Attenuation of lead leachability in shooting range soils using poultry waste amendments in combination with indigenous plant species

Chemical immobilization technology utilizing poultry waste (PW) along with a native plant (Panicum maximum Jacq.) application was assessed for the attenuation of downward Pb dissolution and modification of Pb speciation in solid and liquid phases in the soil. A large column study with and without plant and PW applications was conducted using a Pb contaminated soil collected from a shooting range area. The PW application reduced water-extractable Pb by about 43% of that of the treatment without the PW and plant applications (Control). The cumulative Pb amount in column leachates over 100 d was increased by the PW amendment (0.32 mg) compared to Control (0.27 mg), but was reduced to 0.23 mg by the combined use of plant and PW amendment. Sequential extraction analysis revealed that the Pb fractions of PW-amended soils were shifted to less soluble phases as indicated by an increased residual fraction (20%) and decreased exchangeable and carbonate fractions (22%) than those in the Control soil. Thermodynamic equilibrium calculations demonstrated that predicted Pb2+ activity was saturated with respect to cerussite in the Control soil and was supersaturated with respect to chloropyromorphite in the PW-amended soils. Our results suggest that the use of plant in combination with PW as a Pb immobilizing amendment attenuated downward Pb leaching and altered Pb species to more geochemically stable phases.