Size- and duration-dependent toxicity of heavy vehicle tire wear particles in zebrafish

Tire wear particles (TWPs), as a pervasive environmental pollutant, pose significant risks to aquatic ecosystems. This study investigates the effects of small (HS) and large (HL) TWPs produced by heavy vehicles on zebrafish, focusing on physiological, microbial, and transcriptomic levels, as well as their intergenerational consequences, under short-term (15 days) and long-term (90 days) exposure. Short-term exposure to small particles (HS15) significantly reduced body width and triggered widespread oxidative stress, while long-term exposure to large particles (HL90) increased gut weight and decreased gill weight, reflecting respiratory and digestive disruptions. Tissue-level analyses revealed that smaller particles accumulated more readily in internal organs, whereas larger particles caused localized physiological stress. Gut microbiota profiling indicated a marked decline in microbial diversity, compositional shifts, and network simplification, with HL15 enriched in Acinetobacter and xenobiotic metabolism pathways, and HS15 exhibiting Proteobacteria-dominated dysbiosis and enrichment of LPS biosynthesis genes. Liver transcriptomics revealed group-specific responses: HL15 exposure activated innate immunity via the NOD-MAPK axis, while HS15 induced atypical PI3K-NF-κB signaling, potentially linked to microbial LPS. Notably, all TWP-exposed groups showed enrichment of the herpes simplex virus 1 (HSV-1) infection pathway, suggesting a conserved antiviral-like host response. Transgenerational effects were evidenced by impaired growth and significant downregulation of GH/IGF signaling and upregulation of apoptotic genes in offspring, despite only subtle transcriptomic changes in long-term exposed parents. These findings underscore the importance of particle size, exposure duration, and microbiota-gut-liver axis interactions in mediating TWP toxicity and highlight potential transgenerational risks associated with environmental microplastic exposure.