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Atmospheric Lead Pollution of Croatian Mountain Karst: Geochemical Mapping and Lead Isotope Evidence

High lead concentrations in soils of Croatian karst occur on the sharp geomorphological boundary where the Mediterranean climate abruptly changes into a cold continental climate. These were determined by geochemical baseline mapping of the topsoil cover in the Croatian karst regions of Istria, Gorski kotar, Kvarner and Lika which was performed through the analysis of over 800 sampling sites. A total of 25 major and trace elements including (Mo, Cd, Pb, Zn, As, Ni, Cu, Co) was analyzed by ICP-AES and Hg by FAAS. Lead isotope ratios were determined on selected soil and sediment profiles by ICP-MS. The patterns of geochemical distributions of Pb, Hg, Cd, and total S in topsoil indicate anomalous concentrations in the Gorski kotar and Velebit Mountain regions. The anomalies (especially Pb) overlap with the contours of mean annual precipitation of more than 2500 mm, indicating an association of these elements with airborne contamination. The Gorski kotar region of the Dinaric Alps is one of the most anomalous wet zones, which exhibits the highest mean precipitation values in the mesoscale climatology of the Alpine region. The detected high Pb contents and their spatial distribution in topsoil obtained during the geochemical baseline survey of topsoil in Croatia are in correspondence with precipitation anomalies (Fig. 1). The most striking difference is expressed by Pb in samples taken at altitudes higher than 1000 m above sea level, where most samples have concentrations above 80 mg/kg, which is almost twice the median content of lead (38 mg/kg) in the whole region. Detailed studies of the Pb distribution in the soil profiles showed concentrations of lead in remote regions up to 200 mgkg-1 in the upper 4 cm of the soil profiles.The isotopic ratio 206Pb/207Pb in all topsoil samples (0-10 cm depth), from both remote sites and those close to major roads, has a narrow range from 1.18 to 1.185 despite that samples taken at depths of >25 cm show a much wider range (from 1.21 to 1.32).

Lead; pollution; topsoil; geochemical mapping; stable isotope ratios.

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