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Who is the International Agency for Research on Cancer (IARC) and why have they classified glyphosate as a “probable human carcinogen”?

Category: Health

The IARC is the specialized cancer agency of the World Health Organization. Glyphosate was evaluated by IARC in March 2015, and labelled as a “2a - probable human carcinogen”. The IARC study looked at the overall hazard posed by glyphosate, concluding that glyphosate is, under some circumstances, capable of causing cancer. This hazard assessment carried out by IARC did not consider how the chemical is used in real life, unlike the risk assessment conducted by regulatory agencies such as the Pest Management Regulatory Agency (PMRA), the U.S. EPA and the European Food Safety Authority which consider both the hazard as well as the risk to humans under actual and typical conditions of use.

The International Agency for Research on Cancer (IARC) is the specialized cancer agency of the World Health Organization (WHO). The objective of the IARC is to promote international collaboration in cancer research. The Agency is inter-disciplinary, bringing together skills in various disciplines, including epidemiology, laboratory sciences and biostatistics to identify the causes of cancer so that preventive measures may be adopted and the burden of cancer may be reduced. A key component of IARC is the monograph program, which identifies environmental factors that can increase the risk of human cancer. These include individual chemicals, mixtures of several chemicals (eg, tobacco smoke), occupational exposures, physical agents, biological agents, and lifestyle factors. National health agencies in countries all over the world then use this information as scientific support for their actions to prevent exposure to potential cancer causing agents, known as carcinogens. IARC noted that glyphosate currently has the highest global production volume of all herbicides, potentially creating the opportunity for human exposure. Responding to advice from its international Advisory Group, glyphosate was evaluated at IARC’s monograph meeting in March 2015 (Lancet, 2015). On the basis of its evaluation of scientific evidence from studies in humans and in laboratory animals, IARC concluded that glyphosate should be classified as a “2a- probable human carcinogen”. It is important to be aware that IARC assessments are hazard based, meaning that the IARC evaluation considers whether a substance is capable of causing cancer, without necessarily considering if, under actual conditions of use, the substance will pose a real cancer risk. This contrasts sharply with risk based assessments carried out by regulatory agencies around the world, including the PMRA, US EPA and the European Food Safety Authority, which carefully consider the uses of a substance and potential for human exposure in determining if the typical use of a substance poses an increased cancer risk. In Canada, only those pesticide products, which present “reasonable certainty of no harm”, are registered by the PMRA. The PMRA has determined that the use of glyphosate in Canada meets its standard of “reasonable certainty of no harm”.

Recent developments

On May 16, 2016, a special meeting of the joint Food and Agriculture Organization and World Health Organization of the United Nations was held to re-evaluate glyphosate and other compounds in light of new studies that had become available since their last full assessment. The meeting concluded that glyphosate is unlikely to pose a carcinogenic or genotoxic risk to humans from exposure through the diet.

The distinction between hazard and risk is important in understanding the difference between what appears to be contradictory conclusions from IARC and the WHO. IARC considers the potential for a substance to cause harm under some circumstances, while regulatory agencies such as the PMRA, US EPA and the European Food Safety Authority, consider the likelihood (risk) of observing negative effects under realistic exposure levels. Regulatory agencies around the world, including PMRA, the United States Environmental Protection Agency (USEPA), the World Health Organization (WHO), and the European Food Safety Authority (EFSA) have, for many years, consistently concluded that registered uses of glyphosate in accordance with label directions do not pose a cancer risk, or any other risk, to human health.

In April 2015, the PMRA released their latest review of glyphosate and declared that the weight of evidence indicates that glyphosate does not present unacceptable risk to human health. The full PMRA glyphosate review can be found here or please visit here for a summary version of the full PMRA review.

WHO. Joint FAO/WHO Meeting on Pesticide Residues. Summary Report. May 16, 2016


Lancet. http://dx.doi.org/10.1016/S1470-2045(15)70134-8. March 20. 2015. Accessed on July 24, 2015.