Benzothiazoles as Molecular Markers for Automobile Tire Derived Inputs: Occurrence and Phase Distribution in Highway Runoff and Road Dust

Over the past several decades, discharges of both wastewater and stormwater have been identified as one of the major causes of the deterioration observed in receiving waters (Lamprea and Ruban, 2011). The major sources are vehicle emissions, motor oil, tyre and brake wear, and road particles in urban environments. During rainfall events contaminants are washed into the stormwater system and then discharged. The Italian legislation (Legislative Decree no. 152 of 11 May 1999) provides a complete program for the protection of water bodies from pollution. The decree implements the community directive 91/271/EEC concerning the treatment of urban wastewater, that constitutes the reference standard for the EU member states. The Italian law focuses on the quality of the receiving water body with several monitoring activities for determining the environmental damage. Despite these steps forward, several pollutants are not determined and their impact and fate in the environment are unknown. Furthermore, a comprehensive determination of contaminants of emerging concern (CECs) is crucial to understand the distribution of target compounds in dissolved phase and suspended particulate matter (Feltracco et al., 2022). The accumulation of road dust itself also serves as a notable pollutant source because it can be transported by runoff, and the associated pollutants could adversely affect the water ecosystem. Among the hazardous pollutants in dissolved phase, suspended particulate matter and road dust particles originating from tires, rubbers, and microplastics are often observed (Rosso et al., 2022), together with benzothiazoles. A total of eight benzothiazoles were determined in highway stormwater runoff and road collected from February to April 2022 near Venice (Casale sul Sile, Veneto Region, Italy). A full validated method is presented, by using an ultra-high pressure liquid chromatography coupled to a triple quadrupole mass spectrometer. The target compounds were determined in both dissolved phase and suspended particulate matter of runoff. The road dust samples were divided in seven fractions depending on particles diameters to evaluate the fraction partitioning. The results underline that SO₃H-BTH was the most concentrated benzothiazole derivate in all the analysed substrates, suggesting the presence of tires debris as main source because it is used in the vulcanization processes. The three major compounds in the dissolved phase were inversely correlated with precipitation amount and positively correlated with the number of days after last rain event, while no correlation were found with suspended particulate matter. The road dust samples indicated a clear trend of the majority of benzothiazoles to distribute in the finest fraction (<63 µm). The distribution of 2-SCNMeS-BTH was opposite to the other benzothiazoles, suggesting a different source and environmental behaviour.