Individual and combined effects of dichlorvos and nano-polystyrene on oxidative stress and biochemical parameters in the freshwater fish Barbus sharpeyi

This study investigated the individual and combined toxic effects of dichlorvos and nano-polystyrene (PS-NPS) on oxidative stress biomarkers and biochemical parameters in the freshwater fish Barbus sharpeyi . A total of 540 fish were allocated to nine treatment groups in a 3×3 factorial design with triplicate tanks. Fish were exposed for 21 days to sub-lethal concentrations of dichlorvos (0, 5, and 10 μg/L) and PS-NPS (0, 50, and 100 μg/L). Dichlorvos exposure significantly altered enzymatic activities, whereas PS-NPS exerted milder effects; however, co-exposure revealed pronounced synergistic interactions. Notably, dichlorvos and PS-NPS, alone or combined, reduced butyrylcholinesterase (BChE) activity. Their combined exposure also decreased total protein, albumin, and globulin, while elevating glucose and creatinine levels. Significant alterations were observed in superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), malondialdehyde (MDA), total antioxidant capacity (TAC), and glutathione (GSH) across fish tissues. Dichlorvos alone enhanced SOD, GPx, and GR in hepatocytes but reduced GSH and increased MDA. In gills, all treatments suppressed antioxidant defenses and elevated MDA, whereas co-exposure in kidneys increased both antioxidant enzymes and MDA while reducing GSH. Raman spectroscopy confirmed the co-accumulation of dichlorvos and PS-NPS in the liver, where combined exposure induced synergistic structural damage to proteins, lipids, and DNA. Overall, these findings highlight the heightened toxicity of pollutant mixtures compared to individual exposures, underscoring the need to consider combined contaminant effects in aquatic ecosystems.