Evaluation of Pb remediated soils by means of different availability indices

Abstract

Lead immobilization was examined on a Pb contaminated soil(1500 mg Pb kg-1) using 7 different soil treatments: bentonite, zeolites, cyclonic ashes, compost, lime, steelshots and hydroxyapatite. The immobilizing effect of the soil additives by 3 availability indices: the modified distribution coefficient (Kmd), bioavailability factor (BF) and the transfer factor(TF). The Kmd is defined as the ratio of Pb in soil to its concentration in the soil solution. The BF is defined as the ratio of Pb in soil to its concentration in the soil solution. The BF is defined as the ratio of Pb content in the exchangeable phase to the total Pb concentration in soil. The TF is defined as the ratio of the Pb content in plant tissue(lettuce) to the total concentration of Pb in soil Kmd and BF correlated well with the capacity of some enzymes in test plants known to react under (metal induced) oxidative stress. Application of zeolite was problematic due to soil compaction while steelshots released toxic amounts of Fe and Mn which killed lettuce seedings. Cyclonic ashes, compost, hydroxyapatite and lime substantially increased Kmd and decreased BF and TF.