Distribution of Pb, Sr, U isotopic signature and multielement composition of sediment in Lake Balaton (Hungary) at a sediment trap deep dredged 40 years ago near Balatongyörök – Search for routes of recent pollution

Abstract We studied the Pb, Sr, U isotopic composition and the concentration of toxic elements in sediment core samples collected in Lake Balaton at a sediment trap that was deep dredged in 1979, to analyze their changes in the last 40 years. Pb isotopic composition profiles of cores taken from the sediment trap showed a shift in 206Pb/207Pb from 1.206 ± 0.002 to 1.185 ± 0.002 going from bottom towards the top of the sediment, at 80–100 cm depth. Concomitantly Pb concentration together with Zn, Sb, Cu, Cd and Fe showed elevated, 2–4 times higher values in the top phase of the sediment. Calculated Pb isotopic composition of pollutant Pb fraction was 1.177 ± 0.005 in the case of the 206Pb/207Pb and 2.456 ± 0.004 for 208Pb/207Pb, which shows good agreement with literature data for lead ores in Poland and Germany, but it is distinct from literature data for leaded fuel concerning Middle and Eastern Europe. The marked change of the Pb signatures enabled the construction of a sediment deposition rate map. U and Mo showed a characteristic concentration peak in positioned exactly at the depth of Pb signature transition. Isotopic signature of U based on 234U and 235U also showed similar pattern. We suggest that the deposition of U and Mo can be related to cyanobacterial blooms in Lake Balaton in late1970s and early1980s.