Time and contamination level dependence of metal bioaccumulation and multibiomarker responses in fish: implications for biomonitoring

This study evaluated how different levels of sediment metal contamination (ranging from below to above toxicity thresholds) and exposure durations (3-14 days) influence metal bioaccumulation and biomarker responses in fish under estuarine conditions. Using an integrated biomarker approach, the relationships among environmental contamination, metal accumulation, and fish health were examined to improve biomonitoring strategies. At the highest contamination level, 100% mortality was observed. Under low contamination, fish eliminated excess Cu, Zn, and Hg, whereas moderate contamination resulted in progressive accumulation of Cu and Zn; Pb accumulated under both exposure levels. Early biomarker responses included decreased GSH, inhibited GPx, increased lipid peroxidation, histopathological liver lesions, and neurotoxicity, followed by partial recovery. DNA damage increased over time and across contamination levels, likely due to impaired antioxidant defenses and/or direct metal-DNA interactions. Histopathological alterations were more strongly associated with sediment contamination than with tissue concentrations, indicating that body burdens may not fully represent exposure. GSH depletion and DNA damage were the most consistent biomarkers, whereas LPO and histopathology were sensitive primarily at early exposure stages. These findings reinforce the importance of considering both exposure duration and contamination level when interpreting biomarker responses and highlight the limitations of short-term or single-biomarker assessments. Biological effects detected at low to moderate contamination support the need for more precautionary sediment-quality thresholds. Overall, integrating biochemical, physiological, and histological biomarkers provides early detection of sublethal effects and a comprehensive assessment of ecosystem health. Consequently, a multibiomarker framework represents a powerful tool to strengthen the monitoring, evaluation, and management of aquatic environmental quality.