A new analysis of federal water data estimates that atrazine contamination at levels considered harmful to aquatic wildlife extends across nearly 860,000 miles of rivers and streams in the lower 48 states, renewing scrutiny of a widely used herbicide known for its endocrine effects in animal studies.

By yourNEWS Media Newsroom.

WASHINGTON — Atrazine contamination at levels associated with harm to aquatic wildlife may extend across more than one-quarter of all river and stream miles in the continental United States, according to a new analysis of federal environmental data that is renewing debate over one of America’s most heavily used herbicides.

The findings were reported Monday by The Guardian, which examined a new Center for Biological Diversity analysis of Environmental Protection Agency water-monitoring and modeling records. The environmental organization estimates that nearly 860,000 river and stream miles in the lower 48 states contain atrazine at concentrations it considers dangerous to aquatic ecosystems.

“The problem is vast,” Nathan Donley, a report co-author and environmental health science director at the Center for Biological Diversity, told The Guardian.

“Everyone recognizes this is a big problem, but the EPA has utterly failed to do anything about it for the last three or four decades.”

The estimate does not mean federal scientists physically sampled every one of the approximately 860,000 miles identified by the report. The Center said it combined EPA water-monitoring information with federal modeling data to identify watersheds expected to contain atrazine at levels of concern. That distinction is important when interpreting the nationwide figure.

The Center’s report, titled “Pernicious Pesticide: Atrazine’s Growing Threats to Drinking Water, Rivers, People, and Wildlife,” estimates that affected waterways cross more than 250 million acres — roughly one-eighth of the land area of the lower 48 states.

More than 20% of U.S. surface-water treatment facilities, reservoirs and drinking-water intakes draw from waterways identified in the analysis, according to the organization. The affected areas also contain at least 675,000 private and commercial wells supplying homes, restaurants, hotels and other businesses.

Atrazine is a triazine herbicide primarily used to control broadleaf and grassy weeds in crops including corn, sorghum and sugarcane. EPA says the chemical is also registered for other agricultural uses and for turfgrass. About 70 million pounds are applied to U.S. cropland annually, according to the Center’s analysis.

The herbicide remains legal in the United States but has been removed from use in many other countries.

The European Commission decided in March 2004 not to approve atrazine as an active pesticide ingredient and required European Union member states to withdraw authorizations for atrazine-containing plant-protection products by Sept. 10 of that year.

The Center says more than 60 countries have prohibited the chemical.

Atrazine has also become widely known outside agricultural and environmental circles because of research into its effects on amphibian sexual development — work that later became the basis for radio host Alex Jones’ much-mocked “gay frogs” commentary.

The scientific findings themselves are considerably more specific than that phrase suggests.

University of California, Berkeley biologist Tyrone Hayes and colleagues reported in 2002 that African clawed frog larvae exposed to atrazine at concentrations of 0.1 parts per billion or higher developed reproductive abnormalities, including hermaphroditism and demasculinization. The researchers also recorded sharply reduced testosterone at higher experimental concentrations.

Hayes’ group reported similar effects in American leopard frogs in 2003, with atrazine exposure beginning at 0.1 ppb associated with gonadal dysgenesis and testicular oocytes in laboratory experiments.

A frequently cited 2010 experiment went further.

Hayes and his colleagues exposed genetically male African clawed frogs to atrazine and reported that the herbicide demasculinized exposed males and caused complete sex reversal in a portion of them. Ten percent of the exposed genetic males developed into functional females capable of mating with unexposed males and producing viable eggs, while other males showed reduced testosterone, fertility and reproductive behavior.

That research provides evidence of endocrine disruption and altered sexual development in amphibians. It does not demonstrate that atrazine changes sexual orientation in frogs or humans, and the popular “gay frogs” description is not a scientific characterization of the findings.

Research into atrazine’s amphibian effects has also not been completely uniform.

Other studies have reported no consistent effects on frog development or sexual differentiation under particular experimental conditions. A 2009 study of African clawed frogs, for example, found no aromatase induction or measurable effect on several markers of sexual differentiation after specified exposures, while other researchers have reported inconsistent relationships between environmental atrazine concentrations and reproductive abnormalities in wild frogs.

The EPA has previously reviewed conflicting amphibian studies while separately recognizing concerns about atrazine’s effects on aquatic plant communities, which form the base of freshwater ecosystems.

