The distribution and elevated solubility of lead, arsenic and cesium in contaminated paddy soil enhanced with the electrokinetic field

Abstract

The objectives of this study were to investigate fractionation, solubility and potential bioavailability of Pb, As and Cs in Mississippi River Delta paddy soil under an electrokinetic field (EKF). Effects of EKF on soil pH changes and solid-phase distributions of metal(loid)s were examined. Results showed that fractionation of Pb, As and Cs was largely determined by the nature of elements, loading levels and EKF treatment. Native Pb in the soil was mostly in the amorphous iron oxide, organic matter and residual fractions, native As in the amorphous iron oxide, easily reducible oxide and residue fractions while native Cs in the residue fraction. Added Pb, As and Cs showed distinguished solid-phase distributions: Pb dominantly in the organic matter fraction; As in the amorphous iron oxide fraction, and Cs in the residue with a significant water-soluble plus exchangeable fraction. EKF treatment is effective on lowering soil pH to 1.5 near the anode due to water electrolysis releasing proton which is beneficial for dissolution of metal(loid)s, increasing their overall solubility. The acidification in the anode soil efficiently increased the water-soluble Pb and the exchangeable Cs, implying enhanced solubility and elevated their overall potential bioavailability in the anode region while lower solubility in the cathode area. The building up of water-soluble As in the anode region may be from electromigration of As anion from the cathode. This study shows significant enhancement of redistribution, elevated solubility and overall bioavailability of Pb, As and Cs in Mississippi Delta paddy soil under the EKF.