Mercury speciation in soils and river sediments of the industrialised Thur river catchment (Alsace, France)

Abstract
The mobility of mercury (Hg), particularly organic Hg, has been studied in the Thur river basin using an ultra-sensitive and specific analytical equipment (High Performance Liquid Chromatography (HPLC) with on-line CVAFS detection). The Thur river, sub-tributary of the Rhine river is polluted by mercury since the beginning of the 20th century because of industrial effluents from chlorine and soda industry. This study allows to determine in different environmental compartments (soils and river sediments) the total mercury contents (THg) and, for the first time in such an industrialized catchment, the methyl mercury concentrations (MeHg). The ratio between MeHg and THg concentrations is higher in the grassland soils than in the industrial and alluvial soils even if MeHg and THg contents are higher in these latters. The highest MeHg/THg ratios can be observed for lowest C/N ratios and slightly acidic soils. MeHg/THg ratio is very low in the industrial channel despite high MeHg and THg concentrations. For river sediments, MeHg/THg ratios are higher in the suspended matters than in the bottom sediments. These first results are very helpful to better understand the transformation of Hg species in the different compartments and the processes of Hg transfer from one compartment to another.