Abstract: The accumulation of heavy metals in soil could give impact to the environment, and the impact is related to the accumulated heavy metals’ bioavailability and mobility. This paper studied the feasibility of four methods, i.e., total analysis, sequential fractionation, chemical extraction, and column leaching, in evaluating the bioavailability and mobility, and the results showed that because of the difference in chemical forms of the metals in different soils, the total concentration of the metals in soil was not suitable to evaluate their bioavailability and mobility. Exchangeable forms of the metals obtained by chemical fractionation could better reflect, while the organic matter-bound forms of some metals had definite correlation with the bioavailability and mobility. There were no significant correlations between the oxides-bound and residual metals and the bioavailability and mobility. Column leaching was also feasible to evaluate the bioavailability and mobility. 0.01 mol·L^-1 CaCl₂ and 1 mol·L^-1 NH₄OAc extractable metals were significantly correlated with the metals concentrations in surface runoff and plant, and could better predict the potential runoff of heavy metals from soil and the accumulation of the metals in plants.

Key words: Organic acid, Cadmium, Microbial biomass, Red soil