Chemical derived from car tires transforms toxic streams, kills salmon

For Pacific Northwest salmon, returning to spawn in streams and creeks near urban areas can be a death sentence, thanks to a ubiquitous additive in vehicle tires, a new study reveals. The results show that 6PPD-quinone – a highly toxic oxidation product of tire rubber particles – transforms toxic streams and may be responsible for the annual deaths observed among migrating adult salmon in the US Pacific Northwest. For decades, researchers have observed regular acute mortality events affecting adult coho salmon (Oncorhycchus kisutch) migrating into urban waterways contaminated by rainwater runoff. In more urbanized catchment areas, urban runoff mortality syndrome (URMS) is estimated to kill 40-90% of returning salmon before they have a chance to spawn. Although URMS has been linked to stormwater runoff and potentially linked to tire tread wear particles (TWPs) – one of the most significant sources of microplastics in freshwater – the one or more toxic agents responsible for the killing of the salmon remained elusive. Using liquid chromatography mass spectrometry and nuclear magnetic resonance, Zhenyu Tian and colleagues explored compounds associated with road runoff and TWP to look for toxic compounds. Tian et al. found that 6PPD, the major antioxidant chemical used in tire rubber, reacts with ozone to form the previously unidentified 6PPD-quinone compound. According to the authors, 6PPD-quinone is highly toxic and deadly to juvenile salmon at concentrations of around 1 microgram per liter. Furthermore, retrospective analysis suggests that this deadly compound is widespread in rainwater-affected streams across the west coast of the United States. “Coho salmon are unlikely to be particularly sensitive and the toxicology of transformation products of 6PPD in other aquatic species should be evaluated,” the authors write.

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