Biomonitoring of mercury and selenium in commercially important shellfish: Distribution pattern, health benefit...

This study aims to explore the concentrations of Se and Hg in shellfish along the Gulf of Mannar (GoM) coast (Southeast India) and to estimate related risks and risk-based consumption limits for children, pregnant women, and adults. Se concentrations in shrimp, crab, and cephalopods ranged from 0.256 to 0.275 mg kg^-1, 0.182 to 0.553 mg kg^-1, and 0.176 to 0.255 mg kg^-1, respectively, whereas Hg concentrations differed from 0.009 to 0.014 mg kg^-1, 0.022 to 0.042 mg kg^-1 and 0.011 to 0.024 mg kg^-1, respectively. Se and Hg content in bamboo shark (C. griseum) was 0.242 mg kg^-1 and 0.082 mg kg^-1, respectively. The lowest and highest Se concentrations were found in C. indicus (0.176 mg kg^-1) and C. natator (0.553 mg kg^-1), while Hg was found high in C. griseum (0.082 mg kg^-1) and low in P. vannamei (0.009 mg kg^-1). Se shellfishes were found in the following order: crabs > shrimp > shark > cephalopods, while that of Hg were shark > crabs > cephalopods > shrimp. Se in shellfish was negatively correlated with trophic level (TL) and size (length and weight), whereas Hg was positively correlated with TL and size. Hg concentrations in shellfish were below the maximum residual limits (MRL) of 0.5 mg kg^-1 for crustaceans and cephalopods set by FSSAI, 0.5 mg kg^-1 for crustaceans and 1.0 mg kg^-1 for cephalopods and sharks prescribed by the European Commission (EC/1881/2006). Se risk-benefit analysis, the AI (actual intake):RDI (recommended daily intake) ratio was > 100%, and the AI:UL (upper limit) ratio was < 100%, indicating that all shellfish have sufficient level of Se to meet daily requirements without exceeding the upper limit (UL). The target hazard quotient (THQ < 1) and hazard index (HI < 1) imply that the consumption of shellfish has no non-carcinogenic health impacts for all age groups. However, despite variations among the examined shellfish, it was consistently observed that they all exhibited a Se:Hg molar ratio > 1. This finding implies that the consumption of shellfish is generally safe in terms of Hg content. The health benefit indexes, Se-HBV and HBVse, consistently showed high positive values across all shellfish, further supporting the protective influence of Se against Hg toxicity and reinforcing the overall safety of shellfish consumption. Enhancing comprehension of food safety analysis, it is crucial to recognize that the elevated Se:Hg ratio in shellfish may be attributed to regular selenoprotein synthesis and the mitigation of Hg toxicity by substituting Se bound to Hg.