Competitive adsorption and mobility sequence of heavy metals in urban soils of southeastern China

Heavy metals can be introduced into urban soils at the same time. Ther efore, their selective retention and competitive adsorption by the soils become of major importance in determining their availability and movement throughout th e soil. In this study, the availability and mobility of six heavy metals in eigh t urban soils collected from different cities of Zhejiang Province, southeastern China were assessed using distribution coefficients(Kd) and retardation factor( Rf). The results showed that there were great differences in the Kd and Rf among the tested soils. The adsorption sequences were Cr>Pb>Cu>Cd>Zn>Ni, and the Kd d ecreased with increasing levels of metal addition. Ni generally has the lowest R f values followed closely by Cd, and Zn whereas Cr and Pb reached the highest v alues. The results suggest that Ni and Zn have the highest mobility associated t o the lowest adsorption, Cr and Pb present the opposite behavior. Correlation an alysis indicates that soil pH, CaCO3 content, and cation exchange capacity(CEC) are key factors controlling the solubility and mobility of the metals in the urb an soils.