Changes in the occurrence of silver, gold, platinum, palladium and rhodiumin Mont Blanc ice and snow since the 18th century

Ag, Au, Pt, Pd and Ph have been measured at various depth intervals of a 14 0 m snow/ice core electromechanically drilled at an altitude of 4250 m in t he French-Italian Alps. The measurements were made by double focusing ICP-M S with micro concentric nebulisation. It provides the first time series for these metals for the last two centuries. Observed concentrations range fro m 0.2 to 12 pg g(-1) for Ag; 0.07-0.35 pg g(-1) for Au, 0.08-0.62 pg g(-1) for Pt, 0.5-10 pg g(-1) for Pd and 0.01-0.39 pg g(-1) for Ph. Since the 18t h century, no clear increase is observed for Au and Pt. For Pd, Rh and espe cially Ag, however, concentrations are higher in the last decades than in a ncient ice. From a qualitative review of the different possible natural and anthropogenic sources, it appears that volcanoes, mining and smelting acti vities, industry and waste incinerators, could be significant sources of th ese metals in high-altitude Mont Blanc snow and ice. Pronounced seasonal va riations in the concentrations of Pd, Ph and especially Ag are observed in ice dating from the 1960s. They are largely due to changes in the vertical structure of the regional troposphere during the year. For Au and Pt, on th e other hand, then are no clear seasonal variations, which suggests that th ese two metals originate from distant sources. (C) 2000 Elsevier Science Lt d. All rights reserved.