Pollution Load of Four Heavy Metals in Water, Sediment and Benthic Organisms in the Kulti River of Sundarban Fed by Metropolitan Sewage

The degree of heavy metal contamination was estimated in the river water, sediments and benthic organisms in the Kolkata metropolitan sewage outfall zone and downstream areas along the Kulti River track. Four heavy metals namely Cr, Pb, Zn and Cd were studied seasonally. The hierarchy of heavy metals in the water samples and sediments was found in the order Z>Pb>Cr>Cd and Zn>Cr>Pb>Cd respectively in most of the cases. Among the four heavy metals, Pb was found to be beyond the permissible limit recommended by Central Pollution Control Board of India for inland discharge. The extent of contamination by Cd is very prominent in the sediments followed by Pb, which is observed not only in the outfall region but also found persistent in the downstream stations. On the other hand contamination of Zn and Cr was not found to be widespread. Contamination in sediments of the outfall zone was most pronounced during the monsoon, while in the same season it was observed least in case of water samples. The pollution load index study revealed that the overall metal pollution load depleted towards the downstream. Among the two benthic organisms studied, metals were found to be accumulated more in Uca rosea than Boleopthalmus spp.