Environmental impacts of the abandoned mercury mine in Podljubelj, Slovenia

Abstract

senik’s tributaries. Each soil and sediment sample consisted of 5 sub-samples. The soil samples were gently crushed, then the fraction smaller than 2 mm was pulverized. In sediment samples we separated different fractions with dry sieving. Fraction smaller than 0,125 mm was analyzed. Analysis for 41 chemical elements was performed by inductively coupled plasma mass spectrometry (ICP-MS) after (total) four-acid digestion (mixture of HClO4, HNO3, HCl and HF at 200°C). Hg was determined by means of cold vapor atomic absorption spectrometry CV-AAS after aqua regia digestion (mixture HCl, HNO3 and water at 95°C). The reliability of analytical procedures was considered adequate for using the determined elemental contents in further statistical analyses. The universal kriging with linear variogram interpolation method (DAVIS, 1986) was applied to construct the maps of spatial distribution of particular elements in soil. For interpolation we considered 41 soil samples (0‐5 cm) from the narrow area of the former mine and smelter. Results The Hg average in soil determined from analyzed samples amounts to 3.04 mg/kg with individual contents ranging between 0.17 and 719 mg/kg. In topsoil Hg concentrations vary from minimum 0.35 to maximum 244 mg/kg with the median of 3.67 mg/kg. The subsoil median is 1.39 mg/kg and individual values between 0.174 and 71.7 mg/kg. The highest determined value (719 mg/kg) was found at the area of former smelter. The concentrations of mercury in soils generally decrease with depth in soil profile and with the distance from the mine. The average enrichment factor in topsoil with respect to subsoil is 3.3. Average contents of Hg in topsoil exceeded the estimated average for soil in Slovenia, which is 0,065 mg/kg (©AJN, 2003), more than 56-times, in subsoil the estimated average was exceeded about 21-times. The areal distribution of mercury in soil (Fig. 1) shows that the mercury halo is limited to the immediate surroundings of the smelter, while away from it the contents rapidly decrease. On an area of about 9 hectares the Hg contents in soil exceed the Slovenian critical value for soil (10 mg/kg). Examination of areal distributions reveals distinct distribution patterns also for Ca, Cd and P, as well as for additional 21 elements. Distributions of the latter may be divided in two groups that reflect the natural elemental distributions in dependence of geochemical composition of the local geology. Group 1 comprises the elements Zr, Th, Hf, K, Ce, La, Na, Rb, W, Ta, Nb, Al and Ba. Their combined distribution exhibits the highest values in the lowest parts of the studied area. The values decrease with altitude above the sea level. High group 1 element values are associated with the B horizon of brown soils on limestones and dolomites. Group 2 comprises the elements Sc, Cr, Ni, Co, Fe, Li, Ti and V. Their combined distribution is characterized by high values in hilly areas, there where the contents of group 1 ele