Recently, the herbicide glyphosate was
evaluated for its potential human carcinogenicity by two agencies: the
International Agency for Research of
(IARC), associated with the World
Health Organisation (WHO) and the European Food Safety Authority
(EFSA) of the European
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:
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
(IARC) are based on the systematic
assembly and review of all publicly available and pertinent studies by
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
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
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
In terms of carcinogenicity, the EFSA
assessment focused on the pesticide
active substance (and not its
formulations) and considered all available information, including the
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,
acute risks for the consumers have not
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
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.