Forms of Cd, Pb, Zn and Cr in contaminated soils from Raiwind, Lahore, Pakistan

The metals Cd, Ph, Zn and Cr occurring in the area of Raiwand (Lahore), whi ch has been subjected to severe metal contamination due to municipal solid waste, were studied via sequential extraction analyses. Concentrations of t he metals ranged from background levels to levels well in excess of the max imum tolerable limits in agricultural soils. Concentrations of Cd ph, Cr an d Zn ranged from 0.2 to 70, 2.6 to 640, 4.7 to 1134 and 8.4 to 300 mg/kg of soil respectively. Higher amounts of noresidual fractions of Cd, Pb, Cr an d Zn ranged from 59 to 88.5, 60 to 89, 51 to 83, 35 to 81 percent of contam inated soil, respectively. Assuming that mobility and bioavailability bf th ese metals are related to their solubility and geochemical forms, and decre ase in the order of extraction sequence, the apparent mobility and potentia l bioavailability for these four metals in the soils decrease in the order: Pb > Cd > Cr> Zn.