Tires and Coho Salmon Don't Mix

After years of studying why most adult coho salmon die when they reach Seattle's urban waters on their way to reproduce in streams connected to Puget Sound, a research team from the Universities of Washington and Washington State have isolated a cause among a witches brew of chemicals from roadway runoff poluting the Sound. The culprit is a globally common chemical used to preserve vehicle tires. When the tire antioxidant 6PPD interacts with atmospheric ozone it becomes toxic 6PPD quinone fatal to spawning salmon. Antioxidnats like 6PPD are added to tire compounds to inhibit oxidation of structural elastomeres. The research results are published in Science journal.

Urban runoff mortality syndrome, as the phenomenon of coho deaths is called, kills 40-90% of returning salmon before they are able to spawn. [photo: NOAA] Obviously this rate of mortality for a keystone species is not sustainable. The researchers used mass spectrometry and nuclear magnetic resonance to isolate the causative chemical in stormwater runoff. Detected concentrations of this chemical in receiving waters often exceeds the mortality thresholds for coho salmon during runoff events, which are quite common in the rainy Northwest. 

Globally, 3.1 billion tires are made annually that produce almost 1 kg of rubber particles per capita, making tires one of the most significant contributors of microplastics to the freshwater environment. Disposal of used tires also poses an environmental contamination risk. Research has shown that rainbow trout are more affected by used tires than new ones. It is unlikely, according to the researchers that coho are uniquely affected by the tire antioxidant. They recommend that non-toxic alternatives for 6PPD be utilized in tire manufacture, and more careful toxicological assessments be made of high volume commercial chemicals subject to pervasive discharges into the environment.