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

Abstract

In the region of north-western Croatia (NWC) 328 topsoil sampleswere taken (from a depth of 0 to 25 cm). The composite sampleswere analyzed after near total decomposition (a hot acid mixture:HClO4–HNO3–HCl–HF at 200°C) by ICP–AES for As, Cd, Cu, Pband Zn. Hg was analysed by cold vapour AAS. The following elementconcentration ranges were acquired: As 2–74 mg/kg (geometricmean 8 mg/kg), Cd 0.4–9.4 mg/kg (geometric mean 0.4 mg/kg), Cu5–248 mg/kg (geometric mean 22 mg/kg), Hg 5–4,535 mg/t (geometricmean 55 mg/t), Pb 15–699 (geometric mean 32 mg/kg) and Zn28–1,432 (geometric mean 82 mg/kg).The analysis of the spatial distribution of heavy metals in NWCshowed increased values of As, Cd, Hg and Pb at Mts. Žumberak,Medvednica, Ivanščica and Kalnik that originate mainly from naturalsources (bedrock mineralizations and ore deposits). The Cu and Zncontents 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 ofanthropogenic origin and are related to wine-growing areas.In the Sava River valley the average levels of Hg, Zn, As, Cd,and Pb are higher than the calculated baseline values (geochemicalbackground) in the NWC while the Cu values are equal to thebaseline values. The higher values of As, Cd, Pb, and (in part) Zn arefor the most part of anthropogenic origin, and to a lesser extent ofnatural origin. The Hg in the topsoil has a strong anthropogenic influencecaused 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 Znat a depth of 20 cm is almost half the content of the same elementsfound in the first two centimeters of the soil. At a depth of 60 cm, theconcentrations are in the level of background values characteristic ofthe preindustrial era.When compared to the calculated baseline values, the contents ofAs, Cd, Cu and Hg in the soils of the Drava River valley are higher,while the Pb and Zn contents are anomalous. According to permittedconcentrations of heavy metals for ecological food productionprescribed by Government regulations the contents of As, Pb andZn in the topsoil on the Drava alluvial sediment are too high. TheCu concentrations are lower than the limit permitted by Governmentregulation. The higher contents of mercury, although under the limitprescribed by Government regulation, are an immediate consequenceof fossil fuel combustion and traffic in the urban area of the city ofVaraždin. Factor analysis and high correlation coefficients show amutual connection of Pb, Zn and Cd (Pb and Zn r = 0.96; Pb and Cdr=0.80; Zn and Cd r=0.84). These 3 heavy metals show high positivefactor loadings on the first factor (F1) which accounts for more than58% of the data variability. The flood waters of the Drava River werehighly loaded with anthropogenic Pb, Zn and Cd mainly as a consequence of mining, smelting and flotation activities upstream in theMeža valley in the Republic of Slovenia and Austria. Also, they wereadditionally loaded with waste waters from upstream settlements. Thesoil profile shows that increasing depth results in the lowering of thePb, Zn, Cd and As content reaching the background level of that areaat 80 cm depth. This suggests that the alluvial sediments of the preindustrial era lay deeper.