In 2015, a working group convened by the WHO’s International Agency for Research on Cancer (IARC) conducted a hazard assessment focusing on the carcinogenicity of glyphosate.  It concluded that glyphosate, historically considered to be a very safe pesticide, was a probable human carcinogen.  This prompted the WHO through its Joint Meeting on Pesticide Residues (JMPR) to conduct a re-assessment of the risks of glyphosate as a pesticide residue, which after reviewing the human, animal and mechanistic evidence, led to the conclusion that glyphosate residues in the diet were unlikely to pose a cancer risk.  In this presentation, I will overview the JMPR’s evaluation of the genotoxicity and animal carcinogenicity studies of glyphosate.  Hundreds of genotoxicity studies on glyphosate and its formulation products were reviewed, and an unusual pattern of results has been observed.  No increase in mutations was seen in the vast majority of bacterial test systems.  However, DNA damage and chromosomal effects were frequently seen in cell culture models and in organisms that are phylogenetically distant from humans (e.g. plants, earthworms, frogs, fish, caiman, etc.).  In contrast, in a large number of tests in mammalian models orally administered glyphosate, no increase in genotoxicity was seen.  Similarly, glyphosate has been tested in a substantial number of animal cancer bioassays.  While occasionally increases in tumors have been seen in various tissues, in most cases, these were not seen in other studies, often those in which higher doses were administered.  The JMPR concluded that there was no consistent increase in the rat studies but that a clear conclusion could not be reached for some of the mouse studies.  However, the doses at which the potentially positive effects were seen were extremely high, and were considered not to be relevant to humans exposed to low levels in the diet.

Evaluating the genotoxicity and animal carcinogenicity of glyphosate and their relevance to humans exposed to pesticide residues

ACS Fall 2020 Virtual Meeting

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