Atrazine Herbicide Contaminates 25% of US Rivers: Hormone Threat to Drinking Water

The hormone-disrupting herbicide atrazine has contaminated nearly a quarter of all rivers in the contiguous United States—equivalent to 860,000 miles—at levels dangerous to wildlife and potentially threatening to human health. The findings come from a comprehensive review of Environmental Protection Agency (EPA) records released by the Center for Biological Diversity.

What makes the findings even more alarming is that the contaminated waterways cross more than 20% of the nation's surface drinking water intakes and affect more than 675,000 private and commercial wells. In other words, atrazine exposure is no longer confined to aquatic ecosystems; it has reached the water sources consumed by millions of people every day.

Atrazine is a herbicide that works by disrupting hormonal balance. In humans, exposure to the substance—even at very low levels—has been linked to impaired fetal growth, premature birth, birth defects, and low birth weight. The effects on the reproductive system are also serious: feminization of male gonads, irregular menstrual cycles, reduced sperm count and quality, and decreased fertility in both men and women. The International Agency for Research on Cancer (IARC) classifies it as a probable carcinogen.

The effects on wildlife are no less worrying. Research on frogs shows that atrazine exposure at levels as low as 0.1 parts per billion (ppb) can damage the development of reproductive organs and lead to population declines. Yet the official threshold for atrazine in human drinking water in the US is set 30 times higher, at 3 ppb. Tyrone Hayes, a pesticide researcher at the University of California, Berkeley, who first revealed atrazine's effects on the reproductive system of frogs, stressed that there is no safe level for the substance. "The effects are very clear, and I believe there is no safe level because atrazine is active in amphibians at 0.1 ppb, while in rainwater it can be 100 times that," he said.

The report analyzes the entirety of EPA's atrazine records for the first time and maps the extent of the threat. Nathan Donley, one of the report's authors and director of environmental health science at the Center for Biological Diversity, called the problem a neglected crisis. "Everyone knows this is a big problem, but the EPA has done absolutely nothing for the past three or four decades," he said. He blamed weak enforcement on the fact that atrazine is a highly profitable flagship Syngenta product, with estimated US sales of US$2–3 billion in 2025.

"We need to follow the lead of more than 60 countries around the world and ban atrazine forever. If we don't, the consequences will be disease, death, and dirty water in America for decades to come." — Nathan Donley, Center for Biological Diversity

The contamination map shows five main hotspots: the Chesapeake Bay area, the Midwest corn belt, Lake Okeechobee in Florida, the lower Mississippi River, and the Texas Gulf Coast. In the Midwest corn belt, which includes Kansas, Nebraska, Iowa, Missouri, Illinois, Indiana, and Ohio, more than two-thirds of river miles are contaminated, covering about half of the wells and 68% of drinking water treatment facility intakes. The region also records a spike in early cancer diagnoses compared with the national average. Meanwhile, in the lower Mississippi River, atrazine concentrations at many points exceed five times the threshold considered harmful to aquatic ecosystems.

Although atrazine has been banned in many developed countries, US regulators still face lawsuits from public health groups over the substance's approval. In 2020, the EPA promised to draft a plan to address water contamination, but the 2024 draft reviewed by Donley was deemed inadequate. "That plan isn't worth the paper it's printed on," he said. Litigation is expected to continue once the final plan is published. The EPA and Syngenta have not responded to requests for comment.

Indonesian Context

For Indonesia, the atrazine case in the US serves as an important mirror for pesticide management and protection of water sources. Atrazine is indeed not permitted to circulate in Indonesia—the Ministry of Agriculture banned it long ago—but similar challenges arise from other active ingredients still widely used in the plantation and food sectors. Weak monitoring of pesticide residues in rivers and groundwater can pose long-term health risks, especially for rural communities that depend on wells and surface water. Regulators and local governments need to strengthen water quality monitoring and evaluate pesticide permits periodically, rather than waiting for international reports.

Going forward, the question is not merely whether the EPA will ban atrazine, but how much health and environmental cost the public must bear before regulators act. If other countries have proven that a ban can be implemented, why are the US—and other developing countries—still hesitant?