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

Ag, Au, Pt, Pd and Ph have been measured at various depth intervals of a 140 m snow/ice core electromechanically drilled at an altitude of 4250 m in the French-Italian Alps. The measurements were made by double focusing ICP-MS with micro concentric nebulisation. It provides the first time series for these metals for the last two centuries. Observed concentrations range from 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 18th century, no clear increase is observed for Au and Pt. For Pd, Rh and especially Ag, however, concentrations are higher in the last decades than in ancient ice. From a qualitative review of the different possible natural and anthropogenic sources, it appears that volcanoes, mining and smelting activities, industry and waste incinerators, could be significant sources of these metals in high-altitude Mont Blanc snow and ice. Pronounced seasonal variations 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 the other hand, then are no clear seasonal variations, which suggests that these two metals originate from distant sources. (C) 2000 Elsevier Science Ltd. All rights reserved.