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首页> 美国卫生研究院文献>Geochemical Transactions >Speciation and fate of trace metals in estuarine sediments under reduced and oxidized conditions Seaplane Lagoon Alameda Naval Air Station (USA)
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Speciation and fate of trace metals in estuarine sediments under reduced and oxidized conditions Seaplane Lagoon Alameda Naval Air Station (USA)

机译：在还原和氧化条件下河口沉积物中微量金属的形态和结局水上飞机泻湖阿拉米达海军航空站（美国）

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We have identified important chemical reactions that control the fate of metal-contaminated estuarine sediments if they are left undisturbed (in situ) or if they are dredged. We combined information on the molecular bonding of metals in solids from X-ray absorption spectroscopy (XAS) with thermodynamic and kinetic driving forces obtained from dissolved metal concentrations to deduce the dominant reactions under reduced and oxidized conditions. We evaluated the in situ geochemistry of metals (cadmium, chromium, iron, lead, manganese and zinc) as a function of sediment depth (to 100 cm) from a 60 year record of contamination at the Alameda Naval Air Station, California. Results from XAS and thermodynamic modeling of porewaters show that cadmium and most of the zinc form stable sulfide phases, and that lead and chromium are associated with stable carbonate, phosphate, phyllosilicate, or oxide minerals. Therefore, there is minimal risk associated with the release of these trace metals from the deeper sediments contaminated prior to the Clean Water Act (1975) as long as reducing conditions are maintained. Increased concentrations of dissolved metals with depth were indicative of the formation of metal HS- complexes. The sediments also contain zinc, chromium, and manganese associated with detrital iron-rich phyllosilicates and/or oxides. These phases are recalcitrant at near-neutral pH and do not undergo reductive dissolution within the 60 year depositional history of sediments at this site.The fate of these metals during dredging was evaluated by comparing in situ geochemistry with that of sediments oxidized by seawater in laboratory experiments. Cadmium and zinc pose the greatest hazard from dredging because their sulfides were highly reactive in seawater. However, their dissolved concentrations under oxic conditions were limited eventually by sorption to or co-precipitation with an iron (oxy)hydroxide. About 50% of the reacted CdS and 80% of the reacted ZnS were bonded to an oxide-substrate at the end of the 90-day oxidation experiment. Lead and chromium pose a minimal hazard from dredging because they are bonded to relatively insoluble carbonate, phosphate, phyllosilicate, or oxide minerals that are stable in seawater. These results point out the specific chemical behavior of individual metals in estuarine sediments, and the need for direct confirmation of metal speciation in order to constrain predictive models that realistically assess the fate of metals in urban harbors and coastal sediments.
机译：我们已经确定了重要的化学反应，这些反应可以控制金属污染的河口沉积物（原位）或被疏dr时的命运。我们将来自X射线吸收光谱（XAS）的固体中金属分子键合的信息与从溶解的金属浓度获得的热力学和动力学驱动力相结合，以推断还原和氧化条件下的主要反应。我们根据加利福尼亚阿拉米达海军航空站60年的污染记录，评估了金属（镉，铬，铁，铅，锰和锌）的原位地球化学与沉积深度（至100厘米）的关系。 XAS的结果和孔隙水的热力学模型表明，镉和大多数锌形成稳定的硫化物相，铅和铬与稳定的碳酸盐，磷酸盐，页硅酸盐或氧化物矿物有关。因此，只要维持还原条件，与从《清洁水法》（1975年）之前受污染的较深沉积物中释放这些微量金属有关的风险最小。随着深度的增加，溶解金属的浓度增加表明金属HS -复合物的形成。沉积物中还含有锌，铬和锰，与碎屑富含铁的页硅酸盐和/或氧化物有关。这些相在接近中性pH的条件下是难分解的，并且在该位置沉积物的60年沉积历史内没有经历还原溶解。通过在原位地球化学与实验室中被海水氧化的沉积物进行比较，评估了这些金属在疏ging过程中的命运。实验。镉和锌是挖泥的最大危害，因为它们的硫化物在海水中具有很高的反应活性。然而，它们在有氧条件下的溶解浓度最终受到吸附（或与氢氧化铁（氧）共沉淀）的限制。在90天的氧化实验结束时，约50％的CdS反应物和80％的ZnS反应物被结合到氧化物衬底上。铅和铬的疏ging风险很小，因为它们与相对不溶的碳酸盐，磷酸盐，层状硅酸盐或在海水中稳定的氧化物矿物结合在一起。这些结果指出了河口沉积物中个别金属的特定化学行为，并且需要直接确认金属形态以限制预测模型，以实际评估城市港口和沿海沉积物中金属的命运。

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