HR: 08:45h
AN: B21C-04    [Abstracts]
TI: Ocean to Continent Transfer of Atmospheric Se: Emission, Sources and Fate as Revealed by Epiphytic Lichens
AU: Wen, H
EM: hjwen@crpg.cnrs-nancy.fr
AF: CRPG-CNRS, 15, rue Notre Dame des Pauvres, Vandoeuvre-lŠs-Nancy, 54501 France
AU: Wen, H
EM: hjwen@crpg.cnrs-nancy.fr
AF: Chinese Academy of Science, 73 road Guanshui, Guiyang, 550002 China
AU: * Carignan, J
EM: carignan@crpg.cnrs-nancy.fr
AF: CRPG-CNRS, 15, rue Notre Dame des Pauvres, Vandoeuvre-lŠs-Nancy, 54501 France
AB: Because of the very narrow margin between nutritionally optimal and potentially toxic dietary exposures for animals and humans, selenium sources and fate in the environment is an important question. The major sources of atmospheric Se include diverse anthropogenic activities, natural emission of marine biogenic Se and punctual volcanic contributions. Lichens have been used to document elemental atmospheric deposition, including that of volatile elements such as Se, Hg, Sb, As, and to evaluate the natural and anthropogenic input in the atmosphere. Here we report the Cl and Se contents in lichens and various relationships for estimating atmospheric Se sources. Samples were collected in coastal and inland areas from United States (west coast), Canada (west coast and Hudson Bay) and France (west coast). Se and Cl concentrations in samples from coastal areas are well correlated to each other, suggesting the two elements would originate from the same source. Cl is mainly derived from marine sources as sea salts generated from the sea spray. Se is also naturally emitted to the atmosphere from the seawater as methylated Se compounds such as DMSe, DMDSe and MeSeH. Adsorption of cations on negatively charged organic films will probably not be effective for Se because it mainly occurs as anionic forms in seawater. Rather, volatile methylated Se compounds are directly released at the sea surface and later adsorbed on atmospheric particles, leading to Se enrichment relative to Cl and related to the gas-to-particle partitioning. This emission process would explain the fact that Se/Cl ratio measured in "coastal" lichens is higher than that of the bulk seawater by about 5 orders of magnitude. This ratio also seems geographically dependant. For similar Cl concentrations, lichens from southern Hudson Bay (Canada) have a higher Se/Cl ratio than that measured in lichens from California (USA); the lichens from France being intermediate. We suppose that this difference might be the result of various plankton productivities leading to methylated Se compounds. In more continental areas, the Se/Cl ratio increases dramatically along with the decrease of Cl concentrations. This may be explained either by 1) anthropogenic Se input, or 2) an atmospheric residence time for the volatile methylated Se compounds higher than that for Cl. In general, the "continental" samples do not show good relationships between Se and other metal (Pb, Cu, In.) contents, even for lichens collected in the vicinity of smelters or close to urban areas. Our results suggest that the marine biogenic Se source is a major contributor to atmospheric Se.
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0330 Geochemical cycles (1030)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0461 Metals
SC: Biogeosciences [B]
MN: Fall Meeting 2005