Heavy metals in fresh snow collected at different altitudes in the Chamonix and Maurienne valleys, French Alps: initial results

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Abstract

The Chamonix and Maurienne valleys, French Alps, are major pathways for international truck and automobile traffic in Western Europe since they give access to the transalpine Mont Blanc and Frejus road tunnels. Moreover, the seasonal snow pack, which accumulates from autumn to spring in these two valleys, is a major contributor to fresh water resources for a large number of people, especially in large cities such as Geneva, Lyon and Grenoble. During winter 1998, we have collected a series of snow samples from two well-identified snowfall events at various altitudes ranging from 1150 to 3532 m on the sides of these two deep valleys. They were analysed for Li, B, Ti, V, Mn, Fe, Co, Cu, Zn, Mo, Pd, Ag, Cd, Sn, Sb, Ba, Pt, Au, Pb, Bi and U by double focusing inductively coupled plasma mass spectrometry with micro concentric nebulization (DF-ICP-MS-MCN). Ultraclean procedures were used for field sampling and laboratory analysis. The results show surprisingly low concentration values. With the exception of Li, B, Pd, Sn, Pt and Au, concentrations are found to decrease with increasing altitude. Crustal enrichment factors larger than ±10 times the mean crustal abundance are observed for Cu, Zn, Li, Mo, Pb, Ag, Bi, B, Sb, Sn, Cd, Au, Pt and Pd, strongly suggesting contributions from non-crustal sources for these metals, especially local and/or regional anthropogenic sources. Significant contributions are likely to originate from truck and automobile traffic, electrometallurgical and electrochemical industries and municipal incinerators. These data provide with a unique snapshot of the situation which prevailed in the two valleys before the disaster which occurred on 24 March 1999 in the tunnel of Mont Blanc, which resulted into a massive fall of the traffic in the Chamonix valley and a parallel rise in the traffic in the Maurienne valley.

Introduction

In the recent decades, there has been an increasing interest in heavy metals (Merian, 1991) in atmospheric precipitation and their possible environmental effects, see for instance Galloway et al. (1982), Munger and Eisenreich (1983), Barrie et al. (1987), Barrie and Schemenauer (1989), Muhlbaier Dasch and Wolff (1989), Atteia (1994), Poissant et al., 1994, Poissant et al., 1997 Riemann et al. (1996), Gregurek et al. (1999) and Simonetti et al. (2000). This is to a large extent because the atmospheric wet deposition pathway of numerous heavy metals potentially toxic to humans and other organisms is of major significance to many ecosystems.

Precipitation in deep alpine valleys represents a very interesting case because it is characterised by rather unique parameters. Local emissions of heavy metals to the atmosphere are indeed very significant as a consequence of extremely intense international and regional road traffic (with a large proportion of trucks), industry (especially electrometallurgy and electrochemistry which were set up in these valleys to take advantage of hydroelectricity) and various other sources such as refuse incineration. Moreover, there are very large differences in altitude, up to several kilometres, from the bottom of the valleys to the top of the surrounding mountains. Precipitation then occurs as snow during part of the year, especially for the mid or high altitude sides of the valleys. It means that there will be a time delay between heavy metals wet deposition in the seasonal snow cover from autumn to spring and heavy metals transfer to the local environment (soil, vegetation, rivers, etc.) when snow cover melting occurs. Also, these large differences in altitude result into characteristic vertical structures of the local atmosphere, with frequent thermal inversions during winter months and important vertical exchanges during the rest of the year (Van de Velde et al., 1998; Anquetin et al., 1999).

The Chamonix and Maurienne valleys (Fig. 1) are certainly two of the most interesting alpine valleys to be studied. They are indeed followed by the two main transalpine road links between France and Italy, which are extensively used for international truck traffic originating from all over Western Europe. These road links take advantage of the Mont Blanc and Frejus French–Italian road tunnels (Fig. 1) which were opened to traffic in 1965 and 1980, respectively. Another distinct feature is that they are extremely deep valleys: as an example, the difference in altitude between the bottom of the Chamonix valley and the summit of Mont Blanc which directly overlooks the valley is ∼3700 m. Finally, they are surrounded by large high altitude permanent cold snow and ice fields which have the potential to provide with time series of historical changes in heavy metals deposition since the Industrial Revolution (Van de Velde et al., 1998, Van de Velde et al., 1999, Van de Velde et al., 2000a, Van de Velde et al., 2000b; Heisterkamp et al., 1999; Rosman et al., 2000).

We present here initial data on heavy metals in snow collected at different altitudes ranging from 1150 to 3532 m in these two valleys. They were obtained by analysing fresh snow deposited during two snowfall events in February and March 1998. The analyses were performed by the ultrasensitive double focusing inductively coupled plasma mass spectrometry with micro concentric nebulization (DF-ICP-MS-MCN) technique.

Section snippets

Sampling sites and snowfall events

The snow samples from the Chamonix valley (Fig. 1) were collected on 13 March 1998, at eight locations whose altitude ranged from 1150 to 3532 m, (Fig. 2). The lowest sampling site at 1150 m altitude was located in Les Houches at the bottom of the valley. The 2310 m site was located near the Plan de l'Aiguille station of the Aiguille du Midi cable car. The six other sampling sites were along the Vallée Blanche ski trail which goes down from Aiguille du Midi (altitude: 3842 m) to Chamonix along the

Results and discussion

Heavy metals concentrations measured in the snow at the 14 sampling sites (eight in the Chamonix valley and six in the Maurienne valley) are given in Table 2, Table 3. For each site, the quoted values are the mean values for the two parallel samples collected at the site.

Conclusion

This work has provided with a first insight into the occurrence of numerous heavy metals in fresh snow from two well-identified snowfall events collected at different altitudes in two deep alpine valleys which are characterised by an intense international automobile and truck traffic linked with the presence of two major transalpine road tunnels of European importance. Quite unexpectedly, the snow was found to be extremely clean, with very low concentrations of many metals. These unexpected

Acknowledgements

This work was supported in France by the Agence de l'Environnement et de la Maı̂trise de l'Energie (Grant nb 9793011), the Ministry of the Environment (Grant nb 97036), Electricité de France, the Institut Universitaire de France, the University Joseph Fourier of Grenoble and the Institut National des Sciences de l'Univers. In Italy, it was performed in the framework of the Projects on “Environmental Contamination” and “Glaciology and Paleoclimatology” of the Italian Antarctic National Research

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