Distribution of mercury, methyl mercury and organic sulphur species in soil, soil solution and stream of a boreal forest catchment
Distribution of mercury, methyl mercury and organic sulphur species in soil, soil solution and stream of a boreal forest catchment
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DOI：
10.1023/a:1024904502633
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发表时间：
2003
期刊：
影响因子：
4
通讯作者：
U. Skyllberg;J. Qian;W. Frech;K. Xia;W. Bleam
中科院分区：
文献类型：
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作者：
U. Skyllberg;J. Qian;W. Frech;K. Xia;W. Bleam
测定了瑞典北部一小片北方森林集水区土壤、土壤溶液和溪流中甲基汞、CH3汞(II)、总汞、Hgtot=CH3 Hg(II)+Hg(II)和有机硫的浓度。CH3Hg(II)/Hgtotratio从泥炭质河岸土壤的1.2-17.2%下降到距溪流20米的矿物和泥炭土壤的0.4-0.8%，表明汞(II)的净甲基化条件在靠近溪流的河岸带最有利。土壤和土壤溶液中CH3Hg(II)的结合量与土壤溶液中的Hgtotin浓度呈显著正相关。这一点，以及土壤溶液中的CH3Hg(II)/Hgtotratio高于土壤中的事实，可能表明土壤溶液中的Hg(II)比土壤结合的Hg(II)更有利于甲基化过程。采用S K边X射线吸收近边结构(XANES)光谱对土壤、土壤浸出物和溪流有机质样品中的还原有机S官能团进行了定量研究。Org-SRED可能代表RSH、RSSH、RSR和RSSR功能，占所有受检样本中S总数的50%到78%。在10个土壤样本中只有1个土壤样本中检测到无机硫化物[例如FeS_2(S)]，没有一个溪流样本中检测到无机硫化物。模型计算表明，在氧化条件下，土壤、土壤溶液和溪水中几乎100%的汞(II)和CH3汞(II)被硫醇基团(RSH)络合。在pH为5时，土壤溶液中游离CH3Hg2+和Hg2+离子的浓度分别约为10−18和10−32M。对于CH3Hg(II)，当无机硫化物浓度高于10−9M时，无机双硫化物络合物可能有助于总溶解度，而增加汞(II)的溶解度需要相当高的无机硫化物浓度(较低的氧化还原电位)。
Concentrations of methyl mercury, CH3Hg (II), total mercury, Hgtot= CH3Hg (II) + Hg (II), and organic sulphur species were determined in soils, soil solutions and streams of a small (50 ha) boreal forest catchment in northern Sweden. The CH3Hg (II)/Hgtotratio decreased from 1.2–17.2% in the peaty stream bank soils to 0.4–0.8% in mineral and peat soils 20 m away from the streams, indicating that conditions for net methylation of Hg (II) are most favourable in the riparian zone close to streams. Concentrations of CH3Hg (II) bound in soil and in soil solution were significantly, positively correlated to the concentration of Hgtotin soil solution. This, and the fact that the CH3Hg (II)/Hgtotratio was higher in soil solution than in soil may indicate that Hg (II) in soil solution is more available for methylation processes than soil bound Hg (II). Reduced organic S functional groups (Org-SRED) in soil, soil extract and in samples of organic substances from streams were quantified using S K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Org-SRED, likely representing RSH, RSSH, RSR and RSSR functionalities, made up 50 to 78% of total S in all samples examined. Inorganic sulphide [e.g. FeS2(s)] was only detected in one soil sample out of 10, and in none of the stream samples. Model calculations showed that under oxic conditions nearly 100% of Hg (II) and CH3Hg (II) were complexed by thiol groups (RSH) in the soil, soil solution and in the stream water. Concentrations of free CH3Hg+and Hg2+ions in soil solution and stream were on the order of 10−18and 10−32M, respectively, at pH 5. For CH3Hg (II), inorganic bi-sulphide complexes may contribute to an overall solubility at concentrations of inorganic sulphides higher than 10−9M, whereas considerably higher concentrations of inorganic sulphides (lower redox-potential) are required to increase the solubility of Hg (II).