Assessment of heavy metal species in decomposed municipal solid waste

Heavy metal speciation studies on municipal solid waste samples collected from Kodungaiyur dumpsite in Chennai, India, were carried out for Cu, Ni, Pb, Zn, Cr, Fe, Mn and Cd. Three samples were collected at depths of 0-1 m, 1-2 m and 2-3 m, and analyzed. X-ray diffraction studies showed the presence of montmorillonite, illite, quartz and calcium carbonate minerals. The Tessier method was used to fractionate the metal content into exchangeable, acid extractable, reducible and oxidizable fractions. Residual and total metal contents were determined in the aqua regia digest. Iron was the major metal constituent (20g kg^-1) while the lowest metal concentration was found for cadmium (3mg kg^-1). Descending order of the average total metal contents for these three depth levels was Fe, Cu, Zn, Cr, Mn, Pb, Ni and Cd. The bioavailable fraction (exchangeable and acid extractable fractions) comprised less than 40% of the total metal content for all the metals studied, except Cd. Most of the Fe and Cr were found to be associated with the residual fraction, which is almost inert. Based on the average of absolute values for the three depth levels, the bioavailability order of metals is Zn>Mn>Pb>Ni>Cu>Fe>Cr>Cd. Recovery obtained by comparing the aqua regia extracted metal content with the sum of sequentially extracted fractions was in the range of 91-110%.