Salinity-dependent cadmium bioaccumulation, oxidative stress, and genotoxicity in the bivalve Mactra veneriformis

Marine bivalves face combined stress from cadmium (Cd) pollution and salinity fluctuations. This study assessed salinity-dependent Cd bioaccumulation and toxicity in Mactra veneriformis exposed to five salinities (18-34) and three Cd concentrations (0.05-0.25 mg L^-1) over 7 days. We quantified Cd accumulation, bioconcentration factors (BCFs), reactive oxygen species (ROS), glutathione peroxidase (GPx), glutathione S-transferase (GST), and genotoxicity (DNA-integrity F-value) in gills and digestive gland. Cd accumulation was time- and dose-dependent, with the highest levels observed in gills. BCFs were negatively correlated with salinity in most treatments; however, at salinity 18 with 0.25 mg L^-1 Cd, gill BCF was lower than at salinity 22, suggesting potential physiological disturbance under extreme combined stress. Salinity deviation from the optimum amplified ROS production, shifted antioxidant-enzyme peak timing, and triggered late-stage GPx and GST depletion. Gills exhibited rapid but transient enzymatic responses, whereas the digestive gland showed delayed, sustained activation. The most severe genotoxicity (lowest F-value) arose in gills at salinity 18, coinciding with antioxidant defense system collapse. Overall, salinity deviation (especially low salinity) exacerbated Cd-induced oxidative and genotoxic damage, potentially via elevated Cd bioaccumulation, suggesting strong synergistic toxic interactions. These biomarker-based observations require further mechanistic validation and inform Bohai Sea ecological risk assessment and aquaculture management.