Toxic metals in finfish and shellfish along the Meghna River–estuary gradient: Deterministic and Monte Carlo probabilistic health risk assessment

Toxic metal contamination in estuarine fish and shellfish threatens food safety and public health globally, yet integrated studies examining both finfish and shellfish using deterministic and probabilistic risk models across complete estuarine gradients remain scarce in South Asia. We quantified eight toxic metals (As, Cd, Co, Cr, Cu, Hg, Ni, Pb) in four finfish and two shellfish species along the Meghna River-Estuary gradient, Bangladesh, using ICP-MS. Metal concentrations followed the order Cu > Cr > As > Pb > Ni > Hg > Co > Cd. As, Cr, Cu, Pb, and Hg exceeded FAO/WHO/EU permissible limits, with Cu (up to 21.52 mg kg-1) and Cr (up to 3.62 mg kg-1) exceeding limits by 24-fold and 103-fold, respectively. Metal Pollution Index (MPI) ranged from 0.26 (upstream Tenualosa ilisha) to 2.10 (downstream Scylla serrata), confirming downstream enrichment (downstream > midstream > upstream). Shellfish accumulated significantly higher metal burdens than finfish. Deterministic analysis revealed that estimated daily intakes remained below tolerable limits; however, target hazard quotients for Hg and As exceeded 1 in downstream samples. However, Monte Carlo simulation (10,000 iterations) revealed substantially greater risks: over 99% of finfish consumers and 83-98% of shellfish consumers face non-carcinogenic hazard, while 100% exceed acceptable carcinogenic risk thresholds (1 × 10-4), confirming that deterministic methods substantially underestimate risks. These findings are based on dry-season muscle samples, which may limit generalizability. Multivariate analysis linked As and Hg to atmospheric sources, while Pb, Cd, Cr, and Ni originated from industrial and municipal discharges. We recommend region-specific consumption advisories prioritizing children and frequent consumers of downstream seafood, alongside targeted pollution control in the lower estuary.