Determination of mercury in polluted soils surrounding a chlor-alkali plant: Direct speciation by X-ray absorption spectroscopy techniques and preliminary geochemical characterisation of the area Original Research Article

Soil samples collected in the surroundings of a chlor-alkali plant in the Netherlands were characterised by synchrotron-based techniques and conventional analytical procedures, in order to evaluate the environmental impact of Hg emissions and other heavy metals present in these locations. Analysis of total metal content by inductively coupled plasma-optical spectroscopy (ICP-OES) revealed a heterogeneous contamination of Hg, with concentrations ranging from 4.3 to 1150 μg g−1. In addition, significant concentrations of Cu, Ni, Pb, Zn, Mn and principally Fe were also identified within the studied samples. Direct determination of mercury species by X-ray absorption near edge spectroscopy (XANES) showed inorganic Hg compounds to prevail in all soils, being Cinnabar (HgSred) and Corderoite (Hg3S2Cl2) the main species. Nevertheless, more soluble mercury compounds, such as HgO and HgSO4, have been also identified in significant proportion (from 6 to 20% of total mercury content), indicating a potential risk of mercury mobilisation. On the other hand, the application of sequential extraction schemes (SES) revealed large portions of weakly available Hg extracted in the residual fraction, while Hg associated to the exchangeable phase amounts as much as 19% of total Hg, thus, supporting the results obtained by XANES.