Impact of mining activities on soils and sediments at the historical mining area in Podljubelj, NW Slovenia

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Abstract

The abandoned Hg mine in Podljubelj was in operation with interceptions from 1557 to 1902. The entire operating period yielded about 110 000 tons of ore, from which 360 tons of Hg was produced. The objective of the research project was to establish the contents and spatial distribution of Hg in soils and stream sediments in the vicinity of the mine. On an area of 88 ha the soil was sampled in a 100 × 100 m grid. Two soil horizons (0–5 cm and 20–30 cm) were sampled in order to distinguish between geogenic and anthropogenic Hg sources. It was established that on an area of about 9 ha Hg content in soil exceeds The New Dutchlist action value for Hg (10 mg/kg). Total Hg concentrations in soil samples vary between 0.17 and 719 mg/kg, with a mean of 3.0 mg/kg. Mercury contents in stream sediments range from 0.065 to 1.4 mg/kg, with a mean of 0.64 mg/kg. The highest determined value in soils was found in the area around the former roasting furnace, where the ore was processed. Increased Hg concentrations were also found on the mine waste dump (108 mg/kg). Mercury contents in soils generally decrease with soil profile depth and with the distance from the mine and from the roasting furnace location. Mercury also appears in higher concentrations along the road that runs through the valley, which results from the use of Hg-bearing ore residues in road construction. The average enrichment factor (EF) of Hg in topsoil with respect to subsoil is 3.3. Calculated enrichment factors show higher values also for Cd (3.2), Pb (2.7), Ca (2.4) and P (1.9). The average enrichment factor of Hg in topsoil with regard to the established Slovenian soil averages (EFslo) is 19. EFslo of other determined chemical elements do not exceed 3.0.

Introduction

The Podljubelj Hg mine is situated in the NW part of Slovenia, in a narrow alpine valley near the border between Slovenia and Austria (Fig. 1, Fig. 2). Geographically, the area belongs to the Southern Alps (Karavanke) and has an agitated morphology. The ore deposit is located between 700 and 800 m above sea level in a narrow glacial valley. The basic climatic characteristics of the area are cold winters and cool summers. The annual average temperature is 8 °C, with the average of − 2.5 °C for January and 18 °C for July (Šipec, 1990). The prevailing soil types in the researched area are rendzinas and chromic cambisols. In the close vicinity of the roasting furnace and mine entrances, shallow skeleton soils have developed on top of the mine waste dump. The area is overgrown mostly with coniferous forest (Picea abies), and there are pastures in the valleys.

The ore deposit is of hydrothermal vein type, developed as a consequence of Middle Triassic (T22) volcanism (Drovenik et al., 1980). The ore appears in limestone, mostly as cinnabar in the form of small veins (Dimkovski, 1972). The exploitation of ore began in 1557 and it lasted for almost 500 years; the mine was finally abandoned in 1902. Because of the small ore bodies and low Hg concentrations in the ore (0.38% to 0.40% according to Dimkovski, 1972), the mine hardly covered the operation expenses. The entire operating period yielded about 110 000 tons of ore, from which 360 tons of Hg was produced. In 1855 a roasting furnace was set up near the mine. The waste material from the mine and the roasting furnace were dumped in the close vicinity of the mine. The total quantity of waste was estimated to approximately 170 000 tons (Mohorič, 1957). Most of this material was used for the construction of the Ljubljana–Celovec (Klagenfurt) road which runs through the valley.

The sources of Hg in the researched area are natural (geogenic) – ore-bearing limestone, and anthropogenic – dumps of barren material and roasting remains, atmospheric emissions and technological losses, and the use of the waste material in road construction and elsewhere. Hence, increased concentrations of Hg in the environment may be expected in the vicinity of the abandoned mine and roasting furnace.

The aim of the present study was to evaluate the reflection of past mining activities in the increased Hg contents in soils and sediments and to determine the spatial distribution of Hg in applied sampling materials in the narrow and wider area of the Podljubelj mine. Enrichment factors of all analyzed chemical elements were calculated in order to determine any other increased element content due to anthropogenic activities.

