Nathaniel L. Scholz, J. W. Davis, Julann A. Spromberg, Blake E. Feist, Tiffany L. Linbo, Jana S. Labenia, James Cameron, Barbara L. French, David H. Baldwin, John P. Incardona, Tracy K. Collier
High Resolution Image Download MS PowerPoint Slide In 2020, an environmental transformation product of the synthetic tire additive N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), or 6PPD-quinone, was identified as the causative chemical agent for a mysterious and recurring mass mortality syndrome affecting adult coho salmon ( Oncorhynchus kisutch ) as they returned from the ocean to spawn in restored urban streams. A few years hence, 6PPD-q and related tire chemicals have become a global research focus in aquatic ecotoxicology, environmental engineering, and public health. Here we review the two-decade forensic investigation that led to the discovery of 6PPD-q, including converging lines of evidence from field surveys, landscape modeling, stormwater bioassays, and green infrastructure effectiveness studies. As the body of knowledge around 6PPD-q rapidly grows, we consider implications for Pacific salmon conservation, stormwater management, river restoration, and urban ecology. Finally, we highlight research priorities identified by the authors to inform salmon recovery efforts in urbanizing watersheds that are increasingly impacted by polluted nonpoint source runoff.