Short-term effects of biosolid and municipal solid waste applications on heavy metals distribution in a degraded soil under a semi-arid environment.

Digested biosolid (SS) and municipal solid waste (MSW) were surface-applied to a degraded carbonated soil, under semi-arid environment, at rates of 0 and 80 Mg/ha, to determine the changes in organic matter and in the distribution of heavy metals in the topsoil, 1 year after its application. Waste application slightly increased the organic matter content and improved the composition of humic fractions in the treated soils, mainly in the MSW amended plots. A sequential extraction method (Tessier et al., 1979) was used to determine the distribution of Cd, Cr, Cu, Ni, Pb and Zn in both the waste and the amended.soils. Waste application had little effect on the total concentration of Ni and Cr in the treated soils as a consequence of the low availability of these metals in the wastes. A considerable increase of Cd, Cu, Pb and Zn was observed as a consequence of the high content and/or high availability of these metals in the wastes. The more labile fraction (exchangeable fraction) of all metals studied increased slightly (< 1.5 mg/kg) when SS and MSW were added. However, a remarkable increase in the Fe/Mn oxide fraction of Cd, Cu and Pb and in the organic fraction of Zn were noted in treated plots, this increase being higher in the MSW treated soils.