Immobilization of As, Cr and Cu in CCA Contaminated soil using Laterite and Termitaria

Abstract

This study examined the effectiveness of laterite and termitaria (termite mound soil) to reduce subsurface metal mobility and availability to plant uptake in chromated-copper-aersenate (CCA) contaminated soil. The contaminated soil (MTotal = 447.16mg/kg; As = 6.84%, Cr = 58.43% and Cu = 34.73%) was treated with various amounts (0.5, 2, 4, 6, 8 and 10wt%) of the amendment soils in laboratory pot experiments. Sequential extraction procedure and plant uptake studies with maize seedlings were carried out and used to evaluate the solubility, mobility and transfer coefficients of the metals in the contaminated soil in relation to the levels of amendment application. It was found that the mobile fractions (water-soluble, exchangeable and carbonate bound) of As, Cr and Cu in the contaminated soil were transformed in the unavailable (Fe-Mn oxide bound, organic matter complexed and residual) forms following treatment with the amendment soils. The relative mobility factor (immobilization index), M_f/M_f^o was found to decrease with increase in the level of amendment application, was higher for termitaria than for laterite and was Cu < Cr < As. The observed difference in immobilization effectiveness was explained in terms of the difference in the binding capacity, resulting from the physico-chemical properties and surface chemistry, of the amendment soils. Heavy metal uptake by maize generally reflected the soluble/mobile pool and decreased with increase in the levels of amendment application.