Acute inhibitory effects of tire wear particles on the removal of biological phosphorus：The critical role of aging in improving environmentally persistent free radicals.

A comparative study explored how photoaging, ozonation aging, and Fenton aging affect tire wear particles (TWPs) and their phosphorus (P) removal in activated sludge. Aging altered TWPs' properties, increasing surface roughness, porosity, and generating more small particles, especially environmental persistent free radicals (EPFRs) in ozonation and Fenton aging. Post-aging TWPs (50 mg/L) inhibited sludge P removal significantly (p < 0.05), with rates of 44.3% and 59.6% for ozonation and Fenton aging, respectively. In addition, the metabolites involved in P cycling (poly-ß-hydroxyalkanoates: PHA and glycogen) and essential enzymes (Exopolyphosphatase: PPX and Polyphosphate kinase: PPK) were significantly inhibited (p < 0.05). Moreover, TWPs led to a decrease in microbial cells within the sludge and altered the community structure, a situation exacerbated by the aging of TWPs. P-removing bacteria decreased (e.g., Burkholderia, Candidatus), while extracellular polymeric substance-secreting bacteria increased (e.g., Pseudomonas, Novosphingobium). Pearson correlation analysis highlighted EPFRs' role in TWPs' acute toxicity to microbial cells, yet, emphasizing particle size's impact on the sludge system's purification and community structure.

Responses of colonization and development of periphytic biofilms to three typical tire wear particles with or without incubation-aging in migrating aqueous phases.

Understanding the behavior of tire wear particles (TWPs) and their impact on aquatic environments after aging is essential. This study explored the characteristics of TWPs generated using different methods (rolling friction, sliding friction, and cryogenic milling) and their transformation after exposure to environmental conditions mimicking runoff and sewage, focusing on their effects on river water and periphytic biofilms. Laboratory experiments indicate that at low exposure levels (0.1 mg/L), TWPs promoted biofilm growth, likely due to zinc release acting as a nutrient and the aggregation of particles serving as biofilm scaffolds. However, at higher concentrations (100 mg/L), TWPs inhibited biofilm development. This inhibition is linked to toxic byproducts like N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone and environmentally persistent free radicals, which reduce biofilm biomass, alter algal diversity, and decrease the production of essential biofilm components such as proteins and polysaccharides, consistent with the inhibitory behavior of TWPs on bis-(3'-5')-cyclic diguanosine monophosphate and quorum sensing signals, including acyl-homoserine lactone and autoinducer-2. Aging processes, particularly after simulated sewage treatment, further affect ecological impacts of TWPs, reducing the benefits observed at low concentrations and intensifying the negative effects at high concentrations. Contribution of here lies in systematically revealing the impact of TWPs on the development of aquatic biofilms, emphasizing the logical relationship between their aging characteristics, environmental behavior, and ecological risks. It assesses not only the release effects of typical additives and conventional size effects but also highlights the emerging photochemical toxicity (persistent free radicals), thus providing valuable insights into the aquatic ecological risk assessment of TWPs.

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

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.

Ecotoxicity of tire wear particles to antioxidant enzyme system and metabolic functional activity of river biofilms: The strengthening role after incubation-aging in migrating water phases.

Tire wear particles (TWPs) are commonly studied for their exudation toxicity, yet a critical knowledge gap exists regarding the source nature and migration of these particulate pollutants, hindering comprehensive environmental risk assessments. This study explores the pristine properties of three typical TWPs (rolling friction (R-TWPs), sliding friction (S-TWPs), and cryogenically milled tire treads (C-TWPs)) and their aging characteristics after incubation in runoff (primary aging) and sewage (further aging). Our investigation aims to unveil the intrinsic mechanisms of TWPs ecotoxicity towards freshwater biofilms. Results reveal that the generation modes significantly impact pristine physicochemical properties, including surface structure, particle size, and EPFR abundance. These factors, in turn, influence acute ecotoxicity, as evidenced by cell mortality, antioxidant enzyme activity responses, and metabolic changes in freshwater biofilms. The ecological toxicity ranking of pristine exposure groups is S-TWPs, R-TWPs, and C-TWPs, attributed to variations in surface properties and particle size. Following incubation and aging, especially in sewage, differences in physicochemical properties among TWPs types diminish. Alarmingly, ecotoxicity intensifies and becomes consistent across TWPs types, driven by the screening of small particles during water incubation aging and the formation of EPFRs on TWPs surfaces stimulated by photosensitive organic matter or groups. This study underscores the aquatic ecological risks associated with TWP surface properties, highlighting the significant influence of environmental aging conditions on these risks.