From metabolites to tissues: A comprehensive analysis of salinity-driven modulation of tetracycline effects in Mytilus galloprovincialis

Environmental salinity shifts, intensified by climate change, can influence the toxicity of pollutants such as antibiotics in marine organisms. In this study, specimens of the mussel Mytilus galloprovincialis were exposed for 28 days to three salinity levels (20, 30, and 40) in the presence or absence of tetracycline (TC) (1 mg/L). At the end of the exposure period, the effects were evaluated using an integrated metabolomic, biochemical, and histopathological approach. Tetracycline bioaccumulation did not differ significantly across salinities, indicating that biological effects were driven by stressor interactions rather than uptake. Metabolomic profiling showed that salinity and salinity-TC combinations had stronger impacts than TC alone. At salinity 20, mussels exhibited early oxidative stress and metabolic adjustments, along with tissue atrophy and lipofuscin buildup. Mussels at salinity 30 displayed relative physiological stability despite moderate histological changes under TC. In contrast, salinity 40 caused severe cellular damage, including membrane remodeling, lipid peroxidation, depleted antioxidants, and neurotoxic responses. The integrated multi-level analysis revealed coordinated stress responses involving oxidative stress, altered energy metabolism, and detoxification. Overall, these findings highlight salinity 30 as the optimal condition for M. galloprovincialis and emphasize the synergistic effects of climate-driven salinity changes and antibiotic pollution, underscoring the need to account for abiotic stressors in ecotoxicological assessments.