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risk assessment


A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon Zhenyu Tian1,2, Haoqi Zhao3, Katherine T. Peter1,2, Melissa Gonzalez1,2, Jill Wetzel4, Christopher Wu1,2, Ximin Hu3, Jasmine Prat4, Emma Mudrock4, Rachel Hettinger1,2, Allan E. Cortina1,2, Rajshree Ghosh Biswas5, Flávio Vinicius Crizóstomo Kock5, Ronald Soong5, Amy Jenne5, Bowen Du6, Fan Hou3, Huan He3, Rachel Lundeen1,2, Alicia Gilbreath7, Rebecca Sutton7, Nathaniel L. Scholz8, Jay W. Davis9, Michael C. Dodd3, Andre Simpson5, Jenifer K. McIntyre4, Edward P. Kolodziej1,2,3*

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In U.S. Pacific Northwest coho salmon (Oncorhynchus kisutch), stormwater exposure annually causes unexplained acute mortality when adult salmon migrate to urban creeks to reproduce. By investigating this phenomenon, we identified a highly toxic quinone transformation product of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), a globally ubiquitous tire rubber antioxidant. Retrospective analysis of representative roadway runoff and stormwater-affected creeks of the U.S. West Coast indicated widespread occurrence of 6PPD-quinone (<0.3 to 19 micrograms per liter) at toxic concentrations (median lethal concentration of 0.8 ± 0.16 micrograms per liter). These results reveal unanticipated risks of 6PPD antioxidants to an aquatic species and imply toxicological relevance for dissipated tire rubber residues. H umans discharge tens of thousands of chemicals and related transformation products to water (1), most of which re- main unidentified and lack rigorous toxicity information (2). Efforts to iden- tify and mitigate high-risk chemical toxicants are typically reactionary, occur long after their use becomes habitual (3), and are frequently stymied by mixture complexity. Societal man- agement of inadvertent, yet widespread, chem- ical pollution is therefore costly, challenging, and often ineffective. The pervasive biological degradation of con- taminated waters near urban areas (“urban stream syndrome”) (4) is exemplified by an acute mortality phenomenon that has affected Pacific Northwest coho salmon (Oncorhynchus kisutch) for decades (5–9). “Urban runoff mor- tality syndrome” (URMS) occurs annually among adult coho salmon returning to spawn in freshwaters where concurrent stormwater exposure causes rapid mortality. In the most urbanized watersheds with extensive imper- vious surfaces, 40 to 90% of returning salmon may die before spawning

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