Fractionation of Heavy Metals in Soils as Affected by Soil Types and Metal Load Quantity

Two series of soil subsamples, by spiking copper(Cu),lead(Pb),zinc(Zn)and cadmium(Cd)in an orthogonal design,were prepared using red soil and brown soil,respectively.The results indicated that heavy metal fractions in these soil subsamples depended not only on soil types,but also on metal loading quantity as well as on interactions among metals in soil.Lead and Cu in red soil appeared mostly in weakly specifically adsorbed(WSA),Fe and Mn oxides bound(OX),and residual(RES)fractions.Zine cxisted in all fractions except organic bound one,and Cd was major in water soluble plus exchangeable(SE)one.Different from the results of red soil,Pb and Cu was present in brown soil in all fractions except organic one,but over 75% of Zn and 90% of Cd existed only in SE fraction.Meanwhile,SE fraction for any metal in red soil was lower than that in brown soil and WSA and OX fractions were higher.It is in agreernent with low cation exchange capacity and large amounts of metal oxides included in red soil.Metal fractions in soil,especially for water soluble plus exchangeable one ,were obviously influenced by other coexisting metals.The SE fraction of heavy metals increased with increasing loading amounts of metals in red soil but not obviously in brown soil,which suggest that metal availability be easily affected by their total amounts spiked in red soil.In addition,more metals in red soil were extracted with 0.20 mol L^-1 NH4Cl（pH5.40）than that with 1.0 mol L^-1 Mg(NO3)2(pH7.0),but the reverse happened in brown soil,implicating significantly different mechanisms of metal desorption from red soil and brown soil.

Two series of soil subsamples, by spiking copper (Cu), lead (Pb), zinc (Zn) and cadmium (Cd) in an orthogonal design, were prepared using red soil and brown soil, respectively. The results indicated that heavy metal fractions in these soil subsamples depended not only on soil types, but also on metal loading quantity as well as on interactions among metals in soil. Lead and Cu in red soil appeared mostly in weakly specifically adsorbed (WSA), Fe and Mn oxides bound (OX), and residual (RES) fractions. Zinc existed in all fractions except organic bound one, and Cd was major in water soluble plus exchangeable (SE) one. Different from the results of red soil, Pb and Cu was present in brown soil in all fractions except organic one, but over 75% of Zn and 90% of Cd existed only in SE fraction. Meanwhile, SE fraction for any metal in red soil was lower than that in brown soil and WSA and OX fractions were higher. It is in agreement with low cation exchange capacity and large amounts of metal oxides included in red soil. Metal fractions in soil, especially for water soluble plus exchangeable one, were obviously influenced by other coexisting metals. The SE fraction of heavy metals increased with increasing loading amounts of metals in red soil but not obviously in brown soil, which suggest that metal availability be easily affected by their total amounts spiked in red soil. In addition, more metals in red soil were extracted with 0.20 mol L-1 NH4Cl (pH 5.40) than that with 1.0 mol L-1 Mg(NO3)2 (pH 7.0), but the reverse happened in brown soil, implicating significantly different mechanisms of metal desorption from red soil and brown soil.