Anthropogenic lead in soils and lake sediments from the Croatian karst

Atmospherically introduced high lead concentrations in soils of Croatian karst occur along the sharp geomorphological boundary along which the Mediterranean climate abruptly changes into a cold continental climate. To trace the history of anthropogenic, atmospheric lead pollution, analysis of soils from the region as well as cores from the karst lake Vrana on the island of Cres were performed. The area affected Pb pollution covers most of the mountain karst region. Detailed studies of the Pb distribution in the profiles showed concentrations of lead in remote regions up to 200 mgkg-1 in the upper 4 cm of the soil profiles. The changes in soil chemistry due to acid rain deposition were determined with the aid of Al, Fe, Si, Mn phase extractions. Water extractable Pb concentrations from up to 727  ; gL-1 in the top horizons usually fall to less than 5  ; gL-1 at depths below 25 cm. The isotopic ratio 206Pb/207Pb in all topsoil samples from both remote sites and those close to major roads, has a narrow range from 1.18 to 1.185. Samples taken at depths of 1m show a much wider range from 1.21 to 1.32. Road side and sinkholes soils, have 206Pb/207Pb ratios from 1.125 to 1.14 a direct influence of petrol-lead. The lake sediments in a 80 cm long core show a 206Pb/207Pb ratio decline from 1.24 to 1.17 in the upward direction, reflecting the low ratio in modem aerosols. Using both total and mobile Pb (and other selected elements) concentrations in soils and the difference in lead isotope ratios in a sensitive karst environment, where a major part of pollution occurs through atmospheric deposition, it was possible to gain insight to both the history and the extent of lead pollution in this part of the Mediterranean region.