Combined toxicity effects of virgin/aged polyacrylonitrile microfibers and copper on fish Carassius auratus gibelio

The widespread production and use of plastic products have highlighted the ecological risks of microplastics (MPs). MPs, mainly as microfibers (MFs), can carry various pollutants, and their properties may change over time, potentially affecting their interactions with pollutants. This study aims to compare the combined toxicity effects of virgin and aged MFs with the common heavy metal copper (Cu). Gibel carp Carassius auratus gibelio were exposed to 1 mg/L of virgin and aged polyacrylonitrile MFs (PanMfs) separately and in combination with Cu (0.5-mg/L copper sulfate) for 21 d. Results show that both aged and virgin PanMfs significantly reduced Cu accumulation in gibel carp, with no notable difference. Cu adversely affected the carp's intestine and liver, while PanMfs alone had minimal histological impact but notably mitigated intestinal damage caused by Cu. Enzyme activity and gene expression analysis indicated that both PanMfs and Cu exposure, alone or combined, compromised gibel carp's antioxidant capacity, digestive and liver functions, induced inflammation, and affected liver metabolism and intestinal immune response. Integrated biomarker response analysis of enzyme activity and gene expression showed that combined Cu and PanMfs exposure had a stronger impact on gibel carp than individual exposure. However, whether exposed individually or in combination, aged PanMfs had a slightly greater impact than virgin PanMfs. This study showed that PanMfs alone exhibit minimal toxic effects on gibel carp but significantly modify Cu toxicity, with negligible differences between aged and virgin PanMfs except for slight disparities in enzyme activity and gene expression.