High hydrostatic pressure modulates copper and cadmium accumulation and biomarker responses in Modiolus kurilensis: Implications for deep-sea mining risk assessment

As deep-sea mining approaches commercial implementation, evaluating contaminant risks under realistic environmental conditions-particularly high hydrostatic pressure (HP)-has become increasingly critical. Yet, most existing toxicological studies are conducted under atmospheric pressure, potentially overlooking pressure-induced modifications in metal behavior and biological response. In this 48-hour exposure study, we used the coastal mussel Modiolus kurilensis, a close relative of deep-sea Bathymodiolins, to investigate its biological responses to copper (Cu) and cadmium (Cd) exposure (100 μg/L) under both atmospheric and simulated deep-sea pressure. We assessed metal accumulation and 13 traditional metal-related biochemical biomarkers across gill, mantle, and visceral mass. Results showed that HP significantly reshaped metal accumulation in a tissue- and metal-specific manner, enhancing Cu and Cd uptake in gill and mantle, and selectively promoting Cd retention in visceral mass. Correspondingly, HP reprogrammed biochemical responses: mantle reactivity was suppressed, gill detoxification intensified, and visceral mass shifted toward lipid oxidative damage and metabolic disruption. Critically, by comparing responses across both pressure conditions, we identified two pressure-insensitive biomarkers-acid phosphatase and hexokinase in the mantle-that consistently responded to metal exposure regardless of pressure. These biomarkers hold strong potential for pressure-independent biomonitoring. In contrast, many conventional biomarkers showed divergent responses under HP, highlighting the risk of misinterpretation if pressure effects are ignored. Our study offers a pressure-aware framework for deep-sea ecotoxicology using coastal proxies and provides essential guidance for selecting reliable biomarkers for future environmental risk assessments of deep-sea mining.