Exposure to tire particles leachates reduces clearance rate, increases trace metal accumulation and mortality, and impairs gut microbiota in mussels (Mytilus edulis).

Tire wear particles (TWPs) are a major source of microplastics in the environment, including aquatic ecosystems. Their leachates are of growing concern due to their acute toxicity on aquatic organisms. This study investigated the effects of tire leachates on mortality, clearance rate, metal accumulation, and the structure and diversity of the gut microbiota in the blue mussels (Mytilus edulis). Mussels were exposed for one and five weeks to different leachate concentrations (prepared from 5 g of new tire particles (TP) per liter) and a reconstituted metal solution reflecting the concentrations of the major metal constituents of the leachate stock solution. High-concentration exposure resulted in 61% cumulative mortality, compared to other treatments. Clear patterns of zinc, lead, and barium accumulation were observed, reaching 136.6 ± 17.3 mg Zn/kg in mussel tissues exposed to the highest concentration. High-concentration exposure also induced dysbiosis, characterized by an enrichment of anaerobic taxa (Fusobacteriales, Bacteroidales, and Clostridiales). Notably, Amplicon Sequence Variants (ASVs) affiliated with the order Francisellales, which includes lethal pathogens for mussels, were also detected at a higher proportion in the leachate treatments. After depuration, the clearance rate of mussels previously exposed to the highest leachate concentration decreased by 99%, and by 59% in mussels exposed to the metal solution. These results suggest that metals present in tire leachate contribute significantly to the impairment of mussel filtering activity.