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Heavy Metal (As, Cd, Cu, Hg, Pb, and Zn) Distribution in Topsoil Developed on Alluvial Sediments of the Drava and Sava Rivers in NW Croatia

In the region of north-western Croatia (NWC) 328 topsoil samples were taken (the Amo-mollic horizon, from a depth of 0 to 20 cm). The composite samples were analyzed after near total decomposition (a hot acid mixture: HClO4-HNO3-HCl-HF at 200 C) by ICP-AES for As, Cd, Cu, Pb and Zn. Hg was analysed by cold vapour AAS. The following element concentration ranges were acquired: As 2-74 mg/kg (geometric mean 8 mg/kg), Cd 0.4-9.4 mg/kg (geometric mean 0.4 mg/kg), Cu 5-248 mg/kg (geometric mean 22 mg/kg), Hg 5-4 535 mg/t (geometric mean 55 mg/t), Pb 15-699 (geometric mean 32 mg/kg) and Zn 28-1 432 (geometric mean 82 mg/kg). The analysis of the spatial distribution of heavy metals in NWC showed increased values of As, Cd, Hg and Pb at Mts Žumberak, Medvednica, Ivanščica and Kalnik that originate mainly from natural sources (bedrock mineralizations and ore deposits). The Cu and Zn contents on Mt. Medvednica are only slightly less natural in origin. The high concentrations of copper on the slopes of Mts. Žumberak, Medvednica, Kalnik and in the NW part of Hrvatsko Zagorje are of anthropogenic origin and are related to winegrowing areas. In the Sava River valley the average levels of Hg, Zn, As, Cd, and Pb are higher than the calculated baseline values (geochemical background) in the NWC while the Cu values are equal to the baseline values. The higher values of As, Cd, Pb, and (in part) Zn are for the most part of anthropogenic origin, and to a lesser extent of natural origin. The Hg in the topsoil has a strong anthropogenic influence caused by mining upstream (Litija) and by the city of Zagreb’ s urban area (fossil fuel combustion, traffic, electrolysis, diverse paints, pharmaceutical products, chlor-alkali industry and paper industry). The pedogenic profile shows that the content of Cd, Pb, Cu and Zn at a depth of 20 cm is almost half the content of the same elements found in the first two centimeters of the soil. At a depth of 60 cm, the concentrations are in the level of background values characteristic of the preindustrial era. When compared to the calculated baseline values, the contents of As, Cd, Cu and Hg in the soils of the Drava river valley are higher, while the Pb and Zn contents are anomalous. According to permitted concentrations of heavy metals for ecological food production prescribed by Government regulations the contents of As, Pb and Zn in the topsoil on the Drava alluvial sediment are too high. The Cu concentrations are lower than the limit permitted by Government regulation. The higher contents of mercury, although under the limit prescribed by Government regulation, are an immediate consequence of fossil fuel combustion and traffic in the urban area of the city of Varaždin. Factor analysis and high correlation coefficients show a mutual connection of Pb, Zn and Cd (Pb and Zn r=0.96 ; Pb and Cd r=0.80 ; Zn and Cd r=0.84). These 3 heavy metals show high positive factor loadings on the first factor (F1) which accounts for more than 58% of the data variability. The flood waters of the Drava river were highly loaded with anthropogenic Pb, Zn and Cd mainly as a consequence of mining, smelting and flotation activities upstream in the Meža valley in the Republic of Slovenia and Austria. Also, they were additionally loaded with waste waters from upstream settlements. The soil profile shows that increasing depth results in the lowering of the Pb, Zn, Cd and As content reaching the background level of that area at 80 cm depth. This suggests that the alluvial sediments of the pre-industrial era lay deeper.

Geochemical mapping ; Topsoil ; Alluvial sediments ; Heavy metals ; NW Croatia

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