The distribution of total and methylmercury concentrations in soils near the Idrija mercury mine, Slovenia, and the dependence of the mercury concentrations on the chemical composition and organic carbon levels of the soil |
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Authors: | Takashi Tomiyasu Akito Matsuyama Ryusuke Imura Hitoshi Kodamatani Junko Miyamoto Yuriko Kono David Kocman Jo?e Kotnik Vesna Fajon and Milena Horvat |
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Institution: | (1) Graduate School of Science and Engineering, Kagoshima University, Korimoto Kagoshima, 890-0065, Japan;(2) National Institute for Minamata Disease, Minamata Kumamoto, 867-0008, Japan;(3) Department of Environmental Sciences, Institute Jožef Stefan, 1001 Ljubljana, Slovenia |
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Abstract: | Although the mining activity of the Idrija mine in Slovenia ceased in 1995, a large amount of mining dregs containing high
concentrations of mercury remains in the area. The mining dregs were transported with river flow and deposition along the
Idrija River. To estimate the dispersion and change in the chemical form of mercury, a total of 28 soil core samples were
taken around the river. The individual core samples were separated into layers for the analysis of their chemical composition,
carbon contents, total mercury (T-Hg) and methylmercury (MeHg) concentrations. The chemical composition measured by X-ray
fluorescence spectrometry was useful to estimate the dispersion of tailings: the fluvial terrace soil had a chemical composition
similar to that of the tailings and could be distinguished clearly from the forest soil. The highest T-Hg concentration, 1,100 mg kg−1, was observed in the fluvial terrace soil near the mine. Although the concentration decreased gradually along with distance
from the mine, concentrations higher than 200 mg kg−1 of T-Hg were still observed in the fluvial terrace soil approximately 20 km downstream from the mine. In the vertical distribution
of T-Hg in the hillslope soil, a higher value was observed in the upper layers, which suggests the recent atmospheric deposition
of mercury. The concentration of MeHg was the lowest at the riverside and higher in the hillslope soil, which was the opposite
of the T-Hg distribution. The total organic carbon content tracked similarly with the distribution of MeHg and a linear relation
with a significantly high correlation coefficient was obtained. The distinction may be related to the different dispersion
process of mercury, and the organic carbon contents may be an important factor for MeHg formation. |
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