In Oregon, Clackamas County Streams Have High Pesticide Levels

A turbid Lost Dog Creek tumbles down steep slopes before feeding Lake Oswego. (Credit: Public Domain)

As part of an effort to comply with an Oregon Department of Environmental Quality permit, researchers with the U.S. Geological Survey (USGS) have wrapped up a study of pesticides flowing through Clackamas County streams. Their results, gathered during storm events in 2013, point to levels of pesticides above benchmarks set by the U.S. Environmental Protection Agency (EPA) to protect aquatic life.

They focused on western Clackamas County, which is home to the highly urbanized greater Portland area, and sampled for 91 pesticides dissolved in water and 118 of them on the sediments. Nearly all of the streams sampled, scientists say, contained at least one insecticide at levels that surpassed those set for aquatic life.

The active ingredients of the insecticides detected included the chemicals bifenthrin, fipronil, malathion, breakdown products of DDT (dichlorodiphenyltrichloroethane) and others. But the chemical that seemed to cause the most harm was bifenthrin, a broad-spectrum insecticide used to kill insect pests around homes and businesses.

Bifenthrin attaches tightly to sediments contained in stormwater, traveling from areas where it’s applied through storm drainage systems to streams. When even small amounts of the chemical are mobilized, beneficial insects can be impacted when sediments and the chemical settle out in streams.

To measure levels of that insecticide and others, USGS scientists used sediment traps and stainless steel spoons to collect stream sediments for analysis. Amber-glass bottles were used to gather stormwater runoff from outfalls for processing. In addition, invertebrate surveys were also completed and compared alongside pesticide data to glean some of their effects.

Tanner Creek outfall delivers stormwater runoff with insecticides to Tanner Creek, tributary of the Willamette River. (Credit: Public Domain)

Bifenthrin was detected in all five stormwater outfalls sampled, and 73 percent of streams sampled during a September storm, sometimes at levels well above EPA benchmarks. Seventy-one percent of streams contained bifenthrin in streambed sediments at levels likely to affect aquatic insects.

Streams with no or low levels of bifenthrin in their sediments had significantly more aquatic insects such as mayflies, caddisflies and stoneflies than streams with high concentrations of bifenthrin. Streams with high sediment levels contained mostly pollution-tolerant organisms, primarily non-insects.

“Numerous pesticides were detected in stormwater runoff and streambed sediments, with two insecticides — fipronil and malathion — occurring at concentrations exceeding EPA acute benchmarks for aquatic invertebrates,” scientists write in the study, full results of which are published in the Journal of Environmental Monitoring and Assessment. “Concentrations of bifenthrin exceeded the EPA 21-day chronic benchmark for invertebrates, though reported concentrations were instantaneous values that may overestimate potential toxicity if these elevated concentrations were short lived.”

Scientists commend the 13 local governments involved in the work that came together to design and fund the study with the USGS. Each of them could have implemented separate, and much smaller, monitoring efforts without assistance from the Geological Survey, but working together helped to create higher-quality study results for everyone involved at much lower cost.

Top image: A turbid Lost Dog Creek tumbles down steep slopes before feeding Lake Oswego. (Credit: Public Domain)