Immobilization of heavy metals in rhizosphere soils : formulation of phytostabilization technology

为了在靶场土壤中制定成功的植物稳定策略，了解重金属在根际土壤中如何在分子水平上被固定是至关重要的。本研究的目的是探讨不同植物根际土壤中铅形态的变化，以及铅颗粒在根际土壤中的溶解性及其对土壤生态系统的影响。采用扩展X射线吸收精细结构(EXAFS)光谱和化学萃取法研究了5种不同植物根际土壤中铅的形态和溶解性。EXAFS分析表明，土壤中铅以PbCO3的形式存在，铅吸附在有机质上，铅吸附在土生水钠石和/或水合铁上。EXAFS光谱分析表明，土壤的细微结构存在显著差异，说明根际过程对土壤中的铅形态有一定的修饰作用。变性梯度凝胶电泳法显示，植物在污染土壤中的生长似乎丰富了细菌种群，因为根际土壤的总带型比对照土壤亮。PH值为~7时，土壤中细菌多样性增强。

To formulate successful phytostabilization strategies in a shooting range soil, understanding how heavy metals are immobilized at the molecular level in the rhizosphere soil is critical. The objectives of this study were to investigate i) how Pb speciation was modified in the rhizosphere soils of various plant species, and ii) solubility of Pb pellet in rhizosphere and subsequent impacts on soil ecosystems. Lead (Pb) speciation and solubility in rhizosphere soils of five different plant species were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy and chemical extraction. The EXAFS analysis indicated that Pb occurred as PbCO_3, Pb sorbed to organic matter, and Pb sorbed to pedogenic birnessite and/or ferrihydrite in the bulk soil. Comparison of the EXAFS spectra between bulk and rhizosphere soils demonstrated notable differences in fine structure, indicating that Pb species had been modified by rhizosphere processes. Denatured gradient gel electrophoresis demonstrated that Plant growth in the contaminated soil appeared to enrich bacterial populations since the general band profile exhibited in the rhizosphere soil was brighter than the control soil. Bacterial diversity was enhanced in the soil with the pH value of～7.