Artificial UVC-aging process aggravates the toxicity of polystyrene microplastics to zebrafish, especially females

The ecological risks of microplastics (MPs) are increasingly recognized. However, the role of the MP aging process on risks in freshwater ecosystems remains unknown. In this study, 500 nm polystyrene microplastics (PS-MPs) were subjected to artificial UVC (254 nm) irradiation for six months to induce accelerated photo-oxidation. Adult zebrafish were exposed to pristine and UVC-aged PS-MPs for 21 days to evaluate health related indicators. UVC photodegradation significantly altered the physicochemical properties of PS-MPs, including roughening of surfaces and generation of new oxygen-containing functional groups. Exposure to aged PS-MPs produced stronger biological responses than pristine particles, as indicated by integrated biomarker response (IBR) analysis, with elevated oxidative stress and changes in humoral immune indicators. Multi-omics analysis revealed that both pristine and aged PS-MPs induced gut microbiota dysbiosis and hepatic metabolic disorder, while the aged PS-MP exposure group showed broader metabolic perturbations in female zebrafish, including alterations in glycolipid and amino-acid metabolism pathways and enhanced oxidative stress responses. Correlation analysis indicated close associations among gut microbial shifts and metabolic alterations. Our results highlight the enhanced toxicity of aged PS-MPs on freshwater organisms and emphasize the importance of considering the aging process in toxicological assessments of MPs in freshwater systems.