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Role of bottom sediments in the secondary pollution of aquatic environments by heavy-metal compounds

机译：底部沉积物在重金属化合物对水环境的二次污染中的作用

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摘要

The results of long-term investigations into the concentrations of some heavy metals (Fe, Mn, Cu, Zn, Pb, Cr, and Cd) in the bottom sediments of the Dnieper reservoirs and the Dnieper–Bug estuary are considered. Maximum quantities of the metals studied are characteristic of southern water bodies located within industrial zones (the Zaporozh’e and Kakhovka reservoirs as well as the Dnieper–Bug estuary). The highest concentrations of the metals studied occurred in the clay silts (Fe, 11 600–32 400; Mn, 1504–3450; Cu, 38.9–85.5; Zn, 89.8–186.5; Cr, 48.6–193.0; and Cd, 1.9–4.4 mg kg-1 dry weight). Accumulation of heavy metals in the bottom sediments is an important factor in the self-purification of aquatic environments. However, this process is reversible and therefore provides a constant threat of secondary water pollution. Secondary water pollution is observed in summer and autumn when water consumption increases. The concentrations of heavy metals increase by a factor of 1.5–3 after the drawdown of the water level. The main reason for the rise in the concentrations of metals is exchange between the bottom sediments and the water column. The rate of heavy metal migration is connected with the forms of occurrence in solid substrates and pore solutions in the bottom sediments, as well as with physico-chemical conditions arising at the sediment/water boundary. Therefore, our investigations concentrated on the study of the fractional distribution of heavy metals among solid substrates and their forms of occurrence in interstitial solutions. This distribution depends, most of all, on the chemical properties of metals as well as the chemical and mineralogical composition of the sediments and the chemical properties of pore solutions. Most of the supply of Mn, Zn, Fe, and Cd is associated with oxides and hydroxides of iron and manganese (Mn, 74–93%; Zn, 43–70%; Fe, 27–59%; and Cd, 28–41%). Most copper and chromium is bound to organic matter and to scarcely soluble minerals. In the interstitial solutions studied, metals (except manganese) are found mainly as complex compounds with dissolved organic matter of a different molecular weight. Nevertheless, the fraction of complexes with a relatively low molecular weight (500–5000 Da) prevailed (40–70%). Dissolved manganese in the pore solutions consists chiefly of free (hydrated) ions Mn2+ (80–95%). The results obtained were used for a comparative evaluation of heavy metal mobility and the exchange ability of their associated compounds in the bottom sediment–water system.
机译：考虑对第聂伯河水库和第聂伯河-布格河口底部沉积物中某些重金属（Fe，Mn，Cu，Zn，Pb，Cr和Cd）的浓度进行长期调查的结果。所研究金属的最大量是位于工业区（Zaporozh'e和Kakhovka水库以及第聂伯河-布格河口）内的南部水体的特征。所研究的金属的最高浓度发生在粘土粉砂中（Fe，11 600–32 400； Mn，1504–3450； Cu，38.9–85.5； Zn，89.8–186.5； Cr，48.6–193.0； Cd，1.9–3）。 4.4 mg kg-1干重）。底部沉积物中重金属的积累是水生环境自我净化的重要因素。但是，该过程是可逆的，因此不断带来二次水污染的威胁。当用水量增加时，在夏季和秋季观察到二次水污染。水位下降后，重金属的浓度增加了1.5–3。金属浓度升高的主要原因是底部沉积物与水柱之间的交换。重金属迁移的速度与固体沉积物和底部沉积物中孔隙溶液的发生形式以及沉积物/水边界处发生的物理化学条件有关。因此，我们的研究集中在固体基质中重金属的分数分布及其在间隙溶液中的发生形式的研究。这种分布主要取决于金属的化学性质，沉积物的化学和矿物组成以及孔隙溶液的化学性质。锰，锌，铁和镉的大部分供应与铁和锰的氧化物和氢氧化物有关（锰，74-93％；锌，43-70％；铁，27-59％；镉，28- 41％）。大多数铜和铬与有机物和难溶的矿物结合。在研究的间隙溶液中，主要发现金属（锰除外）为具有不同分子量溶解有机物的复杂化合物。尽管如此，分子量相对较低（500-5000 Da）的复合物占主导地位（40-70％）。孔隙溶液中溶解的锰主要由游离（水合）离子Mn2 +（80-95％）组成。所获得的结果用于比较评估底部沉积物-水系统中的重金属迁移率及其相关化合物的交换能力。

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