Chromium and nickel distribution in soils, active river, overbank sediments and dust around the Burrel chromium smelter (Albania)
Introduction
Chromium occurs as a trace element in many minerals, but the only mineral of commercial importance is chromite [(Mg,Fe)(Al,Cr,Fe)2O4]. Its simplified mineralogical composition is FeCr2O4. In chromite ore, the Cr2O3 oxide content varies between 15% and 65%. Estimated annual world consumption of chromium is about 12.5 million tonnes of which 85% are consumed by metallurgy, 8% by chemicals, and 7% by refractories (Darrie, 2001).
Albania has been an important chromite producing country, since major podiform chromite deposits occur mainly in the eastern ophiolite belt. It occupied the world's third place in chromium ore production until 1991, before the industry collapsed due to major political changes in the early nineties (Perron, 1995). The absence of any environmental legislation until 1990 and due to economical considerations, mining and industrial sites were severely polluted. However, no detailed data on the total pollutant content in different sampling media exists. Apart from the total content, element speciation is important, particularly for chromium, since it can exist in the environment in two stable oxidation states, namely Cr(III) and Cr(VI). Cr(III) is considered to be an essential trace element for the functioning of living organisms. According to Bartlett and Kimble (1976) chromium might control the glucose, known as glucose tolerance factor (CrGTF). Cr in soils and rocks occurs mostly as chromite which is extremely insoluble (Becquer et al., 2003). Cr(VI) is toxic and easily soluble and is an acute irritant of living cells (James, 1996). Skin contact induces allergies (Yassi and Niober, 1988). Furthermore it is carcinogenic to humans via inhalation (Whalley et al., 1999). Concentrations of Cr(VI), as low as 0.5 mg/kg in solution and 5 mg/kg in soils can be toxic to plants (Turner and Rust, 1971). Elevated Cr concentrations often are associated with other heavy metals such as Ni which in high concentrations might pose human and eco-toxicological concern.
Ferrochromium, slags as well as gas–dust emissions are the final by-products of the smelter and obviously form a potential point source for pollution (see for example Macklin and Dowsett, 1989, Maskall et al., 1995). Furthermore, in the study area the slags have been used in local road construction causing a widespread contamination. Areal contamination can also be due to spreading of wind blown dust particles, originating directly from the smelter chimneys or from slag dumps. Finally, additional spread of contaminants can occur along rivers which drain the industrial areas (Wolfenden and Lewin, 1977, Swennen et al., 1994).
The aim of this study is to map the areal distribution particularly of Cr and Ni, but also of associated heavy metals (Zn, Co, Cu) in different sampling media (i.e. soils, river and overbank sediments as well as dust) around the Burrel industrial site. To be able to fully assess the degree of contamination, local background concentrations in the different sample media were analyzed. Attention had to be paid to the fact that two geological substrates dominate the study area. Serpentinite rocks form the hilly substrate west of the smelter while Pliocene gravel/sand occur in the plain around the smelter site and downstream of this potential contamination source. In addition, possible atmospheric contamination has to be taken into account. To define local background values, soil and substrate samples were analyzed above and within serpentinite and Pliocene gravel/sand at a distance 3–8 km from the smelter. Additionally active stream sediments as well as overbank from several locations upstream of the smelter in an area with similar geological substrate as encountered near the smelter were analyzed. Overbank samples were especially taken since, according to Ottesen et al. (1989) and Swennen et al., 1994, Swennen et al., 1996, samples taken at depth can record pristine or at least pre-industrial values within specific catchment areas.
Section snippets
Overall setting and Cr smelting industry
Albania is situated in the western part of the Balkan Peninsula (i.e. east of Adriatic and Ionic Seas). About 50% of the territory has an elevation situated between 200–1000 m, while the rest corresponds to lowland areas (e.g. Periadriatic Depression). Its climate is typically Mediterranean, with moderate and wet winters and very hot and dry summers (ASHRSH-QSGJ, 1990).
Albania is made up of different geological units, which are grouped in the Albanides (Fig. 1A). In the central and eastern part
Deduction of local background concentrations
Since geochemical signatures in soils and sediments are lithology-dependent (Hawkes and Webb, 1962, Levinson, 1974), first local background values will be discussed.
Lithogeochemical data of the Serpentinite and Pliocene substrata and overlying soils are given in Table 1. Due to the limited number of samples analyzed it is impossible to report on local threshold values. Average concentrations for Cr and Ni in the studied Serpentinite rocks are 1625 and 1515 mg/kg, respectively. These values are
Conclusions
The data gathered from soils, active river and overbank sediments and dust samples around the Burrel smelter, shows that in all sampling media a clear signal can be deciphered reflecting pollution by the industrial activities. However the study also showed that there is a need to define local background concentrations. This is of especial importance in evaluating the soil geochemical signatures, otherwise soils developed upon ultramafic rocks could be wrongly classified as polluted.
Acknowledgments
We acknowledge the assistance of Dany Coetermans from the Fysico-chemische Geologie during the laboratory work as well as Prof. Geoffrey King whom comments helped to improve the English. The comments of the reviewers helped in improving the quality of the manuscript. The research was realized with the financial support of the Katholieke Universiteit of Leuven, East European Initiatives, Project 3E000659.
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