Ecological risk from heavy metals in Ennore estuary, South East coast of India

The dynamic coastal and marine waters are frequently polluted by metals that affect the biota. Metal concentrations in the biota, water and sediments of Ennore estuary were monitored spatially over two years to understand their potential impact and ecological risk. Variations in concentrations of chromium (Cr), copper (Cu), cadmium (Cd), lead (Pb) and nickel (Ni) were observed in water, sediment and marine organisms. The metal concentrations (μg/l) in the water were in the order of Ni (35) > Pb(16.9) > Cu(15.8) > Cr(12.5) > Cd(5.6) and sediment (μg/g) was Cr(390) > Pb(266) > Cu(162) > Ni(125) > Cd(7.6). Elevated metal levels in the ambient water and sediment tend to accumulate in the marine organisms. Average concentrations of Cr, Cu, Cd, Pb and Ni in fish Mugil cephalus measured as 4.6, 2.4, 2.21, 4.9 and 2.6 μg/g, 11.4, 22.1, 3.3, 8.9 and 6 μg/g in Crab Scylla serrata, 13, 20.8, 1.3, 7.9 and 4.8 μg/g in Oyster Crassostrea madrasensis and 18.8, 20.1, 1.0, 12 and 5.6 μg/g in polychaete Eunice spp. Distinct patterns of metal content in crab, oyster and polychaete (Cu > Cr > Pb > Ni > Cd) and in fish (Pb > Cr > Ni > Cu > Cd) are due to differences in their habitat and specific uptake and elimination capacity. Environmental quality indices (EQI) and Potential ecological risk index (PERI) were derived from the metal concentration in sediment. EQI evidenced that the Ennore estuary is highly contaminated by Cd and Pb from anthropogenic sources. PERI implied that the estuary is under considerable ecological risk from metals. Contamination and risk from metals are relatively higher during summer owing to the low influx of water and higher residential period. Metal concentrations are exceeding the guideline values in the ambient water, sediment and biota in Ennore estuary. It is concluded that long-term monitoring of metal distribution, bioaccumulation and risk assessment provides reliable data and valuable information for possible pollution management strategies in Ennore estuary.