School of Engineering, The University of Tokyo　Research Center for Water Environment Technology

For several decades researchers in the Seattle, WA in the United States have witnessed mass pre-spawn mortality events of coho salmon in highly urbanized streams, a significant threat to these populations. In 2021, over two decades of research culminated in the identification of 6PPD-quinone, an ozonated transformation product of the tire additive 6PPD, as the causative agent of mortality. Concentrations eliciting acute mortality in coho salmon occur in the parts per trillion range and within hours of exposure, making it one of the most toxic chemicals ever described. Confoundingly, effects on other salmonids are highly species and life-stage dependent, hindering assessment of the ecosystem-wide impacts of this pervasive pollutant. Global research efforts are underway to identify the mechanisms of toxicity for 6PPD-quinone and inform the molecular structures for potential alternative antiozonants for tires. Identification of less toxic tire additives are a critical goal for the protection of vulnerable salmonid population and future production of tires with greener chemistry.