A highly toxic chemical used in the production of millions of tires every year is killing salmon in the Pacific Northwest, and it is being detected in streams across Northern California, a new study finds.
Scientists have known for decades that stormwater runoff from roads, highways and other urban areas has been linked to high rates of coho salmon deaths in Washington state, where as many as 90% of salmon in the Puget Sound area have died before they could spawn.
The new study published in the research journal Science on Thursday has identified a culprit chemical for the first time — a commonly used preservative called 6PPD used to give tires longer life.
“I think the broader impact is as we have already found this in San Francisco (Bay) creek water as well as the road runoff,” said the study’s lead author, Zhenyu Tian, a researcher at the University of Washington Tacoma. “We believe this thing is a prevalent contaminant. Wherever you have a busy highway, you have runoff from there and you probably will detect it. Our detection rate for this chemical in runoff is almost always 100%. For coho salmon, it’s definitely a threat.”
As part of the study, stormwater running into four Bay Area waterways and creeks tested positive for deadly concentrations of the toxin known as 6PPD-quinone. The creeks that tested for high toxicity included Rodeo Creek in Contra Costa County, Elmhurst Creek near Oakland and two locations near Coyote Creek near San Jose.
As tiny pieces of tire break off on roads and highways, the preservative 6PPD interacts with ground-level ozone to create 6PPD-quinone, which in turn washes into creeks and rivers when it rains, according to the study. The study led by the University of Washington and Washington State University found the toxin was highly deadly, killing some young coho salmon in just four hours when exposed to it.
Estimated to have once numbered in the hundreds of thousands, coho salmon numbers in California have been devastated since the mid-20th century by human development, damming, habitat loss and changing climate and ocean conditions. Coho have been federally listed as an endangered species and are at risk of extinction on the Central California coast, where only 1% of the historic population remains.
State agencies and environmental groups have been working for decades to restore coho salmon populations between Santa Cruz County and the California-Oregon border, including remaining coho strongholds on Lagunitas Creek, in San Mateo and further north in the Klamath and Eel rivers.
The discovery of the toxin could help to inform further recovery efforts throughout the state, researchers said.
“Here in the tributaries that discharge into San Francisco Bay, we no longer have coho,” said Rebecca Sutton, a study co-author and senior scientist with the San Francisco Bay Estuary Institute, which tested Bay Area stormwater as part of the research. “But up north we still have coho and we want those populations to thrive. So removing stressors like this particular chemical could