Occurrence, spatial distribution, and risk assessment of mercury in bivalves from a human-impacted Tropical Atlantic...

This study evaluated mercury (Hg) contamination in three bivalve species: Anomalocardia flexuosa, Crassostrea rhizophorae, and Mytella guyanensis. The samples were collected from 11 sites across Todos os Santos Bay (BTS), Bahia, Brazil. Mercury quantification was performed using a Direct Mercury Analyzer (DMA-80) and validated with certified reference materials DORM-4 (fish protein) and 2976 (mussel tissue). Concentrations ranged from 0.028 to 0.199 mg kg^-1, remaining below Brazilian (0.5 mg kg^-1) and international (1.0 mg kg^-1) limits for human consumption. Although interspecific differences were minor, significant spatial variation was observed, with higher Hg concentrations in the western bay, likely influenced by strong tidal influence governing water circulation in the bay. Human health risk assessment based on Estimated Weekly Intake (EWI), Target Hazard Quotient (THQ), and Maximum Safe Consumption Quantity (MSCQ) indicated that regular consumption of these bivalves poses a low health risk, with EWI values below 40 % of the Provisional Tolerable Weekly Intake and THQ < 1. Ecological risk indices calculated from sediment Hg concentrations, including the Contamination Factor (CF), Ecological Risk Index (Er), and Geoaccumulation Index (Igeo), revealed low ecological risk at most sites, with moderate contamination detected only at Ribeira, an area historically impacted by industrial discharges. Overall, the findings provide essential baseline data for seafood safety management and environmental monitoring in Todos os Santos Bay.