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TECHNICAL REPORTS

Heavy Metals in the Environment

Impacts of Chemical Amendment and Plant Growth on Lead Speciation and Enzyme Activities in a Shooting Range Soil: An X-ray Absorption Fine Structure Investigation

^a Dep. of Bioresource Science, Mie University, 1577 Kurimamachiya, Tsu 514-8507 Japan
^b Dep. of Civil Engineering, Gifu Univ., 1-1 Yanagido, Gifu 501-1193 Japan
^c Gifu Prefectural Institute for Bioengineering, 3481-2 Hachiya, Minokamo, Gifu 505-0004 Japan
^d Dep. of Urban and Environmental Engineering, Graduate School of Engineering, Kyoto Univ., C-1-3, Nishikyo-ku, Kyoto 615-8540 Japan
^e Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Mikazuki, Sayo, Hyogo 679-5198 Japan

^* Corresponding author (yhashim{at}bio.mie-u.ac.jp).

Received for publication September 25, 2008. In situ chemical immobilization is a practical remediation technology for metal-contaminated soils because of its capability to reduce cost and environmental impacts. We assessed the immobilization effects of poultry waste amendment and plant growth (Panicum maximum Jacq.) on Pb speciation and enzyme activities in shooting range soils. Soil contaminated with Pb was obtained from the top 20 cm of a shooting range. To evaluate Pb mobility in the soil profile treated with plants and immobilizing amendment, we used large columns filled with Pb-contaminated soil (0–20 cm, surface soils) and non-contaminated soil (20–75 cm, subsurface soils). The column study demonstrated that the amendment reduced the toxicity characteristic leaching procedure–extractable Pb in the surface soil by 90% of the Control soil. Lead mobility from the surface to subsurface profiles was significantly attenuated by plant growth but was promoted by the amendment without plant application. The extended X-ray absorption fine structure analysis revealed that the amendment reduced the proportion of PbCO₃ and Pb-organic complexes and transformed them into a more geochemically stable species of Pb₅(PO₄)₃Cl with 30 to 35% of the total Pb species. Applications of plant and amendment increased activities of dehydrogenase and phosphatase in the surface soil with 2.7- and 1.1-fold greater than those in Control, respectively. The use of amendments in combination with plant growth may have potential as an integrated remediation strategy that enables Pb immobilization and soil biological restoration in shooting range soils.

Abbreviations: CN, coordination numbers • EXAFS, extended X-ray absorption fine structure • LCF, linear combination fitting • RSF, radial structure functions • SI, saturation index • SOM, soil organic matter