Metal speciation in overflow and leachate from a thermal power plant ash pond - Impact on receiving waters

The speciation of six environmentally important heavy metals, viz., Fe, Mn, Cd, Cu, Zn and Ni in terms of free ions, labile complexes, slowly labile complexes and stable complexes, has been investigated in the overflow and leachates from an ash pond of a 720 mw thermal power plant in Delhi. They find their way through a canal to the receiving waters of the river Yamuna and depending on the relative concentration of the different forms of these metals in water and various sizes of suspended particulates, may have a deleterious effect on water quality. Lysimeter studies simulating the generation of ash pond leachates have also been conducted to ascertain the speciation status of metals at two different depths. It is found that the speciation is more prominent in the smallest size fraction of the particulates and therefore, ecotoxicologically more significant. There is a seasonal variation of leachability. Also, the free metal ions plus their labile complexes are more in the receiving waters than the stable complexes. This may impart metal toxicity to the water body.