Occurrence of the Tire-Derived Toxicant 6PPD-Quinone in Road Dust from Unpaved Roads in a Cold-Region Urban Area

In 2021, mortalities of coho salmon were linked to 6PPD-quinone (6PPD-Q), a transformation product formed from an antioxidant in rubber tires. Since then, research concerning 6PPD-Q contamination pathways has focused on paved roads. However, over half of the road network in Canada consists of unpaved roads, which remain unstudied for 6PPD-Q contamination. In this paper, we hypothesize that (1) unpaved road networks can provide a pathway for 6PPD-Q to enter the environment and (2) 6PPD-Q concentrations in unpaved road dust are influenced by location, speed limit, collection date, and total organic carbon (TOC) content of the roads. To investigate this, we collected gravel from the surface of unpaved roads in and around Saskatoon, Saskatchewan, Canada. Chemical extractions of road dust allowed for the detection and quantification of 6PPD-Q within each sample. Concentrations of 6PPD-Q ranged between 0.207 and 1.47 ng/g of dw (median: 0.511 ng/g of dw). When normalized to TOC content, concentrations varied between 9.83 and 342 ng/g of TOC (median: 145 ng/g of TOC). No factor other than the speed limit showed a positive linear relationship with 6PPD-Q concentrations. The results of this study are an initial glimpse into the role unpaved roads play in adding 6PPD-Q into the environment.