Occurrence of benzothiazole and its derivates in tire wear, road dust, and roadside soil

Benzothiazole (BT) and its derivates are commonly used as vulcanization accelerators in rubber production. Information on the occurrence of BTs in road dust (RD) and on human exposure to these compounds is very limited. BT and its six derivates in tire wear particles (TWPs) and RD were determined in this study. Samples were extracted using solid-liquid extraction, purified by a HLB SPE column, and determined by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). All seven BTs were found in 17 TWPs samples from different tire brands. The mass fractions of all seven BTs (∑BTs) in TWPs ranged from 46.93 to 215 μg/g with an average concentration of 99.32 μg/g. Benzothiazole and 2-hydroxybenzothiazole (2-OH-BT) were the two major compounds, accounting for 56%-89% of the total. The seven BTs were also found in all 36 sets of RD samples (each set included one sample of TSP (particles < 75 μm in diameter), PM10 (particles < 10 μm in diameter) and PM2.5 (particles < 2.5 μm in diameter)) fractions of RD. The median ∑BTs concentration was highest in PM2.5 (26.62 μg/g), followed by PM10 (22.03 μg/g), and TSP (0.68 μg/g). Of the seven BTs, BT, 2-aminobenzothiazole (2-NH2-BT), 2-mercaptobenzothiazole (MBT), and 2-(methylthio)benzothiazole (MTBT) were distributed in PM2.5 and 2-OH-BT was distributed in PM2.5-10 of RD. Based on the mass fractions of BTs in the TSP, PM10, and PM2.5 fractions of RD, human exposure via ingestion, inhalation and dermal absorption were evaluated. Ingestion was found to be the main exposure pathway in humans, and daily intake of BTs in PM2.5 was highest, followed by PM10 and TSP, respectively. Children may suffer more health risks than adults when exposed to RD.