Vehicle-specific toxicological profiles of tire wear particles: Physiological, microbial, and transcriptomic disruptions in zebrafish induced by light and heavy-duty vehicle emissions

Tire wear particles (TWPs) from vehicles have emerged as significant sources of environmental microplastics, releasing hazardous metals and organic contaminants into aquatic ecosystems. However, the differential toxicological effects of TWPs originating from heavy-duty vehicle tire wear particles (HTWPs) versus light-duty vehicle tire wear particles (LTWPs) remain inadequately characterized. Here, we comprehensively evaluated physiological responses, gut microbiota alterations, and liver transcriptomic changes in zebrafish exposed to HTWPs and LTWPs. Scanning electron microscopy (SEM) analysis revealed that HTWPs exhibit rougher surfaces and sharper edges compared to LTWPs. Physiologically, HTWP exposure resulted in marked reductions in body and organ growth metrics and induced sustained oxidative stress responses, whereas LTWPs triggered comparatively milder oxidative effects. Microbial analysis demonstrated significant gut dysbiosis following HTWP exposure, characterized by decreased microbial diversity and an increased abundance of pathogenic Acinetobacter, negatively correlated with hepatic irf1b expression. Functional predictions based on PICRUSt2 further revealed vehicle-specific alterations in gut microbial metabolism: immune- and xenobiotic-related pathways were enriched under HTWP exposure, while LTWP exposure enhanced microbial functions related to lipid metabolism. These functional shifts suggest potential host-microbiota metabolic crosstalk. Transcriptomic analyses indicated particle-type-specific disruptions: HTWPs predominantly impaired carbohydrate metabolism, downregulating critical glycolytic genes (pgk1, pkma), while LTWPs primarily altered lipid metabolic pathways, as evidenced by decreased acacb and increased hadhaa expression. Notably, both HTWP and LTWP exposures activated inflammatory signaling via the MAPK pathway, particularly through upregulation of mapk8a. Quantitative PCR validation confirmed the robustness and reliability of the RNA-seq results. Together, these findings highlight distinct toxicological mechanisms driven by vehicle source and underscore the need for source-specific ecological risk assessments to mitigate the environmental impact of TWP pollution.