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Posted by on in Centers of Excellence
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IARC Continues Carcinogenic Classification of Commonly Used Pesticides

Posted on behalf of the author, Derek Drechsel


Previously, we discussed the decision of the International Agency for Research on Cancer (IARC) to designate one of the most widely used herbicides, glyphosate, as a Class 2A carcinogen, a designation which corresponds to “probably carcinogenic to humans”.

Similarly, IARC issued a report on the carcinogenicity of additional pesticides in June 2015. Following review of scientific literature, IARC classified the insecticide gamma-hexachlorocyclohexane (lindane) as a Class 1 carcinogen (i.e., “carcinogenic to humans”) and designated dichlorodiphenyltricholoroethane (DDT) as a Class 2A carcinogen (i.e., “probably carcinogenic to humans”). The use of these two insecticides was restricted or banned in many countries beginning in the 1970s following recognition of potential environmental and human health risks; nowadays, lindane is used for limited applications such as treatment of scabies, whereas DDT is only used for malaria control.

In addition, IARC classified 2,4-dicholorophenoxyacetic acid (2,4-D) as a Class 2B carcinogen (i.e., “possibly carcinogenic to humans”). This chemical has been used as an herbicide on a global scale for at least 40 years. IARC’s designation conflicts with the evaluations made by numerous entities throughout the world, including the U.S. Environmental Protection Agency (EPA), which designates 2,4-D as “not classifiable as to human carcinogenicity”. IARC concluded that the “limited evidence” for 2,4-D carcinogenicity from experimental animal models was adequate for the classification, while also acknowledging the existence of “inadequate evidence” in humans.

However, in light of the latest IARC reports, it is important to acknowledge that IARC’s process for evaluating the potential carcinogenicity of a given agent is distinct from the risk analyses used by most regulatory bodies. While evaluations of entities such as the U.S. EPA assess risk, or the probability that cancer will occur with chemical exposure, IARC’s classifications merely identify the possibility that a chemical can cause cancer. Therefore, a chemical designated as a carcinogen by IARC due to its possible effects does not indicate that it is likely to cause cancer in humans.

A full report from IARC on 2,4-D is expected later this year.

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