The Fate of As and Heavy Metals in the Flooded Paddy Soil Stabilized by Limestone and Steelmaking Slag

The characteristics of As and heavy metals depend on the oxidation/reduction condition of the soil environment. The mostheavy metals are immobilized by the reduction condition whereas As, Fe and Mn become more soluble. Therefore thisstudy estimated the stabilization efficiency of the agricultural paddy soil in the vicinity of the abandoned mine using aflooded column test including analysis of the soil solution, contaminants fractionation and rice grain. Limestone andsteelmaking slag were used as amendments for stabilization of the contaminated soil. In an analysis of the soil solution, themobile characteristics of Fe and Mn, which were used as electron acceptors of the microorganisms, were controlled byincreasing the pH by adding alkali amendments. This means that the contaminants combined with Fe and Mn can be stableunder flooded reduction condition. However, the concentrations of cationic heavy metals (Cd, Pb, and Zn) were alsodecreased without amendments because the carbonates produced from microbial respiration increased the pH of the soilsolution. In the amended soil, the specific sorbed fraction of As and carbonates fraction of heavy metals were increasedwhen compared to the control soil at the end of the column test. Especially in heavy metals, the increase of carbonatesfraction seems to be influenced by alkali amendments rather than microbial respiration. Because of the stabilization effect inthe flooded paddy soil, the contents of As and Zn in rice grain from amended soil were lower than that of the control soil.But additional research is needed because of the relatively higher Pb content identified in the rice grain from the amended.Key words :As, Heavy metal, Stabilization, Paddy, Rice grain