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.

Stormwater exposure can cause acute mortality of coho salmon (Oncorhynchus kisutch), and 6PPD-quinone (6PPD-Q) was identified as the primary causal toxicant. Commercial standards of 6PPD-Q recently became available; their analysis highlighted a systematic high bias in prior reporting concerning 6PPD-Q. A 6PPD-Q commercial standard was used to re-confirm toxicity estimates in juvenile coho salmon and develop a liquid chromatography-tandem mass spectrometry analytical method for quantification. Peak area responses of the commercial standard were ∼15 times higher than those of in-house standards, and the updated LC 50 value (95 ng/L) was ∼8.3-fold lower than that previously reported. These data support prior relative comparisons of the occurrence and toxicity while confirming the substantial lethality of 6PPD-Q. While environmental concentrations are expected to be lower, 6PPD-Q also was more toxic than previously calculated and should be categorized as a "very highly toxic" pollutant for aquatic organisms. Isotope dilution-tandem mass spectrometry methods enabled accurate quantification (limits of quantification of <10 ng/L) within environmental samples.

Tire tread wear particles (TWP) are increasingly recognized as a global pollutant of surface waters, but their impact on biota in receiving waters is rarely addressed. In the developed U.S. Pacific Northwest, acute mortality of adult coho salmon (Oncorhynchus kisutch) follows rain events and is correlated with roadway density. Roadway runoff experimentally triggers behavioral symptoms and associated changes in blood indicative of cardiorespiratory distress prior to death. Closely related chum salmon (O. keta) lack an equivalent response. Acute mortality of juvenile coho was recently experimentally linked to a transformation product of a tire-derived chemical. We evaluated whether TWP leachate is sufficient to trigger the acute mortality syndrome in adult coho salmon. We characterized the acute response of adult coho and chum salmon to TWP leachate (survival, behavior, blood physiology) and compared it with that caused by roadway runoff. TWP leachate was acutely lethal to coho at concentrations similar to roadway runoff, with the same behaviors and blood parameters impacted. As with runoff, chum salmon appeared insensitive to TWP leachate at concentrations lethal to coho. Our results confirm that environmentally relevant TWP exposures cause acute mortalities of a keystone aquatic species.

Urban stormwater runoff is a globally significant threat to the ecological integrity of aquatic habitats. Green stormwater infrastructure methods such as bioretention are increasingly used to improve water quality by filtering chemical contaminants that may be harmful to fish and other species. Ubiquitous examples of toxics in runoff from highways and other impervious surfaces include polycyclic aromatic hydrocarbons (PAHs). Certain PAHs are known to cause functional and structural defects in developing fish hearts. Therefore, abnormal heart development in fish can be a sensitive measure of clean water technology effectiveness. Here we use the zebrafish experimental model to assess the effects of untreated runoff on the expression of genes that are classically responsive to contaminant exposures, as well as heart-related genes that may underpin the familiar cardiotoxicity phenotype. Further, we assess the effectiveness of soil bioretention for treating runoff, as measured by prevention of both visible cardiac toxicity and corresponding gene regulation. We find that contaminants in the dissolved phase of runoff (e.g., PAHs) are cardiotoxic and that soil bioretention protects against these harmful effects. Molecular markers were more sensitive than visible toxicity indicators, and several cardiac-related genes show promise as novel tools for evaluating the effectiveness of evolving stormwater mitigation strategies.