Heavy Metal Distribution and Bioavailability in Coal Ash and Sludge Amended Acid Lateritic Soil Under Field Conditions

Abstract

Chemical fractionation of heavy metals in ash, sludge and amended soil was performed using sequential extraction. The metals were predominantly found to be present in the residual and carbonate fractions in the native soil and ash while amounts of Ni, Cd and Zn were significant in the exchangeable fractions of sludge. The distribution of metals in the extractable fractions differs according to the metal extracted, the treatment and the proportions of application. Among the metals, Ni and Zn and to a lesser extent Cd moved readily in the sludge amended soils due to lowering of pH and simultaneous increases in their most labile forms. Better yields of paddy and peanut with ash addition and reduction with sludge proportion were observed. The paddy straw and peanut shoot showed the maximum accumulation of metals indicating a physiological barrier in the transfer of metals from the shoot to the grain. Linear relationships were observed between the soil total metal concentrations with that in the crops. The study indicated that at the applied rate, the behavior of heavy metals in the amendments was primarily controlled by sludge.