Abstract

The distribution of total mercury (Hg_T) in surface sediments (0-5 cm; n = 12; particle size < 63 µm) and representative biota (benthic polychaetes, bivalve mollusks and finfish) were observed in the Sundarban mangrove wetland and adjacent regions nearby the Indian Ganges river estuary. Relatively low concentrations of Hg_T were measured in sediments ranging from 0.008 µg g^-1 to 0.056 µg g^-1. There exist sharp differences in Hg_T accumulation in biota which revealed the following decreasing trend: polychaetes > fish > bivalve mollusks. These variations are related to a number of intrinsic (size, age and sex) and extrinsic (pH and salinity) factors together with the accumulation mechanisms intrinsic to each species for mercury. An organ-specific Hg_T accumulation in bivalve mollusks was evidenced with the following decreasing order: visceral mass > siphon > adductor muscle > mantle > gill, with a maximum value of 0.42 µg g^-1 in Sanguinolaria acuminata. Fishes showed wide efficiency in Hg_T accumulation in dorsal muscle, and of most concern, one species presented Hg_T above 0.05 µg g^-1 levels, the prescribed limit established by European Union. The benthic polychaetes showed extreme variations of Hg_T in their body tissues, with the maximum value of 0.603 µg g^-1 in Dendronereis heteropoda which is above the European Union threshold value. The authors strongly recommend further monitoring to investigate the source of toxic metals, including Hg which may originate from diverse potential sources such as industrial discharges, agricultural runoff and sewage sludge from upstream of the Ganges River Estuary.

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