The UN’s International Agency for Research on Cancer (IARC) said Friday (20 March) that three pesticides were “probably” carcinogenic and two others, which have already been outlawed or restricted, were “possibly” so.
IARC classified the herbicide glyphosate – the active ingredient in Roundup – and the insecticides malathion and diazinon as “probably carcinogenic” on the basis of “limited evidence” of cancer among humans.
The insecticides tetrachlorvinphos and parathion were classified as “possibly carcinogenic” in the light of “convincing evidence” from lab animals, the IARC said in a statement.
The classification, made by an expert panel, is not binding, said the IARC, an agency based in Lyon, that comes under the aegis of the World Health Organization (WHO).
“It remains the responsibility of individual governments and other international organisations to recommend regulations, legislation or public health intervention,” it said.
Glyphosate – introduced in the 1970s under the brand Roundup but now manufactured generically – is the most-produced weed killer in the world, the IARC said.
Agricultural use of it has surged since the introduction of crops genetically modified to be resistant to the chemical, enabling farmers to douse a field in one go, to kill weeds.
“The general population is exposed (to glyphosate) primarily through residence near sprayed areas, home use and diet, and the level that has been observed is generally low,” the IARC statement said.
The evaluation of glyphosate saw “limited evidence” of a type of cancer called non-Hodgkin lymphoma, as seen in studies in the United States, Sweden and Canada conducted among farm workers since 2001.
In 1985, the US Environmental Protection Agency (EPA) classified glyphosate as “possibly carcinogenic for humans” on the basis of experiments on lab mice.
In 1991, though, it took another look at those experiments and changed the classification to “evidence of non-carcinogenicity” in humans.
Monsanto rejects classification
The US agribusiness giant Monsanto, which manufactures Roundup, strongly contested the IARC classification.
“Each of the studies considered by IARC have been previously reviewed and considered by regulatory agencies – most recently by the German government on behalf of the European Union,” it said in a press release.
“Relevant, scientific data was excluded from review,” it charged.
“(The) IARC received and purposefully disregarded dozens of scientific studies – specifically genetic toxicity studies – that support the conclusion glyphosate is not a human health risk.”
Malathion is used in substantial volumes throughout the world, with agricultural workers being the most exposed to it, the IARC said.
Diazinon production has been low and decreased further after 2006, following restrictions being placed on it in the United States and the European Union.
Tetrachlorvinphos is banned in the EU, but in the United States, it continues to be used on livestock and pets, including in flea collars.
“Parathion use has been severely restricted since the 1980s. All authorised uses were cancelled in the European Union and the USA by 2003,” IARC said.
The IARC has four categories: “carcinogenic” (group 1), “probably carcinogenic” (group 2A), “possibly carcinogenic” (group 2B), “not classifiable” (group 3) and “probably not carcinogenic to humans” (group 4).
The term “limited evidence” means its experts, in a review of research, found an association between exposure to the chemical and cancer.
However, chance or confounding factors cannot be ruled out, according to this definition.
A summary of the assessment was published online in the journal The Lancet Oncology.
Independent experts contacted by Britain’s Science Media Centre (SMC) said they did not see a clear case of cancer risk for glyphosate, and some queried the IARC’s methodology.
“There are over 60 genotoxicity studies on glyphosate with none showing results that should cause alarm relating to any likely human exposure,” said Colin Berry, emeritus professor of pathology at Queen Mary University of London.
“The IARC report does not raise immediate alarms,” said David Coggon, a professor of environmental medicine at Britain’s University of Southampton.
“However, I would expect regulatory authorities around the world to take note of this new evaluation, and to consider whether it indicates a need to review their risk assessments for any of the pesticides that they currently approve.”
Amid growing public concern over the impact of pesticides, the European Commission in 2006 presented a 'pesticides package' aimed at protecting human health and the environment from their dangerous or excessive use in agriculture.
Agreement on the package was reached in December 2008. The new regulations divide the EU into three zones (north, centre, south) inside of which mutual recognition of pesticides will become the rule.
However, member states will still be allowed to ban a product on the basis of specific environmental or agricultural circumstances:
- Certain highly toxic chemicals, namely those which are genotoxic, carcinogenic or toxic to reproduction (unless their effect would in practice be negligible) including neurotoxic, immunotoxic and certain endocrine-disrupting substances, if deemed to pose a significant risk
- Asks member states to adopt national action plans on safer use of pesticides as well as overall usage reduction targets
- Bans aerial crop spraying, with exceptions subject to approval by member-state authorities
- Asks member states to establish approporiate measures, such as buffer zones, to protect aquatic organisms, and
- Bans the use of pesticides in public places, such as parks and school grounds, or at the very minimum asks for their use to be restricted.
The European Parliament voted to seal the agreement in January 2009.
International Agency for Research on Cancer (IARC)
- Press release: IARC Monographs Volume 112: evaluation of five organophosphate insecticides and herbicides (20 March 2015)
- Full article in The Lancet Oncology
- Press release: Monsanto Disagrees with IARC Classification for Glyphosate (20 March 2015)