Effect of vacuum UV and UV-C treatment on degradation and ecotoxicity of tire wear microrubber leachates

Tire wear microrubber particles (TWMP) are a major source of environmental contamination. Degradation of TWMP is slow and leachates contain toxic constituents including heavy metals, polycyclic aromatic hydrocarbons (PAHs) and organic additives. Few studies have addressed methods to mitigate the potential ecotoxicity of TWMP leachates. This study investigated the effects of UV-C (254 nm) and combined UV-C and vacuum UV (185 nm) treatment (VUV-UV-C) of TWMP leachates on degradation and ecotoxicity. VUV-UV-C treatment mitigated dissolved zinc and degraded the TWMP constituents fluoranthene, pyrene and benzo(a)pyrene by up to 90%, and the additives benzothiazole and phthalates by up to 70%. The potential ecotoxicity and genotoxicity of TWMP constituents were examined before and after UV treatment in bioassays with Escherichia coli, the luminescent bacterium Aliivibrio fischeri, the microalga Raphidocelis subcapitata and the crustacean Daphia magna. VUV-UV-C treatment decreased the potential ecotoxicity up to five-fold as indicated by changes in median effective concentrations (EC50). This was likely due to the formation of less toxic and less bioavailable transformation products. The VUV-UV-C treatment did not require the addition of oxidants or catalysts, and the study indicated a potential of VUV-UV-C as an advanced oxidation process to mitigate toxic compounds in TWMP leachates from urban or industrial sources.