Metal mining and processing in the central Czech Republic has led to the contamination of surrounding soils and vegetation. In this study, Hg concentrations were measured in spruce (Picea abies L.) and beech (Fagus sylvatica L.) tree rings to monitor historical Hg deposition in the area. The highest Hg concentrations were found in spruce at an HgS smelting contaminated site (up to 15 ng g −1 ), probably reflecting smelting activities at the end of the nineteenth century. In the vicinity of a Pb smelter, Hg concentrations increased from the 1950s to maxima (up to 8.4 ng g −1 ) in the 1970s, corresponding with a peak of metallurgical production and smelter emissions in the mid 1970s. A decreasing trend in Hg concentrations since the 1980s was probably related to improvements in flue gas cleaning technologies. The beech trees, which grow at a site between two smelters and range in age from 150 to 220 years, seem to reflect deposition from both point sources. Mercury levels in beech trees were lower, that resulting from their greater distance from pollution sources, but the concentration trend was strongly correlated with metal production. Analysis of nutrient elements (Ca, Mg, K and Mn) in wood revealed environmental changes related to acid deposition, but a relation between concentration trends of nutrients and Hg was not found. This study shows that tree rings may be a good record of Hg deposition in areas affected by ore mining and smelting. Nevertheless, further investigation of Hg cycling in trees is necessary to satisfactorily interpret this particular historical Hg record.
Methods commonly used for soil sample preparation may be unsuitable for measuring Hg concentrations due to the possible loss of volatile Hg species when drying at higher temperatures. Here, the effects of freeze-drying, air drying at 25°C and oven-drying at 105°C on Hg concentrations in two soil types and three standard reference materials were tested. Two soils with different levels of Hg contamination and three reference materials were examined. A systematic decrease of Hg concentrations was observed in air-dried (24 %) and oven-dried (3 %) contaminated upland soils in comparison to freeze-dried control samples. The 105°C oven drying also led to loss of Hg from reference materials (5 %-8 % in comparison with the certified Hg concentration). Different results from the drying of sterilized reference materials and natural soils were probably related to the extent of microbiological activity, demonstrating the importance of this parameter in sample preparation for Hg analysis.
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