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Lead (Pb) is one of the most heavily utilized metals in human history having been exploited by man over thousands of years for a variety of metallurgical, medicinal, and industrial purposes. The cumulative output of Pb from mining is estimated to be 260 million metric tonnes, and 85% of this has occurred over the last two centuries. Global annual production of Pb from mining is about 3 million tonnes.
Terrestrial ecosystems all over Norway have been contaminated moderately to strongly by lead and other trace elements from atmospheric deposition as a result of long-range atmospheric transport from other parts of Europe. Especially the southernmost part of Norway has been strongly affected. The baseline 206Pb/207Pb used for long-range atmospheric transport in the Oslo area is between 1.13-1.15 depending on when it was deposited.
With the aim of developing a method for mapping the accumulated content of anthropogenic Pb and how deep in the soil profile atmospherically deposited lead has penetrated, the concentration of Pb and the ratio between the isotopes 206Pb and 207Pb has been studied in podzolic soils at four locations with different geology, i.e. age and type of bedrock, in the Oslo area, Norway.
Soil profiles were sampled by digging pits down to 50-70 cm depth at four places with different bedrock located 20-30 km from downtown Oslo. Samples of humus were collected from a minimum of five sub-sites around each soil pit for analysis of anthropogenic lead isotope signal as reference.
The ratio 206Pb/207Pb is c. 1.12-1.15 in samples of humus and c. 1.17-1.21 in the uppermost centimetres of the soil profile. The ratio 206Pb/207Pb increases towards depth and converges towards geogenic background values that are characteristic for the lithology at each site.
Knowledge of the regional geochemical background levels and the isotopic composition of lead in soils and sediments can be used in distinguishing particulate material contributed by anthropogenic activity from chemical stratification of lead as function of soil weathering processes.
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