Atmospheric Lead Pollution History during Four Millennia (2000 BC to 2000 AD) in Sweden

This paper discusses the history of atmospheric lead pollution, the past geographic distribution of atmospheric lead deposition in Sweden, and the fate of the pollution lead in boreal forest soils. The paper is based on analyses of 206Pb/207Pb isotope ratios and lead concentrations in lake sediments, peat deposits and soil profiles from Sweden. The first signs of atmospheric lead pollution date back to 3500 to 4000 years ago. There was a small, but clear peak during the Greek-Roman period around 0 AD. About 1000 AD a major and unreversed increase occurred; varved lake sediments disclose pollution peaks at about 1200 AD and 1530 AD, which match peaks in metallurgy in Europe. With the Industrial Revolution atmospheric lead pollution increased, however, not as much as usually suggested, and not at all from what can be called background values. Lead pollution increased markedly after World War II, peaked about 1970, and will, if the present trend continues, soon be back to Medieval levels. The distribution of pre-industrial pollution was similar to the contemporary pattern with a strong south to north gradient, as a result of northward atmospheric transport from continental Europe and the British Isles. The cumulative load of pollution lead through time is 2 to 3 g m−2 in S Sweden, and of this load at least 50% was deposited prior to 1800 AD. In boreal forest soils, the main part of this pollution lead has accumulated in the B horizon. Present-day concentrations in the mor layer are up to 1000 times higher than in the pristine forest prior to pollution.