Behaviour of potentially toxic elements (PTEs) and Pb isotopes in North-Trøndelag forest soil

Analysis of soil C and O horizon samples in a recent regional geochemical survey in central Norway (752 sample sites, 25,000 km2), identified a strong enrichment of several PTEs in the O horizon. Of 53 elements analysed in... [ view full abstract ]

Analysis of soil C and O horizon samples in a recent regional geochemical survey in central Norway (752 sample sites, 25,000 km2), identified a strong enrichment of several PTEs in the O horizon. Of 53 elements analysed in both materials, Cd concentrations are, on average, 17 times higher in the O horizon than in the C horizon and other such as PTEs Ag (11-fold), Hg (10-fold), Sb (8-fold), Pb (4-fold) and Sn (2-fold) are all enriched relative to the C horizon. In addition to element concentrations the Pb isotopes 206Pb, 207Pb and 208Pb were also determined.

Geochemical maps do not reflect an impact from local or distant anthropogenic contamination sources in the O horizon soil samples – neither for the PTEs nor for the Pb isotopes. The higher concentrations of PTEs in the O horizon and the isotopic composition of the O horizon soil are the result of the interaction of the underlying geology, vegetation, and climatic effects (weathering). Based on the general accordance with existing data from earlier surveys in other parts of northern Europe, the presence of a location-independent, superordinate natural trend towards enrichment of these elements in the O horizon relative to the C horizon soil is indicated. The Pb isotopes show a general shift towards lower 206Pb/207Pb ratios at surface when compared to values determined in the underlying soil C horizon. At the regional scale surface soil chemistry and isotopic composition is still dominated by natural sources and processes.