Mercury speciation in the French seasonal snow cover

Snow samples have been collected in the French Alps in 1998, 1999 and 2000 in order to measure both total Hg (Hg-T) and reactive Hg (Hg-R). Concentrations of Hg-T were between 13 and 130 pg g(-1) and Hg-R concentrations were below the detection limit (similar to 0.8 pg g(-1)). Hg speciation in snow was evaluated on the basis of ionic complexation equilibrium with chloride, hydroxide, oxalate. The pH of the snow was found to be an important parameter for Hg speciation. For pH values near 3, HgC2O4 is predominant in snow samples except for snow strongly influenced by anthropogenic sources (in which case HgCl, predominates). When pH > 4, Hg(OH)(2) and HgOHCl are predominant. These latter pH values are observed for precipitation not influenced by anthropogenic sources but more by soil erosion, e.g. Saharan dusts. The knowledge of Hg-r speciation in snow is a key question for understanding the mechanisms of transformation of these complexes in snow after precipitation. (C) 2002 Elsevier Science B.V. All rights reserved.