Weathering-modulated gut-liver toxicity of tire wear particles in zebrafish: Source-specific effects and multi-omics insights

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Tire wear particles (TWPs) are pervasive microplastic pollutants whose hazard varies with environmental weathering and emission source. Here, we investigated how water leaching modifies the physicochemical properties of TWPs from heavy-duty (HTWPs) and light-duty (LTWPs) tires and assessed both particle-associated effects in adult zebrafish and leachate-mediated developmental toxicity in embryos ( Danio rerio ). Simulated leaching increased surface roughness and oxygenated functional groups and mobilized Zn, with stronger release from HTWPs. Under a phase-separation design in which leachates were removed, pristine particles induced more pronounced systemic toxicity in adult fish, including impaired growth and organ function, oxidative stress, gut dysbiosis, and activation of immune, apoptotic, and xenobiotic metabolism pathways, whereas leached particles showed attenuated particle-associated effects. Embryonic exposure to graded leachates caused concentration-dependent cardiotoxicity, delayed hatching, and developmental defects, with HTWP leachates more strongly disrupting mitochondrial function and phototransduction than LTWP leachates. Multi-omics analyses consistently indicated lower systemic stress in leached-particle groups yet persistent developmental hazards in the dissolved phase. Accordingly, environmental risk reflects the combined and context-dependent contributions of aged particles and their coexisting leachates, and remains strongly source-dependent (HTWPs > LTWPs). These findings clarify how weathering redistributes, rather than simply reduces, TWP toxicity and should inform ecological risk assessment and management of non-exhaust vehicular emissions.