Lead isotope ratios in tree bark pockets: An indicator of past air pollution in the Czech Republic

Tree bark pockets were collected at four sites in the Czech Republic with differing levels of lead (Pb) pollution. The samples, spanning 1923-2005, were separated from beech (Fagus sylvatica) and spruce (Picea abies). Elevated Pb content (0.1-42.4 mu g g(-1)) reflected air pollution in the city of Prague. The lowest Pb content (0.3-2.6 mu g g(-1)) was found at the Kosetice EMEP "background pollution" site. Changes in (206)pb/Pb-207 and (208)pb/Pb-206 isotope ratios were in agreement with operation times of the Czech main anthropogenic Pb sources. Shortly after the Second World War, the (206)pb/Pb-207 isotope ratio in bark pockets decreased from 1.17 to 1.14 and the (208)pb/Pb-206 isotope ratio increased from 2.12 to 2.16. Two dominant emission sources responsible for these changes, lignite and leaded petrol combustion, contributed to the shifts in Pb isotope ratios. Low-radiogenic petrol Pb ((206)pb/Pb-207 of 1.11) lead to lower (206)pb/Pb-207 in bark pockets over time. High-radiogenic lignite-derived Pb (Pb-206/Pb-207 of 1.18 to 1.19) was detected in areas affected by coal combustion rather than by traffic. (C) 2008 Elsevier B.V. All rights reserved.