Potentially Lethal Concentrations of 6PPD-Quinone Occur in Endangered Species Act Listed Aquatic Habitats of Central California

Abstract

Roadway runoff is the major source of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPDQ), a tire rubber-derived transformation product that causes acute mortality in some salmonid species. Despite its widespread occurrence, little data exist for watersheds that are Endangered Species Act (ESA) listed as critical habitat for populations of coho salmon (Oncorhynchus kisutch) and coastal rainbow trout (Oncorhynchus mykiss irideus) that are acutely susceptible to 6PPDQ. Here, we quantified 6PPDQ during a storm event across high-risk, roadway-impacted watersheds in Central California, sampling six roadway outfalls, fourteen creeks or rivers, and two estuaries. Median 6PPDQ concentrations in outfall (n = 9), creek (n = 48), and estuary (n = 2) samples were 350, 62, and 1.9 ng/L, respectively. 6PPDQ was detected in 98% of samples, with 78% of storm samples exceeding the EPA Acute Aquatic Life Screening value (11 ng/L) and 69% exceeding 24-h LC50 values for juvenile coho salmon. Concentrations peaked early during the storm and correlated significantly with traffic intensity (R2 = 0.50, p < 0.005), highlighting the chemical loading potential of busy roads. These data document high and sustained concentrations of 6PPDQ within multiple ESA-listed critical habitats, underscoring the need for improved source control to prevent possible mortalities of susceptible species within these watersheds.