Source: Komo News
Scientists at Washington State University’s Puyallup Research & Extension Center have uncovered how a common tire chemical kills coho salmon in Puget Sound streams. Coho salmon, which migrate between freshwater and ocean habitats, have long suffered mysterious die-offs after rainstorms. In 2018, researchers traced the deaths to particles from car tires, and by 2020 identified 6PPD, a preservative in nearly all tires, as the culprit.
The new study, led by Ph.D. student Stephanie I. Blair and published in Environmental Science & Technology, reveals the biological mechanism: when 6PPD reacts with ozone, it transforms into 6PPD-quinone, a toxic compound. This chemical breaches the blood-brain and blood-gill barriers—normally protective cellular walls—causing the salmon to suffocate. Laboratory experiments confirmed the damage by exposing fish to real stormwater runoff and 6PPD-quinone. The findings provide a clear explanation for “coho urban runoff mortality syndrome” and establish a framework for developing and testing safer alternatives to 6PPD, with implications for other species and human health.