Trace metals and lanthanides in a tropical river environment

The river Periyar in the State of Kerala, India is subjected to pollution from a number of industrial units such as zinc smelter, rare earth plant, phosphatic fertilizer unit etc. The levels of Zn and Cd in water and sediments in the river have in recent years increased ten fold as compared to a study conducted earlier during 1970. The levels of these trace metals in water increase at the backwater zone under high salinity in summer due to solubilisation from the sediments. Among the lanthanides Ce is the most predominant in water. Elements such as Ce, La, Sm, Gd and Y show a concentration factor of 10³ in sediments. The trace metals show maximum concentration at the top layer of sediment column extending up to 20 cm from the surface. Particle size analysis of river sediments in the industrial outfall area shows a mass median diameter of 11 μm with a geometric standard deviation of 2.4 for Zn and Cd.