Peretyazhko T, Charlet L, Muresan B, Kazimirov V, Cossa D
Observatory of Earth and Planetary Sciences (OSUG), University of Grenoble-1, F.38041 Grenoble, France.
Sci Total Environ. 2006 Jul 1;364(1-3):260-71. doi: 10.1016/j.scitotenv.2005.06.016. Epub 2005 Aug 2.
Formation of dissolved gaseous mercury (DGM) and its volatilization from aquatic systems can be considered as a natural attenuation process, which limits the methylation of mercury (Hg) and Hg accumulation in fish. Although gold-mining activity and erosion of tropical soils lead to increased Hg concentration in aquatic systems, little is known about DGM production and distribution in tropical aqueous systems. Our work explores the vertical distribution and principal sources of DGM in a meromictic Amazonian reservoir. Dissolved gaseous mercury measurements carried out in Petit-Saut reservoir (French Guiana, South America) revealed DGM increase in the surface waters and at the bottom layers of the reservoir during the dry season. As in arctic and temperate lakes, high DGM concentrations in surface waters were attributed to sunlight-mediated photochemical processes. Dissolved gaseous mercury concentrations in the anaerobic hypolimnion were larger than in temperate or arctic lakes. In order to elucidate Hg(II) reduction pathways in the bottom layer of tropical reservoir, laboratory Hg(II) reduction experiments were performed with anoxic aqueous suspensions of surface sediments either untreated or treated by gamma-ray and NaN3. Our results indicated that DGM production at the bottom layer of Petit-Saut reservoir was biologically mediated. Dissolved gaseous mercury formation rates in the surface sediment suspensions were of the same order of magnitude as formation rates in freshwater lakes reported in literature.
溶解态气态汞（DGM）的形成及其从水生系统中的挥发可被视为一种自然衰减过程，该过程限制了汞（Hg）的甲基化以及鱼类体内汞的积累。尽管金矿开采活动和热带土壤侵蚀导致水生系统中汞浓度升高，但对于热带水域系统中DGM的产生和分布却知之甚少。我们的研究探索了亚马逊河半咸水湖水库中DGM的垂直分布及其主要来源。在南美洲法属圭亚那的佩蒂 - 索特水库进行的溶解态气态汞测量显示，在旱季，水库表层水和底层水中的DGM含量增加。与北极和温带湖泊一样，表层水中高浓度的DGM归因于阳光介导的光化学过程。厌氧温跃层中的溶解态气态汞浓度高于温带或北极湖泊。为了阐明热带水库底层汞（II）的还原途径，我们用未经处理或经伽马射线和叠氮化钠处理的表层沉积物缺氧水悬浮液进行了实验室汞（II）还原实验。我们的结果表明，佩蒂 - 索特水库底层DGM的产生是由生物介导的。表层沉积物悬浮液中溶解态气态汞的形成速率与文献报道的淡水湖泊中的形成速率处于同一数量级。
