Effects of the Addition of Phosphorus on the Redistribution of Cadmium, Copper, Lead, Nickel, and Zinc Among Soil Fractions in Contaminated Calcareous Soil

Abstract

A leaching experiment was conducted to examine the effects of phosphorus (monopotassium phosphate (MPP) and diammonium phosphate (DAP)) application on the redistribution of heavy metals (Cd, Cu, Pb, Ni, and Zn) among soil fractions in a contaminated calcareous soil. Columns were packed with contaminated soil and then leached using either 0.01 M (NH4)2HPO4, 0.01 M KH2PO4, or 0.01 M CaCl2 solutions until 15 pore volumes were collected. After leaching, the soil samples in the columns were sequentially extracted to obtain the exchangeable (EXCH), carbonate (CARB), organic matter (OM), magnesium oxide (MNO), iron oxide (FEO), and residual (RES) fractions. Application of MPP and DAP were found to alter the distribution of Cd, Cu, Pb, Ni, and Zn in the soil fractions. DAP significantly increased the concentrations of Cd, Cu, Ni and Zn in the EXCH fraction, whereas the Pb concentration decreased in response to the application of DAP and MPP. Moreover, leaching with MPP and DAP significantly increased the Cu and Zn concentrations in the CARB fraction, while the Pb concentrations decreased in these fractions. DAP and MPP effectively immobilized Pb, but the non-residual fraction of Cu and Zn increased in response to treatment with DAP and MPP. Finally, DAP increased the mobility of Cd, Cu, Ni and Zn in the soil, whereas the mobility index of Pb decreased in response to treatment with DAP and MPP. Taken together, these findings suggest that applying phosphate fertilizers may change over a long time the heavy metal fractions in contaminated calcareous soil, and that DAP may enhance Cd, Cu, Ni, and Zn mobility; therefore, the current phosphate fertilization management practices may need modification.