A Simplified Drying Procedure for Analysing Hg Concentrations

Abstract

Mercury (Hg) in peatlands remains a problem of global interest. To mitigate the risks of this neurotoxin, accurate assessments of Hg in peat are needed. Treatment of peat that will be analysed for Hg is, however, not straightforward due to the volatile nature of Hg. The drying process is of particular concern since Hg evasion increases with the temperature. Samples are, therefore, often freeze-dried to limit Hg loss during the drying processes. A problem with freeze-drying is that cost and equipment resources can limit the number of samples analysed in large projects. To avoid this bottleneck, we tested if drying in a 60 °C-degree oven could be an acceptable alternative to freeze-drying. We both freeze-dried and oven-dried (60 °C) 203 replicate pairs of peat samples, and then examined the differences in total Hg concentration. The Hg concentration differed significantly between the two drying methods with a median Hg deficit in oven-dried samples of 4.2%. Whether a 4.2% deficit of Hg depends on one’s purpose. The lower median Hg concentration in oven-dried samples has to be weighed against the upside efficiently drying large sets of peat samples. By freeze-drying a subset of the samples, we fitted a function to correct for Hg loss during oven-drying (y= 0.96 x+ 0.08). By applying this correction, the freeze-drying bottleneck could oven-dry large-scale inventories of total Hg in peatlands with results equivalent to freeze-drying, but only have to freeze-dry a subset.