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Glyphosate and cancer: why is there a difference in its classification by the IARC and EFSA?

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Context - Glyphosate is a widely-used herbicide that was recently evaluated by the IARC and EFSA, which adopted different conclusions regarding its classification as a human carcinogen.

What explains such a difference in the classification of glyphosate between the evaluations conducted by IARC and EFSA?

This is a faithful synthesis and summary of several scientific consensus reports. For the full list of sources, refer to the references.

  • Source document:IARC / EFSA (2015)
  • Summary & Details: GreenFacts

Introduction

Recently, the herbicide glyphosate was evaluated for its potential human carcinogenicity by two agencies: the International Agency for Research of Cancer (IARC), associated with the World Health Organisation (WHO) and the European Food Safety Authority (EFSA) of the European Union.

While IARC classified glyphosate in class 2A “probably carcinogenic to humans”, EFSA did not consider it as representing a carcinogenic risk. This Highlight clarifies the origins and reasons of this difference, and puts them into perspective.

This difference in classification initiated a public debate among scientists and between the agencies. The present synthesis clarifies what these differences are and puts them into perspective.

In term of regulatory classification, what is the difference between « hazard » and « risk »?

In terms of regulatory classification, “hazard” refers to the intrinsic properties of an agent (physical, chemical, biological) – its capacity to cause harm - while “risk” takes also into consideration the probability and extent of exposure to the agent considered as hazardous.

This may result in different classifications depending on the integration or not of the risk as a factor for the classification.

A simple explanation of these concepts can be found in this GreenFacts video: https://www.youtube.com/watch?v=PZmNZi8bon8 

What is glyphosate and how is it used?

Glyphosate is the common name for N-(phosphonomethyl) glycine (IUPAC), a herbicide that is mostly known under one of its commercial brand ‘Roundup’, but is now also available on the market in a wide variety of other products, formulations and brands.

Glyphosate is generally used in spraying applications against emerged annual, perennial and biennial weeds in all crops. It can be used on soil but mainly on existing vegetation before planting fruit crops, ornamental plants, trees, nursery plants etc. It can also be sprayed on crops before the harvest to dry the leaves of cereals and oilseeds.

What was the basis for the IARC classification of glyphosate as « probably carcinogenic to humans »?

The Monographs by the International Agency for Research on Cancer (IARC) are based on the systematic assembly and review of all publicly available and pertinent studies by independent experts.

To reach its conclusion on glyphosate, IARC reviewed about 1000 studies and cited 269 in the Monograph, including experimental studies of both “pure” glyphosate and of glyphosate-based formulations. Globally, these studies reported similar and statistically significant increases in the same type of human cancer: non-Hodgkin lymphoma.

Based on experimental studies of “pure” glyphosate, the IARC Monograph1 concluded that the evidence for causing cancer in experimental animals was “sufficient’’ and the evidence for causing genotoxicity (damage to genes and/or chromosomes) was “strong”.

The Working Group reached the same conclusion for glyphosate and for its formulations regarding their hazard classification as “probably carcinogenic to humans”. IARC further stated that the probability of developing a cancer will depend on factors such as the type and extent of exposure and the strength of the effect of the agent.

What was the basis for the EFSA to not classify glyphosate as a human carcinogen?

The European Food Safety Authority (EFSA) evaluation process starts with a review of the available information by one of the member states, in this case Germany, followed by an extensive review process by all other member states and by the industry task force who supplied the initial assessment, as well as a public consultation. All of this documentation is available on the EFSA’s website.

In terms of carcinogenicity, the EFSA assessment focused on the pesticide active substance (and not its formulations) and considered all available information, including the IARC report2.

On the basis of the evaluation of the representative uses of glyphosate, the EFSA conclusions3 are that glyphosate is unlikely to pose a carcinogenic hazard to humans. The available evidence does not support classification with regard to its carcinogenic potential according to the European Regulation on classification, labelling and packaging of substances and mixtures. Based on the representative uses, that were limited to conventional crops only, chronic or acute risks for the consumers have not been identified.

EFSA considers that the genotoxic effects observed in some glyphosate-based formulations are related to other constituents or “co-formulants” and that, similarly, certain glyphosate-based formulations display higher toxicity than that of the active ingredient glyphosate. EFSA proposes thus that the toxicity of each pesticide formulation and in particular its genotoxic potential should be further considered.

Why is there a difference in classification, according to the agencies?

Regarding the criteria for classification, and as underlined by the agency itself, the IARC Monograph’s evaluation is a hazard classification. It indicates the strength of evidence that glyphosate can cause cancer. IARC further states that the probability of developing a cancer will depend on factors such as the type and extent of exposure and the strength of the effect of the agent.

According to EFSA4 , the main difference between the evaluations stems from the fact the IARC report looked at both glyphosate and the formulations that contain it, regardless of their composition. The assessment approach followed by EFSA, evaluates each individual chemical, and each marketed mixture separately, and therefore EFSA considered only the active substance glyphosate.

According to IARC5, many regulatory agencies rely primarily on industry data from toxicological studies that are not available in the public domain. In contrast, the IARC Working Group’s evaluation of glyphosate included all relevant evidence available in the public domain for independent scientific review, including any industry studies that met these criteria. IARC did not include data, which did not provide enough detail for appropriate assessment as was the case for some of the industry studies on cancer in experimental animals.

EFSA considers that, in total, they assessed more evidence than IARC including additional key studies.. EFSA will recommend to the European Commission to authorise its continued use as pesticide in the EU. However, EFSA underlined concerns regarding some information that is required by the regulatory framework but that was still missing.

Will these divergent conclusions and classifications on the carcinogenicity of glyphosate be resolved?

The World Health Organisation (WHO) has not yet formally accepted the conclusions of the IARC glyphosate Monograph and an extraordinary meeting on pesticides residues in May 2016 will address this issue6.

In an effort to clarify scientific divergences, EFSA, in line with its principles of openness and transparency, proposed to meet IARC early in 2016 to discuss the different evidence and the different methodologies that the two organisations have used.

Nevertheless, an exchange of letters between the Directors of both institutions indicated that this could not happen7.

References:
1  https://monographs.iarc.fr/ENG/Monographs/vol112/mono112-09.pdf
2 www.efsa.europa.eu/en/efsajournal/pub/4302 
3  www.efsa.europa.eu/sites/default/files/corporate_publications/files/efsaexplainsglyphosate151112en_1.pdf
4  www.efsa.europa.eu/sites/default/files/4302_glyphosate_complementary.pdf
5  www.iarc.fr/en/media-centre/iarcnews/pdf/Q&A_Glyphosate.pdf
6 www.who.int/foodsafety/areas_work/chemical-risks/call_for_data_for_2016_JMPR_May_final_1.pdf?ua=1 
7  www.esa.europa.eu/sites/default/files/Letter_from_Dr_Wild_to_Bernhard_Url_160212.pdf

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