Distribution et role des composes soufres reduits volatils sur la speciation metallique

A sensitive, precise and rapid analytical method was elaborated to measure simultaneously 5 volatile reduced sulfur compounds (VRSC) ; hydrogen sulfide (H2S), carbonyl sulfide (OCS), methane thiol (MeSH), dimethyl sulfide (DMS), dimethyl disulfide (DMDS). The study of VRSC in the Bay of Quiberon highlights seasonal and interannual variations of concentrations in epibenthic zone. H2S analyzed near the sediment water interface (anoxic microzones), is more elevated in summer. The OCS distribution is consistent with a predominant photodegradation in winter and a sedimentary source in summer. The variations of MeSH, DMS and DMDS are correlated with the Dinophyceae abundance. In the Seine estuary, the absence of volatile H2S in the up estuary is explained by the presence of Cu2+ and Zn2+ (complexation). No significant interactions are observed between silver and OCS, MeSH, DMS. The distribution of MeSH, DMS and DMDS is linked to the phytoplanktonic abundance whereas the OCS's is governed by the organic sulfur compounds photodegradation and the sedimentary diffusion. In a phytoplanktonic culture submitted to increasing silver concentrations, the H2S concentration not seem to be influenced by the metal ions. The DMS degradation may be explained the increase of MeSH and DMDS concentrations. The OCS analyzed may be produced by the degradation of biogenic (phytoplankton) sulfur compounds.