Ecotoxicity of three typical tire wear particles to periphytic biofilms: The potentiating role after natural water-incubation-aging

Abstract

Tire wear particles (TWPs), abundant in the aquatic environment, pose potential ecological risks, yet their implications have not been extensively studied. Rolling friction TWPs, sliding friction TWPs (S-TWPs) and cryogenically milled tire treads were used as research objects to study the ecotoxicity and difference of the above materials before and after aging in natural water (AS-TWPs) to the periphytic biofilm. The results showed that there were significant differences in the microstructure, surface elements, size, functional groups and environmentally persistent free radicals (EPFRs) of the three TWPs. After aging in natural water, the properties of the three TWPs mentioned above showed homogenization, but the EPFRs and reactive oxygen species (ROS) yield were different. After exposure to TWPs (10 mg L−1), total organic carbon and adenosine triphosphate decreased significantly (p < 0.05), and the production of extracellular polymeric substances (EPS) in the periphytic biofilm increased, in which the content of humic-like substance and proteins (tryptophan protein and humic acid-like substances) increased obviously. The increment of TB-EPS was higher than that of LB-EPS, and S-TWPs and AS-TWPs had the strongest promoting effect on EPS secretion. In addition, 10 mg L−1 TWPs caused massive cell death in the periphytic biofilm, which was more obvious in the S-TWPs and AS-TWPs exposure group. The toxic mechanism of TWPs promotes intracellular ROS accumulation and leads to the release of lactate dehydrogenase, which was attributed to the formation of EPFRs on the surface of TWPs and an increase in EPFRs intensity after aging in natural water. TWPs at environmentally relevant concentrations (0.1 mg L−1) had no biological toxicity to periphytic biofilms. This study fills the gap in the study of the surface structure characteristics of TWPs on the toxicity of periphytic biofilms, and is of great significance to the study of the aquatic toxicity mechanism of TWPs.