Jackson Brian, Taylor Vivien, Baker R Arthur, Miller Eric
Trace Element Analysis Core, Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA.
Environ Sci Technol. 2009 Apr 1;43(7):2463-9. doi: 10.1021/es802656p.
Atmospheric deposition of anthropogenic Hg has led to increased Hg concentrations in many ecosystems. Modeling is an effective method for predicting the complex dynamics of Hg transport in watersheds. Such models require accurate concentrations of water column methylmercury, CH3Hg+, for input parameters, yet these concentrations are very difficult to measure precisely because they are so low. We developed a method for aqueous CH3Hg+ quantification in Lake Champlain, VT, where ambient CH3Hg+ concentrations are < 0.04 ng L(-1). The analysis utilized species-specific isotope dilution, purge and trap gas chromatography inductively coupled plasma mass spectrometry and provided instrument detection limits of about 0.3 fM (0.06 pg L(-1)) and method detection limits of 15 fM (0.003 ng L(-1)) for CH3Hg+, which are among the lowest reported. Artifactual methylation of inorganic Hg(2+) was shown to be minor, and the precision of the isotope dilution method was generally <5% relative standard deviation, which is much lower than would have been the case for an external calibration approach. The method is accurate even at low concentrations of 0.025 ng L(-1). This combination of precision, accuracy, and low detection allows for quantification of significant differences in CH3Hg+ concentration between bays and over time within bays of Lake Champlain, where mean CH3Hg+ concentrations differ by only 0.006 ng L(-1) at concentrations as low as 0.014 ng L(-1).
人为汞的大气沉降导致许多生态系统中的汞浓度升高。建模是预测流域汞迁移复杂动态的有效方法。此类模型需要准确的水柱甲基汞（CH3Hg+）浓度作为输入参数，但这些浓度很难精确测量，因为它们非常低。我们开发了一种用于佛蒙特州尚普兰湖水中CH3Hg+定量的方法，该湖环境CH3Hg+浓度<0.04 ng L(-1)。该分析采用物种特异性同位素稀释、吹扫捕集气相色谱电感耦合等离子体质谱法，对CH3Hg+的仪器检测限约为0.3 fM（0.06 pg L(-1)），方法检测限为15 fM（0.003 ng L(-1)），这是已报道的最低值之一。结果表明，无机Hg(2+)的人为甲基化程度较小，同位素稀释法的精密度一般相对标准偏差<5%，远低于外部校准方法的情况。该方法即使在0.025 ng L(-1)的低浓度下也很准确。这种精密度、准确度和低检测限的组合能够定量尚普兰湖不同海湾之间以及海湾内不同时间CH3Hg+浓度的显著差异，在浓度低至0.014 ng L(-1)时，平均CH3Hg+浓度仅相差0.006 ng L(-1)。
