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Sex- and size-dependent impacts of tire wear particles and zinc oxide nanoparticles on adult zebrafish: integrated evidence from physiology, gut microbiota networks, and hepatic transcriptomics
Summary
Tiny bits of tire dust and zinc nanoparticles (found in sunscreens and other products) that wash into rivers and lakes can harm fish, and this study found that smaller particles and combinations of pollutants caused more damage—especially in females—by disrupting gut bacteria and liver function. While this research was done in zebrafish, it's a warning sign: as tire particles and nanoparticles increasingly pollute our water systems, their combined effects may be more harmful than scientists previously realized, and sex differences in vulnerability deserve more attention in pollution research overall.
The co-occurrence of tire wear particles (TWPs) and engineered nanoparticles in aquatic environments raises concerns about their combined impacts on freshwater biota. Here, we assessed sex- and size-dependent responses of adult zebrafish following 15-day exposure to control conditions, ZnO-NPs (760 μg/L), large TWPs (LTWPs, 250-380 μm; 10 mg/L), small TWPs (STWPs, <120 μm; 10 mg/L), and co-exposure treatments combining ZnO-NPs with either LTWPs or STWPs. Across endpoints, females were more sensitive than males, showing broader reductions in growth-related and organ-somatic indices. Small TWPs generally induced broader and stronger adverse effects than larger TWPs, and combined exposure to TWPs and ZnO-NPs was associated with stronger physiological and oxidative-stress responses in selected endpoints, particularly in females. Gut microbiota analyses revealed sex-dependent community restructuring, with the female co-exposure group showing a more fragmented interaction network. Female hepatic transcriptomics revealed a graded molecular response across the selected exposure scenarios, characterized by a shared stress-response core together with exposure-specific signatures related to innate immune regulation, apoptosis, proteostasis, and mitochondrial bioenergetic remodeling. WGCNA of the female hepatic transcriptome identified an immune-associated hepatic module that covaried with exposure-responsive gut bacterial genera, which were further associated with antioxidant responses and reduced body or liver weight, supporting coordinated, correlation-based multi-organ and microbiota-associated signatures under particulate stress. Collectively, these findings highlight the importance of particle size, co-exposure context, and sex-specific susceptibility in shaping the toxicity of traffic-derived particulate contaminants in freshwater organisms.