In the Podljubelj area some environmental studies were performed by the Nuclear Chemistry Department of the J. Stefan Institute from Ljubljana, Slovenia at the end of the 1970s. Investigations on mercury distribution, its uptake and assimilation in the environment by vegetation, animals and humans in Idrija and Podljubelj with respect to background values were performed by Kosta et al., 1972, Kosta et al., 1974, Stegnar (1973) and Stegnar et al. (1973). The average Hg content determined in soil (0–15 cm) in the vicinity of the Podljubelj mine was 655 mg/kg (Kosta et al., 1972). In the wider area of the mine Hg concentrations were between 3.11 and 10.1 mg/kg (0–5 cm) ( Stegnar, 1973), and between 7.1 and 35.1 mg/kg (0–15 cm) (Stegnar et al., 1973). In two samples of stream sediments, Hg contents of 0.15 and 0.16 mg/kg were found (Kosta et al., 1974).

The wider surroundings of the deposit were investigated also by Gnamuš et al. (2000) and Gnamuš (2002), who recorded the migrations and uptake of Hg in food chains in a ten-year study (1990–1999). Inorganic samples (soil, air) and samples of biota (vegetation, herbivorous species – roe deer and chamois goats, carnivorous species – lynxes and wolves) were analyzed from Idrija, Podljubelj and control localities. Mercury contents of soil measured at the former roasting furnace in Podljubelj were 469 mg/kg (404–550 mg/kg) (0–15 cm) and 522 mg/kg (438–571 mg/kg) (15–30 cm), and at the dump of barren material and roasting remains 18.0 mg/kg (12.5–27.0 mg/kg) (0–5 cm) and 48.2 mg/kg (41.2–59.0 mg/kg) (5–20 cm) respectively. Farther away from the abandoned mining–roasting location Hg levels in soil amounted to 16.3 mg/kg (0–10 cm) and 14.1 mg/kg (10–20 cm) (Gnamuš, 2002). Hg concentrations in the composite plant samples representing roe deer diet (10 samples) were relatively low, ranging from 0.11 to 1.74 mg/kg with an average of 0.58 mg/kg. In the organs of roe deer (two analyzed animals) the highest Hg content was found in kidney (101 and 209 ng/g fresh weight) (Gnamuš et al., 2000).

Our geochemical investigations in Podljubelj area began in 2003. Some preliminary results were published in Teršič et al., 2005, Teršič et al., 2006.

Section snippets

Materials and methods

The soil sampling was conducted in 2003 and 2004. 26 topsoil samples (0–5 cm) and 23 subsoil samples (20–30 cm) were collected within a research grid of 100 × 100 m in the vicinity of the mine and the roasting furnace (88 ha). Four additional soil samples were taken in the area of the abandoned ore furnace and waste material dump. Further 12 soil samples (0–5 cm) were collected farther away from the mine; these were used only for the construction of geochemical maps of spatial distributions of

Soil

Statistics for elemental contents in soil are given in Table 1.

The Hg average in soil determined from analyzed samples amounts to 3.0 mg/kg with individual contents ranging between 0.17 and 719 mg/kg. Mercury concentrations in topsoil vary from a minimum of 0.35 to a maximum of 244 mg/kg with the median of 3.7 mg/kg. In subsoil values are between 0.17 and 72 mg/kg with the median of 1.4 mg/kg. The highest determined Hg value, 719 mg/kg, was found in the area of the former roasting furnace where

Conclusions

The environmental impact of mining and ore processing around the Podljubelj Hg mine is spatially limited. Mercury contents are very high in the close vicinity of the past mining area and decrease with depth in soil profile and with the distance from the source of pollution. High Hg concentrations in the soil around the residues of the abandoned roasting furnace are a consequence of former atmospheric emissions and technological losses. They are sustained by a high proportion of organic matter

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