Combined effects of microplastics and copper on antioxidant capacity, gut microbiome, and metabolomics of Pseudorasbora parva.

Microplastics (MPs) and metal pollutants such as copper (Cu) are common pollutants in aquatic environments worldwide, posing a potential threat to the health of aquatic organisms and ecosystems. In this study, we investigated the effects of single and combined exposures of MPs (1 mg/L) and Cu (50 μg/L) on the antioxidant capacity, histopathology, gut microbiota, and metabolomics of Pseudorasbora parva which was used as a model organism. Results showed that exposure to both Cu and MPs in combination reduced Cu accumulation in tissues, mitigating the effects of Cu-induced oxidative damage. Histopathological analysis revealed that combined exposures resulted in lower levels of tissue damage than exposure to Cu alone, as evidenced by reduced leukocyte infiltration in hepatocytes, the mitigation of intestinal mucosal damage and improved gill filament epithelial cell integrity. Gut microbial community analysis showed that higher Cu concentrations significantly increased the abundance of Fusobacteriota and Cetobacterium. Metabolomics analysis revealed that in the group exposed to both Cu and MPs, compared to the Cu group, the metabolism of nucleotides, pyrimidine and glycerophospholipids was upregulated, enhancing cellular repair and defense, while the downregulation of other pathways reduced energy expenditure and prevented reaction excess. This study demonstrated that P. parva responded to multiple pollutant stress through a complex range of metabolic regulatory mechanisms, providing novel insights into the molecular response mechanisms of aquatic organisms to the combined stress of multiple pollutants, which is of great significance for aquatic ecological risk assessments.