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 μg g−1) reflected air pollution in the city of Prague. The lowest Pb content (0.3–2.6 μg g−1) was found at the Kosetice EMEP “background pollution“ site. Changes in 206Pb/207Pb and 208Pb/206Pb isotope ratios were in agreement with operation times of the Czech main anthropogenic Pb sources. Shortly after the Second World War, the 206Pb/207Pb isotope ratio in bark pockets decreased from 1.17 to 1.14 and the 208Pb/206Pb 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 (206Pb/207Pb of 1.11) lead to lower 206Pb/207Pb in bark pockets over time. High-radiogenic lignite-derived Pb (206Pb/207Pb of 1.18 to 1.19) was detected in areas affected by coal combustion rather than by traffic.