ZnO nanoparticle-mediated cadmium adsorption induces bioaccumulation, oxidative stress, and apoptotic responses in Korean rockfish Sebastes schlegelii.

Metal oxide nanoparticles (NPs) and trace metals may co-occur in polluted coastal waters, and their interactions can alter trace metal behavior and toxicity in aquatic organisms. Here, we evaluated the finteraction between zinc oxide (ZnO) NP and cadmium (Cd) and their effects on Cd accumulation and physiological responses in Korean rockfish Sebastes schlegelii. Changes in zeta potential and Cd concentrations in the supernatant were analyzed to assess ZnO NP-Cd interactions. Fish were exposed to ZnO NP at 0.5 or 5 mg/L and Cd at 10 µg/L, either individually or in combination, for 5 days. Hepatic Cd accumulation was measured, and mRNA expression of antioxidant-related genes, metallothionein (MT), and caspase-3 was analyzed in the liver and gill. Hepatic MT mRNA signals were visualized via in situ hybridization, and caspase-3 levels were measured as an indicator of apoptosis-related responses. After Cd addition, the zeta potential of ZnO NP increased, whereas Cd concentrations in the supernatant decreased, a pattern consistent with potential interactions between Cd and ZnO NP surface, including adsorption. Combined exposure was associated with higher hepatic Cd accumulation and stronger induction of antioxidant-related genes and MT mRNA than individual exposure. Hepatic MT mRNA signals and caspase-3 expression and levels were higher under combined exposure. These findings indicate that co-exposure to ZnO NP and Cd is associated with increased Cd accumulation and more pronounced antioxidant-, metal detoxification-, and apoptosis-related responses. Although underlying mechanisms require direct verification, ZnO NP-Cd interactions may alter Cd bioavailability and physiological responses in Korean rockfish.