A comparison of lead isotope ratios in the bark pockets and annual rings of two beech trees collected in Derbyshire and South Yorkshire, UK

ICP-MS analysis of the bark pockets and annual rings of two beech (Fagus sylvatica L.) trees collected from Longshaw, Derbyshire and Swinton, South Yorkshire in the UK recorded differences in the 206Pb/207Pb isotope ratio. In the Longshaw sample, the 206Pb/207Pb isotope ratio of the bark pockets (≈1914–1998, 78–260 μg g−1 Pb) declined from approximately 1.16 to 1.12, whilst the annual rings (1899–1998, 0.2–2.5 μg g−1 Pb) had a 206Pb/207Pb ratio of approximately 1.18. In the Swinton sample, the bark pockets (≈1919–1998, 7–78 μg g−1 Pb) declined from 1.15 to 1.11 and the annual rings (1899–1998, 0.2–0.5 μg g−1 Pb) from 1.18 to 1.15. The data implied that the bark pockets accumulated lead directly from the atmosphere through wet and dry deposition, whilst the annual rings accumulated lead from the soil via the roots. The bark pockets recorded a relative decline in the accumulation of lead from indigenous sources, such as lead smelting and coal combustion (1.17–1.19), and increase in imported sources such as the smelting of Australian ores (1.04) and leaded petrol usage (1.06–1.09). In contrast, the annual rings at Longshaw recorded ratios typical of indigenous lead, whilst the annual rings in Swinton recorded a relatively small decrease in 206Pb/207Pb reflecting leaded petrol usage. The decline in 206Pb/207Pb of the bark pockets was consistent with the historical decline in 206Pb/207Pb of atmospheric lead recorded in peat, lake sediments and archival herbage at other UK locations.