Belzile Nelson, Lang Chun-Yan, Chen Yu-Wei, Wang Mohui
Department of Chemistry and Biochemistry, Laurentian University, Sudbury, Ontario, Canada.
Sci Total Environ. 2008 Nov 1;405(1-3):226-38. doi: 10.1016/j.scitotenv.2008.06.034. Epub 2008 Jul 26.
The detailed distribution of mercury was studied in sediments and porewaters of two freshwater lakes, which were selected because of the contrasting conditions they present at their respective sediment-water interface (SWI). One lake is characterized by a SWI that remains oxic all year long whereas the other one shows a clear seasonal variation with the evolution of strongly anoxic conditions through the summer season. The results of the study clearly identify the importance of redox conditions on the geochemical behaviour of Hg at the SWI of both lakes but a very limited influence of an oxidized layer enriched in Fe and Mn oxyhydroxides at the top of the sediment of the oxic lake. In both lakes, a competitive effect on the cycling and mobility of the element was observed between natural organic matter and amorphous or organo-sulfide compounds. The proportion of Hg associated to natural organic matter in sediments showed a general increase with sediment depth. A fraction containing elemental Hg and Hg suspected to be bound to iron sulfides and organo-sulfides constituted the other major fraction of solid Hg in the sediments of both lakes. This second pool of Hg was generally larger at the top of the sediment where the production of dissolved sulfides is usually more detectable and it decreases with depth, suggesting that the metal is partially transferred from one pool being the sulfides including amorphous FeS and organo-sulfides to the organic matter pool. Methyl Hg represented less than 1% of the total Hg in sediments of both lakes. Our results obtained at different times of the summer season from two lakes contrasted by their SWI emphasize the competitive or alternating role played by dissolved and solid natural organic matter and sulfides on the fate of Hg in freshwater systems.
研究了两个淡水湖沉积物和孔隙水中汞的详细分布情况，选择这两个湖是因为它们在各自的沉积物 - 水界面（SWI）呈现出截然不同的条件。一个湖的特点是其沉积物 - 水界面全年保持有氧状态，而另一个湖则呈现出明显的季节性变化，夏季会出现强烈的缺氧状况。研究结果清楚地表明了氧化还原条件对两个湖泊沉积物 - 水界面汞地球化学行为的重要性，但对于有氧湖沉积物顶部富含铁和锰的羟基氧化物的氧化层影响非常有限。在两个湖泊中，均观察到天然有机物与无定形或有机硫化物化合物对元素循环和迁移的竞争作用。沉积物中与天然有机物结合的汞比例总体上随沉积物深度增加。包含元素汞以及疑似与硫化铁和有机硫化物结合的汞构成了两个湖泊沉积物中固体汞的另一主要部分。在沉积物顶部，这第二种汞库通常更大，因为那里溶解硫化物的产生通常更易检测到，且随深度降低，这表明该金属部分地从包括无定形硫化铁和有机硫化物在内的硫化物库转移到了有机物库。甲基汞在两个湖泊沉积物中的含量均不到总汞的1%。我们在夏季不同时间从两个因沉积物 - 水界面不同而形成对比的湖泊中获得的结果强调了溶解态和固态天然有机物以及硫化物在淡水系统中汞的归宿方面所起的竞争或交替作用。
