In the Midwest, where intensive agriculture is practiced, a federal study has found some of the most alarming levels of pesticides in U.S. rivers, with pollution levels regularly reaching levels that could harm aquatic life.
What's happening?
At most sites, a decade-long U.S. Geological Survey study found at least one chemical in concentrations that could harm aquatic plants or stream invertebrates, such as stoneflies and mayflies, KCUR reports.
To create the database, scientists took samples from 81 stream sites between 2013 and 2022 and analyzed them for 80 chemicals.
Approximately two-thirds of the sites exceeded both acute and chronic thresholds, and 19 pesticides exceeded EPA benchmarks. Acute exposure refers to more immediate damage, while chronic exposure refers to lower concentrations that persist over time.
The network repeatedly reported the presence of atrazine, metolachlor, and imidacloprid. Of these, atrazine was detected in acute concentrations in most locations, while imidacloprid appeared most frequently in chronic concentrations.
Meg Shoda, a hydrologist with the U.S. Geological Survey in Cleveland and the study's lead author, told KCUR that the patterns they found are consistent with what scientists already know about runoff from intensive agriculture: "There's a lot of agricultural activity in this basin.".
Why is this important?
Damage to the smallest elements of a river's ecosystem can spread over large areas. Since human well-being is linked to the health of water bodies, pesticides that harm aquatic plants and insects can spread up the food chain, deplete oxygen levels in the water, alter habitats, and weaken fish and bird populations.
Sydney Evans, a senior science analyst at the Environmental Working Group, said, as reported by KCUR, "Atrazine has been around for a very, very long time. It's a hormone disruptor, so we're concerned about its use.".
Atrazine has been detected in water samples from more than 2,000 water utilities serving 40 million people, according to the Environmental Working Group's tap water database.
While research on human health effects is still underway, some studies have linked exposure to birth defects or developmental problems, and the herbicide has already become one of the most common pollutants in U.S. surface waters.
What is being done?
Shoda described the USGS's work as "the largest continuously monitored network in the country," but noted that routine checks may not detect pollution spikes caused by rain.
For this reason, she warned, according to KCUR, "data received at this rate is likely an underestimate of actual conditions.".
Public health advocates are also calling for broader oversight. The Environmental Working Group is pushing for expanded testing of drinking water for imidacloprid, which the Environmental Protection Agency (EPA) has not yet included on its limited list of unregulated chemicals monitored in public water supplies.
Researchers also want to better understand how different pesticides interact in real water bodies, since river creatures are rarely exposed to just one chemical at a time.
Debbie Baker, a researcher at the Kansas Biological Center and the Center for Environmental Research, put it this way: "It's really important to see the local community.".
Shoda said one question about the polluted streams still remains unanswered: "What is the toxicity of this substance?"«
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