced that glyphosate, the world’s most widely used herbicide, is probably carcinogenic to humans. But the assessment, by the International Agency for Research on Cancer (IARC) in Lyon, France, has been followed by an immediate backlash from industry groups.
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On 20 March, a panel of international experts convened by the agency reported the findings of a review of five agricultural chemicals in a class known as organophosphates. A summary of the study was published in The Lancet Oncology.
Two of the pesticides — tetrachlorvinphos and parathion — were rated as “possibly carcinogenic to humans”, or category 2B. Three — malathion, diazinon and glyphosate — were rated as “probably carcinogenic to humans”, labelled category 2A.
Why should I care about glyphosate?
Glyphosate is the world’s most widely produced herbicide, by volume. It is used extensively in agriculture and is also found in garden products in many countries. The chemical is an ingredient in Monsanto’s weedkiller product Roundup, and glyphosate has become more popular with the increasing market share of crops that are genetically engineered to be tolerant to the herbicide.
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Although several studies have shown that people who work with the herbicide seem to be at increased risk of a cancer type called non-Hodgkin lymphoma, the report notes that a separate huge US study, the Agricultural Health Study, found no link to non-Hodgkin lymphomas. That study followed thousands of farmers and looked at whether they had increased risk of cancer.
But other evidence, including from animal studies, led the IARC to its ‘probably carcinogenic’ classification. Glyphosate has been linked to tumours in mice and rats — and there is also what the IARC classifies as ‘mechanistic evidence’, such as DNA damage to human cells from exposure to glyphosate.
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Doesn’t just about everything cause cancer if you look hard enough?
The IARC classifies compounds on a scale of decreasing certainty: group 1 is for agents that are definitely carcinogenic to humans; 2A, probably carcinogenic to humans; 2B, possibly carcinogenic to humans; 3, not classifiable; and 4, probably not carcinogenic to humans.
Monsanto said in its statement, “IARC has classified numerous everyday items in Category 2 including coffee, cell phones, aloe vera extract and pickled vegetables, as well as professions such as a barber and fry cook.”
But the IARC classified most of these items at the less dangerous 2B level, whereas glyphosate is in the ‘probably carcinogenic’ 2A category. Of Monsanto’s list, only emissions from high-temperature frying and the occupational exposure experienced as a barber are rated as 2A.
Food for thought.