Soils from sites of historical metal mining in western Małopolska ( S Poland ) are strongly contaminated with Zn , Pb and Cd

Concentrations of Cd, Pb and Zn in soils developed at 63 sites of historical metal mining in western Małopolska (S Poland) were estimated. Heavy metal concentrations were measured with an atomic absorption spectrometer after wet digestion in hot HClO4 (total forms), extraction in 0.1 M BaCl2 (exchangeable forms) or in water (water-soluble forms). Basic soil properties such as texture, C, N, Ca contents and pH were also measured. Total concentrations of Cd in soil varied from 4.4 to 392, Pb from 72.8 to 16931 and Zn from 322 to 41860 mg kg. Exchangeable Cd, Pb and Zn extended from 0 to 19.3 %, from 0 to 0.2 % and from 0 to 3.5 % of the total metal forms, respectively, indicating that Cd is the most mobile and potentially bioavailable metal. In turn, water-soluble metal forms did not exceed 1 % of the total. Our study showed that soils developed at sites of historical metal mining are severely polluted with heavy metals. Old heaps threaten not only the environment, but also local inhabitants, as they are often located in a close proximity to houses or agricultural


Introduction
Western Małopolska is a part of one of the oldest region of non-ferrous metal mining in central Europe (Molenda 1963).Mining of Zn-Pb ores in western Małopolska dates back to 12 th century, although earlier exploitation cannot be excluded (Molenda 1963).During a few centuries, Pb and Ag were being used, whereas Zn ores were deposited in the form of heaps or left in mine shafts.Excavation of Zn ores started in the 16 th century, and since the 19 th century Zn has been the most important metal mined and processed in this region (Molenda 2000).Contemporary metal industry in this area developed after World War II, when modern metal mines and smelters had been built.High Cd, Pb and Zn concentration in soils in the nearby of these modern mines and smelters in western Małopolska is an effect of deposition of mining and flotation wastes as well as smelting emissions; the contamination is evident and well-studied by many authors (e.g.Chrastný et al. 2012, Stefanowicz et al. 2010, Verner et al. 1996).Relics of historical Pb-Zn mining (small, inconspicuous, probably at least 100 years old heaps) are more problematic.Most of them are spread in vast areas covered by forests.However, they can be also found in the immediate vicinity of houses, gardens or agricultural fields, potentially posing a threat to local inhabitants.The aim of our study was to identify objects of historical Ag-Pb-Zn mining (old mine waste heaps) in non-forested areas in western Małopolska and measure Cd, Pb and Zn concentrations in their soils.

Materials and Methods
Sixty-three study sites were established in the area of historical Ag-Pb-Zn mining between Krzeszowice, Libiąż, Jaworzno and Olkusz in western Małopolska (S Poland).They were located on S, SW or SE slopes of old mining heaps (Fig. 1).From each site, 3 samples of the top mineral layer to a depth of 15 cm were collected (2-3 m apart) and bulked to obtain one composite soil sample.Concentrations of Cd, Pb and Zn were measured by flame atomic absorption spectrometry (Varian 220 FS) after wet digestion in hot HClO 4 (total forms), extraction in 0.1 M BaCl 2 (exchangeable forms) or in water (water-soluble forms).Additionally, some basic soil properties were estimated.The particle size distribution (sand, silt and clay fractions) was determined by a combination of sieving and sedimentation.The content of organic C was measured with Leco RC-612 instrument, whereas total N by the Kjeldahl method using a Kjeltec 2300 (Foss

Results
Total concentrations of metals in soils varied widely: Cd from 4.4 to 392, Pb from 72.8 to 16931 and Zn from 322 to 41860 mg kg -1 (Table 1).Similarly, exchangeable and water-soluble metal concentrations also varied across a wide range (Table 1).Exchangeable Cd, Pb and Zn extended from 0 to 19.3 %, from 0 to 0.2 % and from 0 to 3.5 % of the total metal forms, respectively.In turn, water-soluble metal forms did not exceed 1 % of the total.Other soil properties such as texture, nutrient content or pH did not differ between soils as much as did heavy metal concentrations (Table 1).The soils were similar with respect to pH, which was relatively high in all samples, ranging from 7.1 to 8.1.It was positively correlated with Ca concentration in soil (r = 0.66, p < 0.0001), which was also high, reaching up to 323 g kg -1 .Although studied soils were all neutral or alkaline, pH significantly (p < 0.0001) affected the amount of exchangeable Cd (r = -0.61)and Zn (r = -0.66)concentrations in soil.Relations between pH and the ratio of exchangeable to total Zn and Cd are shown in Figs 2 and 3.The amount of water-soluble metals was not affected by pH (p > 0.1).

Discussion
Concentrations of Cd, Pb and Zn in almost all tested soils exceeded the maximum permissible guideline values (Cd: 1-3, Pb: 50-300, Zn: 150-300 mg kg -1 ; Commission of European Communities 1986).Metal concentrations in the most polluted soils from old mining areas exceeded the maximum permissible values from 56 (Pb) to 140 times (Zn).The soils developed on heaps were characterized by high Ca concentrations and high pH, as mining wastes contain large amounts of dolomite and calcite.Ore deposits near Olkusz comprise 69 % of dolomite and calcite (Cabała 2009).However, despite high pH, concentration of exchangeable, potentially bioavailable and toxic Cd form, exceeded in many soils 10-19 % of total Cd.Mobility of Zn and particularly Pb was low.The results are in accordance with those obtained by Kapusta et al. (2011) andVaněk et al. (2005), indicating that Cd is the most mobile of the three metal tested.
Our study showed that many relics of historical mining in western Małopolska are heavily contaminated with Cd, Pb and Zn.Therefore, old heaps may threaten not only the environment, but also local inhabitants, as they are often located close to houses or agricultural fields.The question remains to what extent the metals are taken up by plants growing on old heaps and in their vicinity, and incorporated into the trophic chain.Pyatt et al. (2001) found that metal may affect the environment for many centuries after cessation of the industrial activities.It should be taken into account that metal mining remnants, such as hillocks and mining shafts, as well as social awareness of metal pollution at such sites will probably disappear with time, while heavy metalsas elementsremain in soil, constantly posing a threat to the surroundings.

E3S
Web of Conferences DOI: 10.1051/ C Owned by the authors, published by EDP Sciences, This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2 0 , which .permits unrestricted use, distributi and reproduction in any medium, provided the original work is properly cited.on, Tecator).Soil pH was measured electrometrically after extraction with H 2 O. Concentration of total Ca was measured by flame atomic absorption spectrometry after wet digestion in hot HClO 4 .The data were transformed with a logarithmic or exponential function, standardized and subjected to correlation/regression analysis.