Mobility and Speciation of Lead in Shooting Range Soils Treated with Chemically-Assisted Phytostabilization Using X-ray Absorption Spectroscopy (XAS).

A shooting range soil contaminated with Pb was used to examine native plant and byproduct amendment application for immobilization efficacy of metal. The focus of this study was to evaluate the effectiveness of phytostabilization applied in conjunction with an immobilizing amendment (incinerated poultry waste) on attenuation of Pb mobility and restoration of chemical properties of Pb contaminated shooting range soils. A large column study was performed to assess the attenuation of downward Pb dissolution and modification of Pb speciation in solid and liquid phases for four treatments: Control, plant application, amendment application (incinerated poultry waste), and plant and amendment applications. The amendment reduced water-extractable Pb by about 43% of the Control. A column study revealed that cumulative leachate Pb over 100 days was increased by the sole application of amendment (0.32 mg) compared to the Control (0.27 mg), but was reduced to 0.23 mg by the combined use of plant and amendment. Thermodynamic equilibrium calculations demonstrated that predicted Pb2+ activity was saturated with respect to cerussite in Control and was supersaturated with respect to chloropyromorphite in the amended soils. The EXAFS analysis revealed that the amendment reduced the proportion of cerussite and altered it to a more geochemically stable species of chloropyromorphite that occupied 38% of the total Pb species. Our results suggest that the use of plant in combination with incinerated poultry waste as a Pb immobilizing amendment attenuated downward Pb leaching and altered Pb species to more geochemically stable phases.