ARSENIC AND HEAVY METALS IN BOTTOM SEDIMENTS OF KACZAWA WATERSHED IN SURROUNDING OF POLYMETALLIC ORE DEPOSITS ?ELE?NIAK (KACZAWSKIE MTS., SW POLAND)

Through the centuries, Lower Silesia was an important mining region. Local polymetallic copper deposits belong to the biggest in the world. The mining of certain minerals, including gold, copper, and nickel, is associated with acid drainage problems that can cause long-term impairment to waterways and biodiversity (Akcil and Koldas, 2006). Oxidation of pyritic ores is a major cause of acidic drainage (Bednar et al., 2005; Black and Craw, 2001; Gault et al., 2001). The production of iron(III) and hydrogen ions can catalytically dissolve secondary minerals, thereby increasing the metal load to the drainage (Wildeman et al., 1974; Plumlee et al., 1993). The study was carried out in the surrounding of old copper and arsenic mine “?ela?niak” in the Kaczawskie Mountains where metals were mined and smelted beginning from 15th century until 1925. Arsenic smelter operated in the village Radzimowice, situated on the slopes of ?ela?niak, until 1892. The main goal of the study was to examine the occurrence of arsenic and heavy metals and their concentrations in bottom sediments of the main streams draining the area. The samples were collected in the years 2002 and 2003 at 16 sites. Basic properties of sediments, i.e. pH, organic carbon grain size distribution, as well as As and heavy metal concentrations were determined. Most of the collected samples had sandy or gravel texture. pH was alkaline and the amount of organic carbon varied from 0,3 to 4,4 %. For As and heavy metal concentrations, only fine earth fraction of sediments (< 1mm) was examined. Concentrations of As and all metals examined were higher than natural background in Poland, which resulted from long-term sedimentation of the particles transported by the water. The highest concentrations of As were determined in the sediments of Olszanka stream (16 000 mg*kg-1 in 2002 and 9630 mg*kg-1 in 2003), that contained additionally the highest concentrations of other heavy metals – Cu (5920-6140 mg*kg-1), Zn (1240-1560 mg*kg-1), Pb (762-845 mg*kg-1), Ni (197 – 221 mg*kg-1) and Cd (3,4 mg*kg-1). Concentrations of metals and As decreased down the streams and were correlated with concentrations of iron oxides, which should be considered as typical for AMD-affected freshwaters (Karczewska et al. 2007). Almost 86 % of As, 78 % of Cu and 56 % of Ni was in potentially soluble forms. The correlations between total and potentially soluble forms of metals and As were not statistically relevant. As and heavy metals were also determined in particular grain size fractions of bottom sediments. Clay fraction (< 0,002 mm) contained the highest amounts of As and other metals. Sequential extraction of As (Wenzel et al. 2001) showed that the main forms of arsenic in the sediments were those occluded in amorphous and crystalline iron oxides. Speciation of other metals, carried out according to Zeien and Brummer (1991), showed various patterns that depended on the metal examined. Conclusions: 1) Concentrations of As and all metals examined near old copper and arsenic mine were higher than natural background in Poland. 2) Concentrations of metals and As decreased down the streams and were correlated with concentrations of iron oxides, which should be considered as typical for AMD-affected freshwaters. 3) Most of the As and heavy metals were in the soluble forms, bioavailable for plants and animals.

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