Sarret Géraldine, Balesdent Jérome, Bouziri Lamia, Garnier Jean-Marie, Marcus Matthew A, Geoffroy Nicolas, Panfili Frédéric, Manceau Alain
Environmental Geochemistry Group, LGIT, University of Grenoble and CNRS, BP 53, 38041 Grenoble, Cedex 9, France.
Environ Sci Technol. 2004 May 15;38(10):2792-801. doi: 10.1021/es035171t.
Soils that have been acutely contaminated by heavy metals show distinct characteristics, such as colonization by metal-tolerant plant species and topsoil enrichment in weakly degraded plant debris, because biodegradation processes are strongly inhibited by contamination. Such an organic topsoil, located downwind of an active zinc smelter and extremely rich in Zn (approximately 2%, dry weight), was investigated by X-ray diffraction, synchrotron-based X-ray microfluorescence, and powder- and micro-extended X-ray absorption fine structure (EXAFS) spectroscopy for Zn speciation and by isotopic dilution for Zn lability. EXAFS spectra recorded on size fractions and on selected spots of thin sections were analyzed by principal component analysis and linear combination fits. Although Zn primary minerals (franklinite, sphalerite, and willemite) are still present (approximately 15% of total Zn) in the bulk soil, Zn was found to be predominantly speciated as Zn-organic matter complexes (approximately 45%), outer-sphere complexes (approximately 20%), Zn-sorbed phosphate (approximately 10%), and Zn-sorbed iron oxyhydroxides (approximately 10%). The bioaccumulated Zn fraction is likely complexed to soil organic matter after the plants' death. The proportion of labile Zn ranges from 54 to 92%, depending on the soil fraction, in agreement with the high proportion of organically bound Zn. Despite its marked lability, Zn seems to be retained in the topsoil thanks to the huge content of organic matter, which confers to this horizon a high sorption capacity. The speciation of Zn in this organic soil horizon is compared with that found in other types of soils.
被重金属严重污染的土壤呈现出明显的特征，比如耐金属植物物种的定殖以及弱降解植物残体在表层土壤中的富集，因为生物降解过程受到污染的强烈抑制。对位于一座活跃锌冶炼厂下风向、锌含量极高（约2%，干重）的这种有机表层土壤，采用X射线衍射、基于同步加速器的X射线微荧光以及粉末和微扩展X射线吸收精细结构（EXAFS）光谱法研究锌的形态，并采用同位素稀释法研究锌的活性。通过主成分分析和线性组合拟合分析了在不同粒径级分和薄片选定斑点上记录的EXAFS光谱。尽管在土壤总体中锌的原生矿物（锌铁尖晶石、闪锌矿和硅锌矿）仍然存在（约占总锌的15%），但发现锌主要以锌-有机物络合物（约45%）、外层络合物（约20%）、吸附锌的磷酸盐（约10%）和吸附锌的羟基氧化铁（约10%）的形态存在。植物死亡后，生物累积的锌部分可能与土壤有机质络合。根据土壤粒径级分不同，活性锌的比例在54%至92%之间，这与有机结合锌的高比例相一致。尽管锌具有明显的活性，但由于有机质含量巨大，锌似乎保留在表层土壤中，这赋予了该土层较高的吸附能力。将该有机土壤层中锌的形态与其他类型土壤中的情况进行了比较。
