WASHINGTON— The World Health Organization’s International Agency for Research on Cancer found today that atrazine, the second most widely used pesticide in the United States, is “probably carcinogenic to humans.”

The cancer designation was determined by a working group of 22 expert cancer researchers from 12 different countries. The researchers identified evidence from human epidemiological studies, animal studies, and laboratory assessments of whether atrazine exhibits key characteristics of a carcinogen, like DNA damage and oxidative stress.

“It is outrageously irresponsible that we still allow use of this dangerous poison in the United States,” said Nathan Donley, environmental health science director at the Center for Biological Diversity. “This finding is just the latest indictment of the industry-controlled U.S. pesticide oversight process that is failing to protect people and wildlife from chemicals linked to numerous health harms.”

Atrazine has been banned in more than 60 countries around the world due to its impacts on human health and the environment. It is a known hormone-disrupting pesticide linked to birth defects, multiple cancers, and fertility problems like low sperm quality and irregular menstrual cycles.

Atrazine, which contaminates the drinking water of 40 million people in the United States, is the nation’s most widely detected pesticide water contaminant.

This announcement comes as a 2024 study that followed nearly 50,000 pesticide applicators in Iowa and North Carolina for over two decades found exposure to atrazine was correlated with early onset prostate and lung cancer.

The WHO IARC is considered the gold standard for cancer research. Its approach to assessing pesticides is much more scientifically robust than the process used by the U.S. EPA, which has proposed reapproving U.S. use of atrazine.

Pesticide companies often complain that the IARC assessments do not include the companies’ findings. But IARC reviewers only consider published research that can be reviewed by independent scientists for accuracy and bias.

The EPA’s pesticide approvals — including of atrazine — are based almost entirely on pesticide companies’ confidential assessments of their own products, assessments that independent researchers cannot review for accuracy or bias. This was highlighted in the Trump administration’s Make America Healthy Again (MAHA) report.

Following his reelection President Donald Trump expressed concerns that the United States continues spending “billions and billions of dollars on pesticides,” compared to the European Union and yet has far worse health outcomes. He pledged that his administration would “ensure that everybody will be protected from harmful chemicals, pollutants, [and] pesticides.” As part of that pledge, he nominated Robert F. Kennedy Jr. to be secretary of the Department of Health and Human Services with a mandate to “go wild on the food.”

Trump stated that Kennedy is “looking into [pesticides] very seriously because maybe it's not necessary to use all of that.” Kennedy has often pointed to atrazine as among the worst pesticides and called for it to be banned.

“Despite its rhetoric to the contrary, there is no better friend of atrazine than the Trump administration,” said Donley. “Hiding behind the rhetoric of MAHA, EPA reapproval of a poison that’s likely to keep Americans sick for generations is moving ahead full steam.”

In 2015 IARC found glyphosate, the world’s most used pesticide ingredient, to be a probable cause of cancer. Although glyphosate has been approved by the EPA, Bayer, which now owns glyphosate-maker Monsanto, has reportedly paid out more than $10 billion to settle nearly 100,000 lawsuits from glyphosate users now suffering from cancer.

Background and Current U.S. Regulatory Status

In 2020 the first Trump administration reapproved atrazine, in the process scrapping protections for young children and allowing for more water contamination than previously allowed.

Following that, public-interest groups sued the EPA over its reapproval decision. The case was put on hold while the agency reassessed its decision, following which the EPA found that atrazine was so pervasive that an eighth of the continental United States was contaminated with levels of atrazine that can lead to dangerous concentrations in waterways. The Biden EPA came up with a mitigation proposal to accompany the atrazine approval.

However, the Center’s analysis of data from the EPA, U.S. Department of Agriculture, and pesticide industry found that the Biden-era plan would still allow extremely harmful levels of atrazine pollution in 99% of the nation’s 11,249 atrazine-contaminated watersheds.

The Trump administration has not taken any action to strengthen, finalize, or scrap this plan, despite its many promises to act on the most dangerous pesticides, including banning atrazine, as part of its Make America Healthy Again promises. Tough rhetoric on the dangers of atrazine in the initial Make America Healthy Again Commission’s report was replaced with industry talking points in the follow-up report following outcry and heavy lobbying by corporate agriculture.

The only action the Trump administration has taken on atrazine is a recent draft finding that the widely used pesticide does not pose an extinction risk to a single protected animal or plant, despite widespread contamination of the nation’s rivers, lakes and streams. And yet the EPA’s initial assessment of atrazine, in 2020, found that it was likely to harm more than 1,000 imperiled species.

The new designation paves the way for the EPA’s registration review process to allow atrazine to continue to be widely used.

Atrazine has also been designated by the state of California as a reproductive toxin, known to be linked to birth defects, reduced male fertility and reproductive toxicities in women. Exposure to it is also strongly correlated with a birth defect in infants called gastroschisis, where children are born with their intestines protruding through their belly. The condition requires surgery immediately after birth and a stay of weeks to months in the neonatal intensive care unit.