PORTLAND, Ore.— Pesticides and their highly toxic, long-lived breakdown products were found in 90% of the 442 U.S. streams sampled by federal scientists, according to a new study published this week by a journal of the American Chemical Society.

More than 1 billion pounds of pesticides are used each year in the United States. These poisons break down in the environment, forming compounds that are commonly detected in both surface and groundwater. Some of these pesticide breakdown products can be many times more toxic than the parent compound.

The breakdown products have also been found to trigger synergistic interactions that further increase their toxicity and harm water quality and wildlife, a problem documented by the five-year U.S. Geological Survey study.

“The pesticide industry has conditioned Americans to believe the fiction that these highly toxic pesticides just magically vanish,” said Jess Tyler, a scientist at the Center for Biological Diversity. “This study should be a wake-up call to the pesticide regulators at the Environmental Protection Agency, and the Biden administration, that they can’t keep ignoring the well-documented, systemic pesticide pollution of our landscapes and waterways.”

Water pollution by pesticides is dominated by some of the most widely use pesticides. Atrazine, the nation’s second most-used pesticide, was the most common pesticide found in 55% of surface water and nearly 70% of ground water. Even at low concentrations, it causes extreme harm to wildlife; at the levels allowed by the EPA in our drinking water it can chemically castrate frogs. The EPA recently determined that atrazine likely harms more than 1,000 endangered plant and animal species.

Pesticide breakdown products were found in small streams across the country, indicating that pesticides are probably causing chronic harm to species like endangered salmon and freshwater mussels that rely on small, unpolluted streams.

The study concludes that the impact from pesticide breakdown products may be higher than previously thought. Greater study of the toxicity of the breakdown products and regulation is needed to address these water pollutants to reverse the freshwater species extinction crisis.