Heavy metal release from two typical tire microplastics under different simulated environments and bioavailability assessment in China

Little information is available on the release and associated bioavailability of heavy metals (HMs) in tire repair-polished debris (TRD) and recycled tire crumb (RTC). Thus, simulated TRD from 4 tire brands, TRD in auto repair shops and RTC in artificial turf from the northern and southern region of China were prepared to investigate HMs release under different simulated environments of acid rain and seawater and assess the associated bioavailability. The average contents of zinc (Zn), arsenic (As), and cadmium (Cd) were 11.70 g/kg, 4.54 mg/kg and 2.31 mg/kg, respectively, in the TRD and 1.85 g/kg, 6.88 mg/kg and 5.52 mg/kg, respectively, in the RTC from the northern region, which were higher than those in the southern region. A lower pH promoted Zn and Cd release from TRD and RTC but inhibited As release. Higher salinity enhanced HMs release from TRD and RTC. HMs release from RTC was greater in the northern region than in the southern region because of the higher metal content in used tires and greater aging in the northern region. Based on the solubility bioavailability research consortium, Zn was found to be nonbioavailable in both the stomach and intestinal phases despite the elevated Zn content. Conversely, As presented high bioavailability despite its low content, whereas Cd presented a low level with low bioavailability. As in TRD and RTC deserve more attention to their potential risks, particularly from Chinese northern region. Our findings can help understand HMs' release from tire microplastics into the environment and their potential risks.