Size-dependent ecotoxicological impacts of tire wear particles on zebrafish physiology and gut microbiota: Implications for aquatic ecosystem health

The ecological impact of tire wear particles (TWP), a significant source of microplastics pollution, is increasingly concerning, especially given their potential effects on the health of aquatic ecosystems. This study investigates the size-dependent ecotoxicological responses of zebrafish (Danio rerio) to TWP exposure, focusing on physiological, metabolic, and microbial community impacts over a 15-day exposure period followed by a 15-day excretion period. Through integrated analysis of gut microbiome composition, liver transcriptomics, and host physiological markers, we found that smaller TWP particles (< 120 μm) induced oxidative stress, evidenced by increased SOD and MDA levels, and inhibited growth by reducing body mass and gut length. In contrast, larger TWP particles (250-380 μm) caused more substantial disruptions in lipid and xenobiotic metabolic pathways, as shown by significant downregulation of key metabolic genes (acads, cpt2_1, hadhaa), and alterations in the gut microbiome, including the enrichment of pathogenic genera, such as Enterococcus and Fusobacterium, while depleting beneficial microbes like Acinetobacter and Methyloversatilis. These microbiome shifts led to a more complex and potentially pathogenic gut microbiome. Notably, zebrafish displayed adaptive resilience during the excretion period, with significant recovery in body mass and microbial composition, emphasizing the adaptive capacity of aquatic organisms to pollutants. Our findings underscore the broader ecological risks posed by TWP, the pivotal role of gut microbiota in host resilience to pollutants, and the need for comprehensive management strategies addressing emerging contaminants in aquatic ecosystems.