Determination of lead concentrations and isotope ratios in recent snow samples from high alpine sites with a double focusing ICP-MS

A double focusing ICP-MS, equipped with a Micro Concentric Nebulizer, has been used to determine concentrations and isotopic ratios of lead in recent snow samples (1993-1996) from high alpine sites in Switzerland. Concentrations varied between 0.02 +/- 0.002 and 5.5 +/- 0.15 ng/g and are slightly lower than concentrations reported by Atteia [1], by Batifol et al. [2], and by Wagenbach et al, [3] for precipitation samples from similar remote sites in Europe. Since concentrations of lead in the fresh snow samples were mainly in the lower pg/g range, the method to determine the isotopic ratios Pb-207/Pb-206 and Pb-208/Pb-206 had to be optimized. They could finally be determined with an average standard error of 0.14% within 12 min and a total sample consumption of 0.8 mt. The average ratios Pb-207/Pb-206 and Pb-208/Pb-206 were 0.875 and 2.117, respectively. These values are comparable to isotopic compositions of lead in aerosols collected in Western Europe [4] and are less radiogenic than predicted by Grousset et al. [5]. Our data indicate that, although lead emissions from traffic have decreased largely during the last 10 years, the contribution from this source in modem snow is still detectable and seems to be equal to the lead input from other anthropogenic sources (e.g. waste incineration, industry).