SEATTLE — Toxic runoff that flows from highways into urban streams is killing coho salmon in Puget Sound, but simple filtering methods can help fish survive, a new study finds.
Salmon exposed to untreated highway runoff in controlled experiments became lethargic, lost their orientation and died within hours, according to the study published Thursday in the Journal of Applied Ecology.
But fish survived if they were immersed in runoff that had been filtered through columns of sand and soil, similar to rain gardens.
The study found inexpensive pollution-prevention tools that completely prevented the toxic impacts to the fish, said Julann Spromberg, the paper’s lead author and toxicologist affiliated with the National Oceanic and Atmospheric Administration in Seattle.
All fish exposed to untreated highway runoff died within 24 hours, while fish exposed to the treated water survived.
Spromberg said she was most surprised to find that the fish weren’t affected by an artificial mixture of heavy metals and oils that the researchers produced in the lab. But actual runoff collected from a Seattle highway caused the fish to die.
Heavy metals and oil products weren’t enough to kill fish, she said. “There’s something out there that we’re not measuring that’s causing it,” but scientists haven’t pinpointed what chemical or compound of chemicals in the runoff is lethal to salmon, she added.
Knowing that may help control toxic chemicals at its source, she said.
Rick Cardwell, an aquatic toxicologist not involved in the study, praised its findings. “This is really a good study that really would have a lot of impact,” he said, though he would like to see the experiments independently repeated.
In the meantime, the study suggests that rain gardens, bioretention swales and other so-called green stormwater infrastructure that manage stormwater with natural drainage should be incorporated where possible.
Nat Scholz, who manages NOAA’s Ecotoxicology Program in Seattle, said wild salmon may have a shot if such strategies are used.
