Syngenta’s statement on atrazine and IARC’s reclassification
- IARC does not establish a causal link between atrazine use and cancer in humans
- Current scientific evidence clearly demonstrate that atrazine is safe when applied in accordance with registered label instructions
- IARC also includes very hot beverages, red meat, working the night shift and hairdressing
in the same classification
Basel, November 21, 2025
At Syngenta, the health and well-being of people always come first. Atrazine is one of the most extensively studied substances worldwide, with more than 7,000 studies conducted over six decades and a long history of safe use. The weight of scientific evidence shows atrazine is safe when used according to the registered label instructions. We stand with the many regulatory authorities around the world who have concluded that atrazine can be used safely, and by the safety of all our atrazine products.
Understanding IARC’s classification
The International Agency for Research on Cancer (IARC)’s classification of atrazine as a probable carcinogen (Group 2A) reflects its mandate to determine if a substance could cause cancer from a potential hazard perspective. In fact, IARC – which is not a regulatory agency – does not determine the likelihood of cancer occurring at realistic levels of exposure (technically called “risk”). IARC’s reclassification did not establish a causal link between atrazine exposure and an increase in cancer risk.
The scientific consensus
IARC’s decision is wholly inconsistent with the scientific consensus held by close to 50 regulatory authorities and scientific expert bodies worldwide – including leading regulatory authorities in the U.S., Canada and Australia. These authorities have concluded that atrazine does not pose any carcinogenic risk and is safe when used in accordance with the registered label instructions.
- US Environmental Protection Agency (EPA): After reviewing hundreds of studies and multiple independent Scientific Advisory Panels – public meetings where a panel of independent experts reviews EPA decisions – the EPA concluded: “the totality of the available evidence does not support an association between atrazine exposure and human cancer.” (Atrazine. Draft Human Health Risk Assessment for Registration Review, 2018, page 62).
- Canada Pest Management Regulatory Agency (PMRA): "The evidence from the available epidemiological studies does not support a cause-and-effect relationship between atrazine use and any adverse health outcome.” (2023 Proposed Special Review Decision, page 32)
- Joint FAO/WHO Meeting on Pesticide Residues (JMPR): "The weight of evidence from the epidemiological studies did not support a causal association between exposure to atrazine and the occurrence of cancer in humans." (JMPR review, page 47)
The different methodological approaches and why it matters
IARC employs a fundamentally different methodological approach when evaluating the potential carcinogenicity of substances compared to US EPA and other regulatory authorities.
IARC reviews published scientific studies to determine if there is sufficient evidence that a substance might cause cancer in humans at any concentration. It does not systematically assess the quality nor consistency of these studies according to established scientific best practice.
Regulatory authorities conduct a more comprehensive evaluation, which also considers if a substance poses a risk of cancer under real-world conditions. They:
- Evaluate multiple data sources – including all available proprietary studies conducted to internationally-recognized standards;
- Integrate different types of data – including epidemiological data, animal data and mechanistic studies – while considering the quality and reliability of each dataset;
- Analyze disease processes and exposure effects in detail, identifying specific toxic effects and the mechanisms that lead to these effects.
Such methodological differences, combined with the regulatory authorities' consideration of risk management measures and exposure patterns, can lead to divergent conclusions about the same substance's carcinogenic potential.
National regulatory authorities are responsible in the implementation of relevant policies; IARC does not make policy recommendations.
Context on IARC classifications
Over the years, IARC has evaluated the carcinogenicity of various agents, including occupational and environmental exposures as well as chemical and biological agents. Recent classifications include:
- Group 1: Alcoholic beverages, processed meats, automotive gasoline and UV-emitting
tanning devices - Group 2A: Very hot beverages, red meat, night shift work, occupations such as hairdressing
- Group 2B: Aloe vera whole leaf extracts, pickled vegetables.
To note, IARC’s classification system often places substances with widely differing potencies and very different modes of action – such as smoked ham and the war agent mustard gas – in the same group, which has at times led to confusion in directing public health policies aimed at preventing cancer.
At Syngenta, we base the safety of our products on the highest standards of scientific rigor that adhere to strict, internationally recognized standards. We continuously evaluate the relevant science and have not found any credible data that demonstrates a causal link between atrazine use and cancer. We stand with the many regulatory authorities around the world who have concluded that atrazine can be used safely, and by the safety of all our atrazine products.
For more information about atrazine and relevant studies, please visit: www.atrazine.com.
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