Unveiling the toxic mechanism of nanoscale tire wear particles to algae: The interplay of particle size, photoaging, and co-existing PFOS.

Concerns over the contamination of tire wear particles (TWPs) in freshwater ecosystems are increasing. However, the effects of size, photoaging, and co-exiting pollutants on the environmental fate and toxicity of TWPs are largely unknown. In this study, the algal growth inhibition induced by nanosized TWPs (N-TWPs) was 23.4 % greater than micro-sized TWPs (M-TWPs) at environmentally relevant concentration (1 mg/L). Photoaging significantly enhanced the algal toxicity of N-TWPs and M-TWPs by 5.6 % and 4.6 %, respectively. The presence of PFOS reduced the toxicity of N-TWPs by 24.3 %, while increased the toxicity of photoaged N-TWPs (A-N-TWPs) by 9.3 %. Mechanistically, (1) N-TWPs exhibited stronger heteroaggregation with algal cells and additive release ability as compared with M-TWPs, resulting in greater membrane damage; (2) photoaging enhanced the reactive oxygen species (ROS) generation and additive release by N-TWPs, which subsequently inducing more pronounced algal membrane damage; (3) PFOS showed a size- and aging-dependent dual role in TWPs toxicity. PFOS alleviated the toxicity of N-TWPs through adsorption and metal stabilization, whereas A-N-TWPs combined stronger PFOS adsorption with smaller particle size and enhanced membrane-disrupting ability, facilitating PFOS bioaccumulation and exacerbating algal toxicity. PLS-SEM modeling suggested that metabolic disruption and ROS generation were associated with TWPs-induced algal toxicity. These findings highlight the importance of particulate size, photoaging, and co-existed pollutants when evaluating the environmental risk of TWPs.