After years of research, environmental scientists believe they have identified a link between urban stormwater runoff and substantial annual die-offs of coho salmon after heavy autumn storms in the Pacific Northwest.
For decades it was a mystery why as many as 90% of the salmon would die when migrating through urban streams in an attempt to spawn in the Seattle, Washington, area. This was pushing them to the verge of extinction according to the Governor’s Salmon Recovery Office.
The answer now appears to be a highly-toxic undocumented substance derived from a common ingredient in rubber tires, thought to be ubiquitous in more than 1.5 billion existing vehicles. It flows into freshwater streams from roadways during precipitation. All water samples during testing contained a specific chemical signature associated with particles shed from vehicle tires in motion, the research showed.
Lead scientists, Jenifer McIntyre at Washington State University and University of Washington (Seattle) engineering professor Edward Kolodzie, made the discovery working alongside federal agencies, utilities and conservation groups.
“We had determined [the die-offs] couldn’t be explained by high temperatures, low dissolved oxygen, or any known contaminant such as high zinc levels,” McIntyre said in a December statement about the investigation. “Then we found that urban stormwater runoff could recreate the symptoms and the acute mortality.”
As many as 10 of the state’s 14 threatened or endangered salmon species are not meeting current recovery goals, and five species are in crisis.
The scientists spent long hours isolating and testing molecules from some 2,000 chemicals in the tire-wear particles to identify whether a certain contaminant or combination of contaminants was particularly harmful. They narrowed it down to one named 6PPD-quinone.
During testing, 6PPD-quinone killed salmon within five hours of exposure to concentrations as low as 0.8 micrograms per litre, the scientists found.
In a statement following the release of the study in the journal Science, the U.S. Tire Manufacturers Association announced that it uses 6PPD because it “helps tires resist degradation and cracking, which is vital for passenger safety.” The association added that it is “committed to collaborating with researchers at the University of Washington and other scientists to better understand this product, fill knowledge gaps and determine next steps.”
Tire manufacturers recommended adding 6PPD to the Priority Products Work Plan for further evaluation.