Occurrences of Tire Rubber-Derived Contaminants in Cold-Climate Urban Runoff

Abstract

Recent findings that 2-anilo-5-[(4-methylpentan-2-yl)amino]cyclohexa-2,5-diene-1,4-dione (6PPD-quinone), the transformation product of a common tire rubber antioxidant, is acutely toxic in stormwater-impacted streams has highlighted the need for a better understanding of contaminants in urban runoff. This study represents one of the first reports of 6PPD-quinone and other tire rubber-derived compounds in stormwater and snowmelt of a cold-climate Canadian city (Saskatoon, 2019-2020). Semiquantification of the five target compounds, N,N′-diphenylguanidine (DPG), N,N-dicyclohexylmethylamine (DCA), N,N′-dicyclohexylurea (DCU), 1-cyclohexyl-3-phenylurea (CPU), and 6PPD-quinone, revealed DPG was most abundant, with average concentrations of 60 μg L-1 in stormwater and 1 μg L-1 in snowmelt. Maximum observed concentrations of DPG were greater than 300 μg L-1, equivalent to loadings of 15 kg from a single rain event. These concentrations of DPG represent some of the highest reported in urban runoff globally. 6PPD-Quinone was detected in 57% (12/21) of stormwater samples with a mean concentration of approximately 600 ng L-1 (2019) and greater than 80% (28/31) of snowmelt samples with mean concentrations of 80-370 ng L-1 (2019 and 2020). Concentrations of 6PPD-quinone exceeded the acute LC50 for coho salmon (0.8-1.2 μg L-1) in greater than 20% of stormwater samples. Mass loadings of all target chemicals correlated well with roads and residential land-use area.