engleski

Distribution and behavior of selected elements in soil ver a historical Pb-Ag mining site at Sv. Jakob, Croatia

The geochemical patterns of certain elements (Pb, Zn, Cd and Hg) in soils from the floodplain of the river Sava and some tributaries that drain Mt. Medvednica NW of Zagreb, Croatia, obtained during an environmental regional geochemical study indicated that the sources of pollution were not only from Pb-Hg-Ba mining region situated along the upper course of the river Sava in neighboring Slovenia, but also in part from local historical mining sites located on Mt. Medvednica. As a target of this study was an old 17 century lead mine (galena with 485 ppm of Ag) situated near the chapel of St. Jacob (Croatian Sv. Jakob) on the crest of Mt. Medvednica (830m a.s.l.). The mineralization which consists of galena, sphalerite, pyrite and quartz occurs as irregular veins within Triassic dolomites. A total of 110 brown forest topsoil (0-25 cm) soil samples was collected on dense regular grid covering an area of approximately 1.5 km2. Ten samples were selected for detailed chemical and mineralogical analysis. Trace metal values were obtained from aqua regia extracts, while their residence sites in soils were identified by sequential extraction performed with the aid of a modified combination of procedures proposed by Tessier et al., (1979) and Hall et al., (1996). The following phases were defined by the reagents used: exchangeable, carbonate, iron and manganese oxide, organic-sulphidic and residual. The concentration trace metals in resulting solutions was determined by atomic adsorption spectroscopy and inductively-coupled plasma spectrometry. Total mercury was determined by flameless AAS mercury detector (AGP-1) from solid samples after heating at 700°C and pre-concentration with a gold wire (detection limit = 10 ngg-1).The aqua regia extractable Pb values varied from 9 to 18000 mgg-1, Zn 12-9000 mgg-1, Cd from <0.1 to 180 mgg-1, and total Hg from 10 ngg-1 1800 ngg-1. The distribution of these elements in soil indicates their inherited and undisturbed geochemical relationship to the mineralization. The importance of each of the phases for the trace metals studied obtained by sequential extraction in soil samples with high total contents is: a) Pb carbonate > Fe and Mn oxide> organic-sulphide> exchangeable = residual b) Zn organic-sulphide> Fe and Mn oxide> residual> carbonate> exchangeable c) Cd Fe and Mn oxide>carbonate=organic-sulphide> exchangeable>residual The mineralogy of the soils is dominated by quartz, mica, geothite, kaolinite and plagioclase, cerrusite was identified by XRD only in one sample and no primary sulphide minerals (galena) were found. The flooding of the river Sava (the last major flood occurred in 1964) is the major source of soil pollution in the floodplain area south of Zagreb, but the violent mudflows from streams that drain the areas of historical mining sites that occur after rainstorms and flood northwestern parts of the city, as this study shows, also present a probable source of pollution.

selective sequential extraction; X-ray diffraction; soil pollution; Pb-Ag mining

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