An analytical protocol for the determination of total mercury concentrations in solid peat samples

摘要

Traditional peat sample preparation methods such as drying at high temperatures and milling may be unsuitable for Hg concentration determination in peats due to the possible presence of volatile Hg species, which could be lost during drying. Here, the effects of sample preparation and natural variation on measured Hg concentrations are investigated. Slight increases in mercury concentrations were observed in samples dried at room temperature and at 30℃ (6.7 and 2.48 ng kg~(-1) h~(-1), respectively), and slight decreases were observed in samples dried at 60, 90 and 105℃ (2.36, 3.12 and 8.52 ng kg~(-1) h~(-1), respectively). Fertilising the peat slightly increased Hg loss (3.08 ng kg~(-1) h~(-1) in NPK-fertilised peat compared to 0.28 ng kg~(-1) h~(-1) in unfertilised peat, when averaged over all temperatures used). Homogenising samples by grinding in a machine also caused a loss of Hg. A comparison of two Hg profiles from an Arctic peat core, measured in frozen samples and in air-dried samples, revealed that no Hg losses occurred upon air-drying. A comparison of Hg concentrations in several plant species that make up peat, showed that some species (Pinus mugo, Sphagnum recurvum and Pseudeuernia furfuracea) are particularly efficient Hg retainers. The disproportionally high Hg concentrations in these species can cause considerable variation in Hg concentrations within a peat slice. The variation of water content (1.6% throughout 17-cm core, 0.97% in a 10X 10 cm slice), bulk density (40% throughout 17-cm core, 15.6% in a 10X10 cm slice) and Hg concentration (20% in a 10X10 cm slice) in ombrotrophic peat were quantified in order to determine their relative importance as sources of analytical error. Experiments were carried out to determine a suitable peat analysis program using the Leco AMA 254, capable of determining mercury concentrations in solid samples. Finally, an analytical protocol for the determination of Hg concentrations in solid peat samples is proposed. This method allows correction for variation in factors such as vegetation type, bulk density, water content and Hg concentration in individual peat slices. Several subsamples from each peat slice are air dried, combined and measured for Hg using the AMA254, using a program of 30 s (drying), 125 s (decomposition) and 45 s (waiting). Bulk density and water content measurements are performed on every slice using separate subsamples.