Total and Methyl Mercury Concentrations of Deep-Sea Fish in the East Sea, Korea: A Human Health Risk Assessment

Mercury (Hg) contamination in deep-sea ecosystems is of increasing concern due to its strong bioaccumulation potential and implications for seafood safety. However, depth-resolved information on Hg speciation and tissue-specific accumulation in deep-sea fish remains limited, particularly in semi-enclosed marginal seas such as the East Sea of Korea. In this study, total mercury (THg) and methylmercury (MeHg) concentrations were quantified in multiple tissues (muscle, liver, gill, bone, and skin) of deep-sea fish collected across a pronounced depth gradient (100–1300 m). Hg concentrations increased significantly with sampling depth (p < 0.05), indicating depth-driven enrichment processes. MeHg accounted for 61.8–87.4% of THg and predominated in muscle and liver, highlighting its toxicological relevance. Human health risk assessment based on Estimated Daily Intake (EDI) and Target Hazard Quotient (THQ) suggested that average exposure levels remained below international safety thresholds. Nevertheless, several deep-sea taxa (e.g., Lycodes tanakae and Malacocottus gibber) approached cautionary levels under high-consumption scenarios. These findings demonstrate that habitat depth is a key ecological driver of Hg accumulation in deep-sea fish and underscore the importance of depth-resolved, species-specific monitoring for effective seafood safety management as deep-sea fisheries expand.