Atrazine

In November 2025, the International Agency for Research on Cancer (IARC) announced it classified atrazine as a probable carcinogen (Group 2A). The classification reflects its mandate to determine if a substance could cause cancer from a potential hazard perspective.

IARC did not establish a causal link between atrazine exposure and an increase in cancer risk. 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 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 US, 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.

The following are relevant statements by various regulatory agencies and other scientific expert bodies:

• US Environmental Protection Agency (EPA, 2018): “the totality of the available evidence does not support an association between atrazine exposure and human cancer.”²
• Canada Pest Management Regulatory Agency (PMRA, 2023): “The evidence from the available epidemiological studies does not support a cause-and-effect relationship between atrazine use and any adverse health outcome.”³
• Joint FAO / WHO Meeting on Pesticide Residues (JMPR, 2007): “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.”⁴

IARC and regulatory authorities employ fundamentally different methodological approaches when evaluating the potential carcinogenicity of substances.

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 practices.

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.

Over the years, IARC has evaluated the carcinogenicity of various agents, including occupational and environmental exposures as well as chemical and biological agents.

IARC also classifies very hot beverages, red meat, working the night shift and hairdressing as Group 2A carcinogens.

No. In ensuring the safety of our drinking water, regulatory authorities implement strict limits that incorporate significant safety buffers. In the case of the US, for example, the regulatory authority EPA has set the limit for atrazine at 1/1000th of the level where adverse human health effects are no longer detected - at 3 parts per billion (ppb). This is equivalent to three drops in an Olympic-sized swimming pool.

At this level, an adult weighing 150 pounds / 70 kilograms could drink the equivalent of 12 bathtubs of water (483 gallons / 1800 liters) every day and still not ingest sufficient atrazine to experience adverse health effects. The recommended daily intake of water is approximately 0.5 gallons / 2 liters for an adult.

No. The EPA states: “no evidence was found that leads the Agency to conclude that there is a causal association between exposure to atrazine and neuroendocrine toxicity, including increased sensitivity to infants and children”⁵, following a comprehensive review of published epidemiology studies examining the potential for reproductive effects or birth defects in the human population.

While some studies claim endocrine-disrupting effects, it is important to understand some of their limitations. These include exposing rodents at doses substantially higher than maximum human exposure levels, or in-vitro laboratory studies which used solvents that artificially forced the chemical into cells in a way that cannot occur in living organisms and thus cannot possibly represent real-world metabolism or exposure in humans.

Regulatory authorities consider the strengths and weaknesses of all studies and base their conclusions on a weight-of-evidence approach.

In 2003, a research paper claimed atrazine had endocrine disruptor effects from a study performed by one researcher on frogs produced from a transgender strain that does not occur in nature, which no one has been able to reproduce, that the US EPA has dismissed, and that the overwhelming body of evidence contradicts. The sensationalized claim about “atrazine turning frogs gay" popularized by online conspiracy theorists has been debunked.

While some studies have explored the potential link between exposure to atrazine and gastroschisis – a birth defect where a baby’s abdominal wall does not close completely - no scientist or doctor has ever concluded in a peer-reviewed scientific analysis that atrazine causes this birth defect. In fact, authors of a recent study acknowledged: “…our results indicate an association between county-level atrazine use and incidence of gastroschisis but does not necessarily imply causation.” (Krishnapura, 2024).

No. Atrazine is currently registered for use in some 50 countries, including nations that lead the world in producing corn, sorghum, sugarcane and other major crops. In addition to the U.S., countries that approve the use of atrazine include Brazil, Argentina, China, Japan, Canada, Australia and many others.

Atrazine is no longer registered in the European Union. The EU sets a very conservative, arbitrary default threshold for all pesticides in groundwater at 0.1 ppb – this is 1,000 times lower than the level the World Health Organization (WHO) considers safe for atrazine in drinking water. For that reason, atrazine is no longer registered in the European market, even though the EU has never determined that atrazine is unsafe to humans or the environment.

Pesticides, particularly herbicides such as atrazine, have enabled the era of no-till farming, decreasing cropland under tillage by nearly 30%. Reversion to tillage not only releases greenhouse gases but also undermines significant efforts to mitigate soil erosion and eutrophication resulting from nutrient runoff (Brain et al., 2023). The United States Department of Agriculture (USDA) states: “The potential benefits of no-till are well-documented, from improving soil health to reducing annual fuel and labor investments”. In addition to significant fuel savings, the USDA indicates that fields recurrently managed under no-till practices generally have a higher water holding capacity, reduced soil erosion, increased soil biological activity and increased soil organic matter. The Environmental and Energy Study Institute (EESI) further suggests that “no-till farming mitigates climate change in two ways: it reduces the use of fossil fuel-powered machinery and it helps soil hold on to carbon, preventing the release of greenhouse gas emissions during tillage. Because no-till farming does not require a tractor to pull a plow, it saves fuel, cutting emissions”.