FATE OF CADMIUM TOXICITY IN RIVER BED

Abstract

Heavy metals added to a river system by natural or anthropogenic sources during their transport are distributed between the aqueous phase, suspended and bed sediments. The tightly bound ions settle to bottom in due course of time subsequently. Due to changing conditions of the river ecosystem, the remobilization of ions takes place from the sediments. In the natural conditions of river water, suspended load and sediments have the important function of buffering the higher metal concentration of the water particularly by adsorption or precipitation. In the present study the adsorption characteristics of the bed sediments collected from the River Solani in western Uttar Pradesh (Now Uttranchal) India, have been analysed for the uptake of cadmium ions to visualize the traveling pattern towards ground water. A 45 cm. core sample was analyzed to study the traveling pattern of cadmium in to the bed of river Solani. The parameters controlling the uptake viz. initial metal ions concentration, the solution pH, sediment dose, contact time and particle size have been evaluated. The adsorption of metal ions increases with increasing initial metal ion concentration. The adsorption of cadmium ions on the bed sediments follows two phases: a linear phase of adsorption. and then a quasi- equilibrium state (almost flat plateau). The quasi-equilibrium state was attained within 45 min. for cadmium ions. It is observed that the extent of adsorption increases with increase of pH of the solution iii and metal ions concentration decreases with increases in pH value. Further, the adsorption of metal ions increases with increasing adsorbent doses and decreases with adsorbent particle size. The geochemically important elements such as Fe and Mn have also been determined in 0-210 pun fraction of depth upto 45 cm of the core sample. The adsorption data of the cadmium ions has been analyzed with the help of the Langmuir and Freundlich models to evaluate the mechanistic parameters associated with the adsorption process, viz. monolayer capacity and sorption intensity. It is inferred from the work that travel of heavy metal ions towards ground water is significantly halted through benthic sediments and these sediments could be utilized as local media for polishing treatment of industrial waste waters where specific heavy metal removals become necessity.