ABSTRACT
The bioavailability of metals in soil is a dynamic process that depends on specific combinations of chemical, biological, and environmental parameters. The bioavailability, movement of metals, and their eco-toxicity to plants depend mainly on their particular chemical forms or methods of binding. Sequential extraction can be used in composts or various wastes to examine the distribution of heavy metals in different fractions. Meanwhile, it can provide a more exact degree of the environmental risk. Singh and Kalamdhad reported that the exchangeable, carbonate fraction, reducible, oxidizable fraction, and residual fraction of different heavy metals (zinc, copper, manganese, iron, nickel, lead, cadmium and chromium), their total metal contents of in sawdust, cattle manure, and water hyacinth. The composting process is highly efficient for the stabilization of waste materials and for the immobilization of heavy metals. Bioavailable fractionations of heavy metals increase during the thermophilic stage of composting, whereas these fractions are converted into less mobile fractions at the maturity of the composting.
