|dc.description.abstract||Road traffic emissions are known to contribute in environmental pollution and have adverse effects on humans. The emissions of organic and inorganic pollutants from traffic and road activity are established as the primary source of contamination in an urban environment. Abrasion of road materials, and tire and break wear are only some of thee contributing pollution factors in a road setting. Therefore, road dust is a promising environmental matrix for investigating sources of urban pollution. The road dust is a complex matrix composed of both natural and anthropogenic materials, and is a heterogeneous mix originating from diverse sources. Therefore, it is a great need for better characterization of the road dust, and a particularly need of good chemical markers for tire and brake wear.
In this study, a liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous determination of six benzothiazoles (BTHs) and seven benzotriazoles (BTRs) primarily in road dust. The target benzothiazoles were benzothiazole, 2-hydroxy-benzothiazole, 2-mercaptobenzothiazole, 2-methylthio-benzothiazole, 2-amino-benzothiazole, and 2-Morpholin-4-yl-benzothiazole, and the target benzotriazoles were benzotriazole, 1-hydroxy-benzotriazole, 4-methyl-1H-benzotriazole (tolyltriazole), 5,6-dimethyl-1H-benzotriazole (xylyltriazole), benzotriazole-5-carboxylic acid, 5-chloro-1H-benzotriazole and 5-amino-1H-benzotriazole. Benzothiazoles and benzotriazoles are known pollutants in an urban environment. Benzothiazoles are previously proposed as potential chemical markers of tire wear, while benzotriazoles are well established anticorrosive chemicals linked to metal pollution. In addition, 66 elements were measured in the road dust samples by ICP-MS analysis in order to account for inorganic pollution sources.
The road dust samples analysed in this study were collected using a novel sampling instrument for road dust, the Wet Dust Sampler. Road dust samples were taken from both the non-studded tire season (summer) and the studded tire season (winter). The turbid road dust samples were filtered, extracted by sonication and prepared using solid phase extraction. In an attempt to pinpoint road dust pollution sources, different sample matrices were collected and analysed. In addition to road dust samples, air filters, tires, core-samples from asphalt, bitumen and background soil sample were analysed for both elements and/or organics. The tire samples, the asphalt samples, and the asphalt binding agent were also extracted by sonication and liquid extraction.
The concentrations both benzothiazoles and benzotriazoles and elements were higher in the winter season compared to the summer season. The concentrations of the benzothiazole and benzotriazole derivatives differed in the summer and winter season, indicating different transformation ratios based on season. Higher concentration of BTHs in the winter was probably attributed leaching from winter tires, possibly affected by road salt. This is described with a simple steady state kinetic model/equation in this study. The major source of most elements in road dust is the minerals in the coarse aggregate used in the pavement, and/or wear of car parts (chassis, shocks, brakes). The concentration of antimony (Sb) was approximately the same for both sampling seasons in dust, and it was associated to break wear. The increase in benzotriazoles, mainly tolyltriazole (TTR), in the winter season was probably attributed to the increased wear of car parts affected by road salt.
Making use of principal component analysis (PCA) it was possible to group adequately the sample matrices that were analysed. The PCA indicated associations between break wear and tire wear. 2-S-BTH and Sb were proposed as effective markers of break and rubber tire wear, while 2-OH-BTH, 2-Me-S-BTH, and Cl were proposed as possible markers of chemical leaching from tire rubber.||