Abstract
Four rivers viz., the Buriganga, the Turag, the Sitaluxma and the Kheru of Bangladesh linked to social, economical and cultural importance were selected with a view to observing the pollution profile of those rivers compartments and identify the pollutants, especially the deposited neurotoxic heavy metals and its dynamism or accumulation from water and sediment to different tissues of important fish species. Four sampling sites were selected along the rivers based on its importance where samples were collected during dry and wet seasons over a period of 2006 to 2006. Physicochemical and bacteriological water quality parameters including the concentrations of heavy metals in water, sediments and different organs of fish species were evaluated through standard scientific procedures. Considering all criteria for the assessment of water toxicity in investigated rivers, most of the physicochemical parameters especially DO, BOD, COD, Cl, turbidity, color, dissolved CO2 and Faecal Coliform values normally used as indicators of water pollution were in extreme hazardous point that might hamper the safe aquatic and human life because of a high organic and inorganic deposition in water resulting from high discharge of river surrounding city and industrial wastes while the pH, TSS, hardness, PO4, NO3, TDS and EC values were below the standard limit. The recorded values showed that river water quality parameters, heavy metals contents in different river compartments and accumulation in different organs of fish species (gill, liver, kidney, tail, s. bladder, ventral and upper tissue) varied significantly among the rivers, river compartments (water and sediment), fish species and fish organs and also in the seasons for river compartments. In both seasons, more accumulation tendency of Cd, Pb, Zn and Cu concentrations was mostly high in liver, gill, kidney and ventral tissue of the investigated fish species of rivers. With a few exceptions, Cd and Pb levels of the investigated fish species exceeded the permissible limit in both seasons which could be unsafe for human consumption. On the contrary, Zn and Cu contents of the investigated fish species were below the permissible limit during the study period. With a few differences, Cd and Pb levels of the investigated river waters were higher than the recommended level during dry season although all the studied metals at wet season were below the permissible limit. In both seasons, Cd, Cu, Zn and Pb levels of all the sediments of rivers were within the permissible limit except some samples of the Buriganga and the Kheru rivers. The degree of pollution of the rivers in respect of its quality parameters was Buriganga > Turag> Sitaluxma > Kheru. Sometimes, the Kheru river located at up coming industrial zone Bhaluka showed higher alarming concentrations of pollutants in water, sediments and fishes than other rivers. The critical scrutiny and appraisal of relevant data revealed that the water and fish species of the investigated rivers were highly polluted which required applying regulatory and environmental measures to put in place for ensuring the safety of aquatic life as well as human health.