Groupement de Recherche Eau Sol Environnement, Université de Limoges, 123 avenue Albert Thomas, 87060 Limoges Cedex, France.
Université de Lyon, UMR5023 Laboratoire d'Ecologie des Hydrosystèmes Naturels et Anthropisés, Université Lyon 1, ENTPE, CNRS, 3, rue Maurice Audin, 69518 Vaulx-en-Velin, France.
Sci Total Environ. 2017 Dec 15;605-606:666-676. doi: 10.1016/j.scitotenv.2017.06.236. Epub 2017 Jul 1.
In a hydroelectric reservoir, sediments are subject to remobilization events, water-level fluctuations and physicochemical changes. Depending on their associated metallic content, surficial oxic to suboxic sediments could constitute a major source of metals. To identify the key parameters that control metallic elements in terms of their mobility and sensitivity to reservoir management, sediments were subject to resuspension and drying/wetting cycle experiments over a wide range of pH values, solid/liquid ratios (S/L) and redox (Eh) conditions. During these tests, special attention was also paid to the influence of pretreatments on samples, i.e., drying, aeration and the leachate composition (ultrapure water vs. natural water); on the preservation of the sediment characteristics; and especially on metallic element release. The results of this study show that the pH, S/L ratio and Eh parameters are key variables in metal solubilization; the pH influences metal mobility primarily through sorption-desorption phenomena as well as the dissolution of metallic-bearing phases, the S/L ratio modifies the sorption-desorption equilibria, and the Eh primarily affects the reducible sensitive phases and associated metallic elements through dissolution-precipitation processes. Under environmental conditions, evolution of these parameters can lead to a >20% solubilization of the most mobile elements, i.e., As and Cd. These results are influenced by the sample pretreatment and experimental conditions. In fact, even if the solubilization patterns show no significant differences between dry and wet sediment depending on the physicochemical conditions, the magnitude of their release is significantly affected. Drying pretreatment induces changes in metal speciation, notably altering the distribution of the most weakly bound elements; there is almost half the amount of metallic elements associated with the exchangeable fraction in dry compared to wet sediments. The solubilization percentages were higher in the ultrapure phase than in reservoir water primarily due to the low pH, which influenced the sorption equilibria.
在水力发电水库中，沉积物会经历再悬浮事件、水位波动和物理化学变化。根据其相关的金属含量，表层好氧至亚缺氧沉积物可能是金属的主要来源。为了确定控制金属元素迁移性和对水库管理敏感性的关键参数，对沉积物进行了广泛的 pH 值、固液比（S/L）和氧化还原（Eh）条件下的再悬浮和干湿循环实验。在这些测试中，还特别注意了预处理对样品的影响，例如干燥、曝气和浸出液成分（超纯水与天然水）；对沉积物特征的保存；特别是对金属元素释放的影响。研究结果表明，pH、S/L 比和 Eh 参数是金属溶解的关键变量；pH 通过吸附-解吸现象以及含金属相的溶解对金属迁移性产生主要影响，S/L 比改变吸附-解吸平衡，Eh 通过溶解-沉淀过程主要影响可还原敏感相和相关金属元素。在环境条件下，这些参数的演变可能导致最易迁移的元素（如 As 和 Cd）的溶解率超过 20%。这些结果受到样品预处理和实验条件的影响。实际上，即使在物理化学条件下，干燥和湿沉积物之间的溶解模式没有显著差异，但它们的释放程度受到显著影响。干燥预处理会改变金属形态，特别是改变最不牢固结合元素的分布；与湿沉积物相比，干燥沉积物中与可交换部分相关的金属元素数量几乎减少了一半。与水库水相比，超纯相中金属元素的溶解百分比更高，主要是因为低 pH 值影响了吸附平衡。
