Samples of A and B horizons of a humic red-yellow latosol with a clayey texture were incubated in salt solutions of Cd, Cr, Cu, Ni, Pb and Zn under greenhouse conditions at the Universidade Federal de Viçosa, Brazil, from March to September 1994. The main objectives were to adapt a method for fractional extraction of metals and to evaluate their behavior in soluble, exchangeable, bound to organic matter, bound to Al oxides, bound to Fe oxides, and residual forms. The experiment consisted of two horizons and two concentrations of metal, arranged in a randomized block design with three replications. After 17 hours of incubation, the samples were air dried, homogenized, passed through a 2 mm sieve and stored in plastic bags for subsequent extraction of the metals. The samples were subjected to the methodology of fractional extraction and the evaluation of the treatment with NaOH to characterize the oxides of Al was made. The fractional extraction showed to be adequate for studying the behavior of heavy metals in soil. The Cd was found mainly in the soluble and exchangeable forms and Cr in the more stable chemical forms (bound to Fe oxides and residual); Cu and Pb presented highest affinities towards Fe oxides and organic matter, respectively. Ni was found mainly in the residual form and showed lower affinity for organic matter. The study of Zn behavior was not possible, due to the contamination of extracts stored in flasks with rubber caps. There is still a need to improve a methodology to characterize metals associated with Fe and Al oxides.
fractional extraction; heavy metals; latosol; Fe and Al oxides