Brown G E, Foster A L, Ostergren J D
Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, USA.
Proc Natl Acad Sci U S A. 1999 Mar 30;96(7):3388-95. doi: 10.1073/pnas.96.7.3388.
There is a continual influx of heavy metal contaminants and pollutants into the biosphere from both natural and anthropogenic sources. A complex variety of abiotic and biotic processes affects their speciation and distribution, including adsorption onto and desorption from mineral surfaces, incorporation in precipitates or coprecipitates, release through the dissolution of minerals, and interactions with plants and microbes. Some of these processes can effectively isolate heavy metals from the biosphere, whereas others cause their release or transformation to different species that may be more (or less) bioavailable and/or toxic to organisms. Here we focus on abiotic adsorption and precipitation or coprecipitation processes involving the common heavy metal contaminant lead and the metalloids arsenic and selenium in mine tailings and contaminated soils. We have used extremely intense x-rays from synchrotron sources and a structure-sensitive method known as x-ray absorption fine structure (XAFS) spectroscopy to determine the molecular-level speciation of these elements at concentrations of 50 to several thousand ppm in the contaminated environmental samples as well as in synthetic sorption samples. Our XAFS studies of As and Pb in the mine tailings show that up to 50% of these contaminants in the samples studied may be present as adsorbed species on mineral surfaces, which makes them potentially more bioavailable than when present in sparingly soluble solid phases. Our XAFS studies of Se(VI) sorption on Fe2+-containing sulfates show that this element undergoes redox reactions that transform it into less bioavailable and less toxic species. This type of information on molecular-level speciation of heavy metal and metalloid contaminants in various environmental settings is needed to prioritize remediation efforts and to assess their potential hazard to humans and other organisms.
重金属污染物和其他污染物通过自然和人为来源持续不断地流入生物圈。各种各样复杂的非生物和生物过程影响着它们的形态和分布，包括在矿物表面的吸附和解吸、在沉淀物或共沉淀物中的结合、通过矿物溶解的释放以及与植物和微生物的相互作用。其中一些过程可以有效地将重金属与生物圈隔离开来，而其他过程则导致它们释放或转化为对生物可能更具（或更少）生物可利用性和/或毒性的不同物种。在这里，我们重点关注涉及矿山尾矿和受污染土壤中常见重金属污染物铅以及类金属砷和硒的非生物吸附和沉淀或共沉淀过程。我们使用了来自同步加速器源的极强X射线以及一种称为X射线吸收精细结构（XAFS）光谱的结构敏感方法，来确定这些元素在受污染环境样品以及合成吸附样品中浓度为50至数千ppm时的分子水平形态。我们对矿山尾矿中砷和铅的XAFS研究表明，在所研究的样品中，高达50%的这些污染物可能以吸附物种的形式存在于矿物表面，这使得它们可能比以微溶固相形式存在时更具生物可利用性。我们对含Fe2 + 的硫酸盐上硒（VI）吸附的XAFS研究表明，该元素会发生氧化还原反应，将其转化为生物可利用性和毒性较低的物种。需要这类关于各种环境中重金属和类金属污染物分子水平形态的信息，以确定修复工作的优先级并评估它们对人类和其他生物的潜在危害。
