When autumn rains return to western Washington, so do coho salmon. But in many of the creeks they swim up, something in the water leaves fishes gasping for air. They die quickly, before they manage to spawn.

A new study points at chemicals from tiny bits of car tires as a prime suspect in the fishes’ untimely deaths. Most cohos that come to Miller Creek, in the leafy Seattle suburb of Normandy Park, die prematurely. On a sunny September morning, researcher Ed Kolodziej from the University of Washington spotted a dozen young cohos, each about two inches long, darting in and out of the shadows on Miller Creek. Their two-foot-long elders were likely just offshore, waiting for rains to raise the creek and creeks like it all around Puget Sound. Virtually every coastal stream in Washington where water flows year-round is home to coho salmon. But those rains also help send a toxic stew into urban and suburban creeks around the sound. “Stormwater flows actually kill these coho salmon before they have a chance to reproduce,” Kolodziej said. Heavy rains carry a chemical cocktail of motor oil, wiper fluid, brake dust and other gunk from roads and driveways into nearby drains, creeks and eventually Puget Sound. Stormwater runoff from highways and roads is the largest source of toxic chemicals in the sound, according to the Puget Sound Partnership.

Credit: KUOW Photo / John Ryan



Scientists have long known that road runoff kills cohos, but they still do not know which of the thousands of chemicals in it are the lethal ones for suburban salmon. To narrow down the lineup of suspects, salmon researchers enlisted volunteer creek watchers. In creeks in Seattle and Normandy Park, they went on the lookout for coho acting weird, swimming aimlessly and gasping for breath: signs they were about to die an unnatural death. Lab tests showed the runoff that was killing cohos consistently had some unexpected ingredients. “We were surprised to see a really strong signal of chemicals coming out of car tires, actually,” Kolodziej said. Their findings appear in the journal Environmental Science and Technology. Researchers found chemicals used in tire manufacturing, including diphenylguanidine and the nearly unpronounceable hexa(methoxymethyl)melamine, or HMMM. “It's a real mouthful, but quite common actually in some of our urban creeks,” Kolodziej said. Even so, the new study says it is the first to report finding HMMM in a North American waterway.

Miller Creek in Normandy Park, Washington. KUOW / John Ryan. Sheens of motor oil or antifreeze can be seen on many roadways and parking spaces. But driving also leaves little smears of tire behind. “As our tires wear out, we're leaving bits of that tire rubber behind on our roadways,” Kolodziej said, “and chemicals are actually leaching out of that tire rubber and polluting our stormwater and subsequently polluting our urban creeks.” Paper coauthor Jenifer McIntyre, an ecotoxicologist at Washington State University in Puyallup, is now testing different components of worn tires to try to zero in on what is killing these suburban salmon. "These chemicals are out there. They're there in our creeks," Kolodziej said. "We should understand them better."

Credit: Peter et al., Environmental Science & Technology, 2018.