Department of Chemistry, Eastern Kentucky University, Richmond, KY 40475, USA.
Department of Chemistry and Biochemistry, University of Mississippi, University, MS 38677, USA.
Molecules. 2022 Aug 1;27(15):4911. doi: 10.3390/molecules27154911.
Wetlands are of a considerable environmental value as they provide food and habitat for plants and animals. Several important chemical transformations take place in wetland media, including the conversion of inorganic mercury (Hg) to monomethylmercury (MeHg), a toxic compound with a strong tendency for bioconcentration. Considering the fact that wetlands are hotspots for Hg methylation, we investigated, for the first time, Hg methylation and demethylation rates in an old growth cypress wetland at Sky Lake in the Mississippi Delta. The Sky Lake ecosystem undergoes large-scale water level fluctuations causing alternating periods of oxic and anoxic conditions in the sediment. These oscillating redox conditions, in turn, can influence the transformation, speciation, and bioavailability of Hg. In the present study, sediment cores from the wetland and Sky Lake itself were spiked with enriched stable isotope tracers of inorganic Hg and MeHg and allowed to incubate (in-situ) before freezing, sectioning, and analysis. Methylation rates (day−1) ranged from 0.012 ± 0.003 to 0.054 ± 0.019, with the lowest rate in the winter and the highest in the summer. Demethylation rates were about two orders of magnitude higher, and also greater in the warmer seasons (e.g., 1.84 ± 0.78 and 4.63 ± 0.51 for wetland sediment in the winter and summer, respectively). Methylation rates were generally higher in the open water sediment compared to wetland sediment, with the latter shaded and cooler. Both methylation (r = 0.76, p = 0.034) and demethylation (0.97, p = 0.016) rates (day−1) were positively correlated with temperature, but not with most other water quality parameters. MeHg concentration in the water was correlated with pH (r = 0.80, p < 0.05), but methylation rates were only marginally correlated (r = 0.71). Environmental factors driving microbial production of MeHg in the system include warm temperatures, high levels of labile natural organic matter, and to a lesser extent the relatively low pH and the residence time of the water. This study also provides baseline data that can be used to quantify the impacts of modifying the natural flow of water to the system on Hg methylation and demethylation rates.
湿地具有相当大的环境价值，因为它们为植物和动物提供了食物和栖息地。湿地介质中会发生几种重要的化学转化，包括无机汞（Hg）向一甲基汞（MeHg）的转化，后者是一种具有强烈生物浓缩倾向的有毒化合物。考虑到湿地是汞甲基化的热点，我们首次调查了密西西比三角洲天空湖古老柏木湿地的汞甲基化和去甲基化速率。天空湖生态系统经历大规模的水位波动，导致沉积物中的好氧和缺氧条件交替出现。这些振荡的氧化还原条件反过来又会影响汞的转化、形态和生物利用度。在本研究中，从湿地和天空湖本身采集了沉积物岩芯，并用富含无机汞和一甲基汞的稳定同位素示踪剂进行了接种，并在冷冻、切片和分析之前进行了原位孵育。甲基化速率（天-1）范围为 0.012±0.003 至 0.054±0.019，冬季最低，夏季最高。去甲基化速率约高两个数量级，在温暖季节更高（例如，冬季和夏季湿地沉积物分别为 1.84±0.78 和 4.63±0.51）。与湿地沉积物相比，开阔水域沉积物中的甲基化速率通常更高，后者处于阴凉和较凉爽的环境中。甲基化（r=0.76，p=0.034）和去甲基化（0.97，p=0.016）速率（天-1）均与温度呈正相关，但与大多数其他水质参数无关。水中的 MeHg 浓度与 pH 呈正相关（r=0.80，p<0.05），但甲基化速率仅略有相关（r=0.71）。驱动系统中微生物产生 MeHg 的环境因素包括温暖的温度、高水平的易生物降解的天然有机物，以及在较小程度上相对较低的 pH 值和水的停留时间。本研究还提供了基准数据，可以用来量化改变系统天然水流对汞甲基化和去甲基化速率的影响。
Zotero 插件