Hayes, however, told The Guardian that he believes the low-dose evidence is sufficiently concerning to argue against continued use.

“The effects are very clear, and in my opinion there is no safe level at which atrazine can be used because it is active in amphibians at .1 ppb, and there can be atrazine at 100 times that in rainfall,” Hayes said.

Hayes’ “no safe level” statement represents his scientific judgment and is not the regulatory standard currently used by EPA.

Federal standards use different concentration thresholds for different endpoints.

The EPA’s maximum contaminant level for atrazine in public drinking water is 3 micrograms per liter, equivalent to 3 parts per billion. That limit applies to drinking-water regulation and should not be confused with thresholds used for ecological protection.

For aquatic ecosystems, EPA announced in 2024 that it had recalculated the atrazine concentration-equivalent level of concern, or CE-LOC, to 9.7 micrograms per liter as a 60-day average.

EPA defines that figure as the concentration at which atrazine is expected to adversely affect aquatic plant communities. Protecting those plant communities is intended to also protect fish, amphibians and invertebrates that depend on them.

EPA’s previous scientifically derived ecological level of concern had been 3.4 micrograms per liter. Following additional review by a FIFRA Scientific Advisory Panel and reassessment of underlying studies, the agency raised that figure to 9.7 micrograms per liter in 2024.

Those regulatory numbers should not be directly compared as though they represent the same biological effect as Hayes’ 0.1-ppb frog experiments.

The 0.1-ppb finding concerns particular reproductive outcomes in particular amphibian experiments. The 3-ppb federal standard governs human drinking water, while the 9.7-ppb EPA ecological benchmark is based primarily on effects to aquatic plant communities over a 60-day average.

The new Center for Biological Diversity report identified five regions as national atrazine hot spots: the Chesapeake Bay watershed, the Midwest Corn Belt, Florida’s Lake Okeechobee, the lower Mississippi River and the Texas Gulf Coast.

The Midwest Corn Belt showed some of the broadest contamination in the analysis.

In Kansas, Nebraska, Iowa, Missouri, Illinois, Indiana and Ohio, the Center estimates that more than two-thirds of river and stream miles contain atrazine at concentrations it considers harmful. The affected area encompasses more than half of the region’s wells and approximately 68% of surface-water drinking facilities, according to the report.

The Guardian noted that states in this region have also experienced rising diagnoses of early-onset cancer compared with other portions of the country.

That geographical overlap does not establish that atrazine exposure caused those cancers. Cancer trends can be influenced by numerous demographic, environmental, lifestyle, occupational and diagnostic factors, and population-level associations cannot establish individual causation.

Concerns about cancer nonetheless intensified after the International Agency for Research on Cancer reevaluated atrazine in 2025.

A working group of 22 international scientists classified atrazine as “probably carcinogenic to humans,” or Group 2A. IARC cited limited evidence for cancer in humans, sufficient evidence from experimental animals and strong mechanistic evidence from experimental systems. Positive human associations were observed for a subtype of non-Hodgkin lymphoma involving the t(14;18) chromosomal translocation.

IARC’s classification identifies a cancer hazard; it does not quantify the cancer risk a particular person faces at typical environmental exposure levels.

The IARC conclusion also differs from EPA’s older cancer assessment. EPA previously classified atrazine as “not likely to be carcinogenic to humans,” based largely on its determination that the mechanism producing mammary tumors in a particular rat strain was not relevant to humans.

The difference illustrates how scientific agencies can reach different conclusions because they evaluate evidence under different frameworks and at different times. IARC’s Group 2A classification is substantially newer, having been announced in November 2025.

The Chesapeake Bay region is another major area highlighted in the Center’s analysis.

The organization estimates that more than 15,000 river miles across approximately 5.5 million acres of the watershed contain atrazine at levels it characterizes as harmful to aquatic ecosystems. About 18 million people live throughout the Chesapeake Bay watershed, which supports more than 3,600 plant and animal species.

The Center attributes much of the contamination to intensive corn production and associated herbicide use.

Farther south, the report identifies atrazine-contaminated watersheds along much of the lower Mississippi River.

Some of those watersheds are modeled or measured at more than five times EPA’s current ecological level of concern, according to the Center and The Guardian. Approximately 20 million people obtain drinking water from the Mississippi River system, while runoff from more than 40% of the continental United States eventually drains through the river toward the Gulf of Mexico.

