Heavy metals in biota from Sundarban Wetland Ecosystem, India: Implications to monitoring and environmental assessment

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Abstract
The coastal environment of West Bengal is recognized as the most diversified and productive ecosystem among all the maritime states of India. This area faces organic pollution from domestic sewage and toxic pollution from industrial effluents leading to serious impacts on water and sediment quality as well as on biodiversity. This article aims at providing information on concentration levels of heavy metals (iron, zinc, copper, manganese, cadmium, and mercury) in the tissues of a suspension feeder bivalve Macoma birmanica, whole body tissues of five gastropods (Cerithidea cingulata, C. obtusa, Telescopium telescopium, Thais lacera and Nerita articulata) and four finfishes (Liza tade, Harpodon nehereus, Trichiurus sp., and Boleopthalmus sp.) collected from water bodies of Sagar Island (22° 19′ N; 80° 03′ E), the largest delta of Sundarbans. A general trend with the following in decreasing order occurred: Fe>Zn>Mn>Cu>Cd>Hg. Both species-dependent variability and temporal variations were pronounced. A high degree of organ specificity was evident in M. birmanica where gill and mantle exhibited higher metal accumulation due to the ion exchange property of the mucous layer covering these organs. Gastropods and finfishes were differentially selective for a range of metals, reflecting the availability of the elements in the environment and the diet and digestive physiology of these organisms. An overall elevated concentration of these metals was observed during monsoon months when low pH and salinity prevailed in the ambient medium. A continuous monitoring program is recommended to establish the studied organisms as bioindicators and to identify future changes to conserve the “health” of this fragile ecosystem.