Quantification of Pollutant Lead in Forest Soils

Abstract

Fifteen podzolic forest soils in Norway covering sites with a wide range of atmospheric deposition rates were assayed for their contents of pollutant Pb. Samples from the Of, Oh, E, B, and C horizons were studied. Nitric acid soluble contents of Pb and the corresponding stable Pb isotope ratios were determined by sector field inductively coupled plasma–mass spectrometry (ICP–MS). On the basis of existing knowledge on 206 Pb/ 207 Pb ratios in atmospheric deposition over Norway across time, the percentage of the Pb supplied by air pollution was calculated for the various samples and soil horizons, assuming that the C horizon was undisturbed. More than 90% of O horizon Pb was from pollution, even at remote sites in the far north. Significant fractions of Pb were pollution‐derived also in the E and B horizons at most sites. In the south, more than half of the Pb derived from air pollution has now moved to the upper mineral horizons. Stable Pb isotope ratios are a very precise tool for revealing Pb pollution in terrestrial ecosystems. The present work suggests that similar studies should be done in other parts of the world to objectively assess the anthropogenic contribution to surface soil Pb.