Isotopic trends and background fluxes of atmospheric lead in northern Europe: Analyses of three ombrotrophic bogs from south Sweden

[1] Knowledge about the natural atmospheric background deposition rate of lead (Pb) prior to anthropogenic pollution is critical in the understanding of present-day pollution and for establishing realistic goals for the reduction of atmospheric Pb. We utilize stable Pb isotopes (Pb-206 and Pb-207) in radiocarbon-dated peat cores from three ombrotrophic bogs from south Sweden, to calculate fluxes and to survey atmospheric Pb trends prior 3500 BP ( the so far known onset of large-scale anthropogenic pollution). The estimated atmospheric Pb deposition rate was between 1 and 10 mug Pb m(2) yr(-1) between 5900 and 3700 calendar years BP, which is 100 to 1000 times lower than present-day deposition rates. The majority of the samples older than 3500 calendar years BP had Pb-206/Pb-207 ratios less than or equal to 1.20, which is significantly lower than unpolluted Swedish mineral soils (Pb-206/Pb-207 > 1.30), suggesting that even the natural atmospheric deposition of Pb was dominated by long-range transport, rather than local inputs from soil dust. Low Pb-206/Pb-207 ratios (1.16-1.18) of several samples indicate that this distant transport originated at least partly from early pollution sources. A possible climatic connection with the observed Pb deposition trends is suggested.