Florida’s Lake Okeechobee was also designated a hot spot.

The roughly 730-square-mile lake is surrounded by approximately 500,000 acres of sugarcane fields, where atrazine is among the herbicides used for weed control. The lake is also heavily used for fishing, boating and other recreation.

On the Texas Gulf Coast, the Center identified more than 6 million acres covering over 6,000 river miles with atrazine levels it says threaten aquatic wildlife.

The organization also reported that Texas has more public water utilities reporting atrazine contamination than any other state and estimated that nearly 15 million residents receive drinking water from systems where atrazine has been detected. Detection does not necessarily mean the water exceeds EPA’s 3-ppb drinking-water limit.

That distinction is critical.

The presence of atrazine in a source-water watershed does not automatically mean treated tap water exceeds federal safety standards, nor does every detection represent the same level of exposure.

Public water systems covered by the Safe Drinking Water Act monitor for atrazine and must comply with the federal maximum contaminant level.

EPA records going back decades nevertheless demonstrate that atrazine is unusually widespread in American water. Historical federal monitoring found the herbicide far more frequently in surface water in agricultural areas than in undeveloped locations.

Federal regulators have repeatedly revisited atrazine because of those environmental concerns.

EPA’s current registration-review process has proposed nationwide runoff-reduction requirements, including restrictions on applications during rain or when soils are saturated and reductions in annual application rates for corn and sorghum.

The agency has also proposed additional mitigation requirements in watersheds predicted to exceed its 9.7-ppb ecological level of concern. Those measures can include conservation practices intended to reduce pesticide runoff from agricultural land.

The Center for Biological Diversity argues those measures do not go far enough and is advocating a complete ban.

Donley and the organization have also participated in litigation challenging EPA’s regulation of atrazine.

EPA and Syngenta, one of the major manufacturers and marketers of atrazine products, did not immediately respond to The Guardian’s requests for comment on the new analysis.

The Center maintains that the scale of contamination documented using EPA’s own records demonstrates that incremental mitigation has failed.

EPA, however, describes atrazine as an important agricultural herbicide and says its regulatory process is intended to balance agricultural benefits with measures needed to prevent unreasonable adverse effects on human health and the environment.

Atrazine’s history also helps explain why the chemical remains a contentious environmental issue.

Its widespread agricultural use makes it economically important to corn and other commodity producers, while its mobility in water allows it to travel away from treated fields through runoff, groundwater and, in some circumstances, atmospheric transport and precipitation.

Hayes’ amphibian research brought that debate into public consciousness long before the new national contamination analysis.

His studies documented reproductive changes in frogs at low experimental concentrations, and a later review led by Hayes argued that demasculinizing and feminizing effects were observed across multiple vertebrate classes.

Alex Jones later transformed that scientific literature into the far less precise claim that chemicals in water were “turning” frogs gay — a statement that became an internet meme.

The underlying research did not find that atrazine changed frogs’ sexual orientation. It examined biological sex development, reproductive anatomy, hormone levels and fertility.

That difference does not negate the documented endocrine effects reported in Hayes’ experiments, but it does separate the peer-reviewed findings from the viral political and cultural shorthand that developed around them.

The newest controversy is broader than frogs.

The Center’s analysis asserts that atrazine contamination at ecologically concerning levels now affects a substantial portion of America’s freshwater network, including watersheds feeding drinking-water facilities and hundreds of thousands of wells.

Because those estimates are derived partly from federal modeling rather than direct measurement of every mile of waterway, they should be understood as an assessment of the probable geographic extent of contamination rather than a nationwide census of individual water samples.

Even with that limitation, the scale is substantial: nearly 860,000 miles of rivers and streams, more than 250 million acres and five major regional hot spots, according to the report.

And with IARC now classifying atrazine as probably carcinogenic to humans, EPA continuing its registration review and environmental groups pressing for a national prohibition, the chemical’s future in American agriculture is likely to remain contested.

For Hayes, the amphibian evidence alone is enough to warrant stronger action.

“The effects are very clear, and in my opinion there is no safe level at which atrazine can be used because it is active in amphibians at .1 ppb, and there can be atrazine at 100 times that in rainfall,” he said.

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