Geochemical Switches

生物硫化物深刻地影响着许多元素的地球化学行为。本研究的重点是HS-与Mo， Re, Ge， As和Sb元素的氧阴离子之间的相互作用。在某些情况下，在HS-存在的情况下，核心元素周围的S原子取代O原子形成可溶性硫阴离子。核心元素的地球化学性质发生了戏剧性的变化。研究最好的例子是MoO42-向MoS42-的转变，在H2S(aq) = 11 3 ？接近平衡条件下的M。转变的突兀特征以及硫阴离子与氧阴离子在地球化学性质上的显著差异使我们将这种转变描述为地球化学开关（Helz et al. 1996）。硫化物驱动开关影响核心元素的重要地球化学性质：迁移率、生物利用度以及与其他溶质的化学相互作用。由于硫阴离子是多齿的、供硫的配体，它们与软金属（包括许多有害金属）的相互作用特别强烈。这种相互作用的环境和生物地球化学影响仍然未知。校准开关的动作点将增强微量元素作为古氧化还原指标的使用。主要目标是生产地球化学模型所需的各种基础数据，以预测还原环境中元素的行为。

Helz9980532Biogenic sulfide profoundly affects geochemical behavior of many elements. This study focuses on interactions between HS- and oxyanions of the elements Mo, Re, Ge, As and Sb. In some cases soluble thioanions are formed by replacement of O atoms by S atoms around the core element in the presence of HS-. A dramatic switch in the geochemical properties of the core element ensues. The best studied example, the transformation of MoO42- to MoS42-, occurs abruptly at H2S(aq) = 11 3 ?M under near-equilibrium conditions. The abrupt character of the transformation and marked difference in geochemical properties of the thioanion vs. the oxyanion have led us to describe this transformation as a geochemical switch (Helz et al. 1996). Sulfide-actuated switches affect important geochemical properties of core elements: mobility, bioavailability, and chemical interactions with other solutes. Because thioanions are multidentate, sulfur-donating ligands, they are expected to interact particularly strongly with soft metals, which include many hazardous metals. The environmental and biogeochemical implications of such interactions are still unknown. Calibrating the action points of switches will enhance the use of trace elements as paleoredox indicators. The chief goal is production of the kinds of fundamental data needed in geochemical models to predict behavior of elements in reducing environments.