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Abstract: The isotopic composition of species-specific atmospheric mercury (Hg) was investigated in the coastal environment of Grand Bay, Mississippi, USA. Atmospheric mercury species (Hg0 (g), HgII (g) and Hg(p)) were collected individually, and analyzed for isotopic composition. Gaseous elemental Hg (Hg0 (g)) displayed δ202Hg ranging from −3.88‰ to −0.33‰. Aerosol Hg (Hg(p)) displayed intermediate δ202Hg ranging from −1.61‰ to −0.12‰, while reactive gaseous Hg (HgII (g)) displayed positive δ202Hg ranging from +0.51‰ to +1.61‰. Significant positive mass-independent fractionation (MIF) was observed in Hg(p) (∆199Hg=+0.36‰ to +1.36‰), while Hg0 (g) displayed negative MIF (∆199Hg=−0.41‰ to −0.03‰) and HgII (g) displayed intermediate MIF (∆199Hg=−0.28‰ to 0.18‰). Positive MIF of 199Hg and 201Hg measured in Hg(p) is consistent with significant in-aerosol photoreduction. Significant MIF of 200Hg was observed in all Hg species with Hg0 (g) displaying negative ∆200Hg values of −0.19‰ to −0.06‰ while HgII (g) and Hg(p) displayed positive ∆200Hg values of +0.06‰ to +0.28‰, which are similar to ∆200Hg values reported by Gratz et al. (2010). These results suggest that isotope tracing of each atmospheric Hg species may be feasible during important atmospheric processes such as wet and dry deposition. [Copyright &y& Elsevier]

The structure and function of a microbial community capable of biodegrading methyl- tert-butyl ether (MTBE) was characterized using compound-specific stable isotope analysis (CSIA), clone libraries and stable isotope probing of proteins (Protein-SIP). The enrichment culture (US3-M), which originated from a gasoline-impacted site in the United States, has been enriched on MTBE as the sole carbon source. The slope of isotopic enrichment factors (ℇC of −2.29±0.03‰; ℇH of −58±6‰) for carbon and hydrogen discrimination (Δδ2H/Δδ13C) was on average equal to Λ=24±2, a value closely related to the reaction mechanism of MTBE degradation in Methylibium petroleiphilum PM1. 16S rRNA gene libraries revealed sequences belonging to M. petroleiphilum PM1, Hydrogenophaga sp., Thiothrix unzii, Rhodobacter sp., Nocardiodes sp. and different Sphingomonadaceae bacteria. Protein-SIP analysis of the culture grown on 13C-MTBE as the only carbon source revealed that proteins related to members of the Comamonadaceae family, such as Delftia acidovorans, Acidovorax sp. or Comamonas sp., were not 13C-enriched, whereas proteins related to M. petroleiphilum PM1 showed an average incorporation of 94.5 atom%13C. These results indicate a key role for this species in the degradation of MTBE within the US3-M consortia. The combination of CSIA, molecular biology and Protein-SIP facilitated the analysis of an MTBE-degrading mixed culture from a functional and phylogenetic point of view. [ABSTRACT FROM AUTHOR]

Abstract: To characterize mercury (Hg) isotopes and isotopic fractionation in hydrothermal systems we analyzed fluid and precipitate samples from hot springs in the Yellowstone Plateau volcanic field and vent chimney samples from the Guaymas Basin sea-floor rift. These samples provide an initial indication of the variability in Hg isotopic composition among marine and continental hydrothermal systems that are controlled predominantly by mantle-derived magmas. Fluid samples from Ojo Caliente hot spring in Yellowstone range in δ202Hg from −1.02‰ to 0.58‰ (±0.11‰, 2SD) and solid precipitate samples from Guaymas Basin range in δ202Hg from −0.37‰ to −0.01‰ (±0.14‰, 2SD). Fluid samples from Ojo Caliente display mass-dependent fractionation (MDF) of Hg from the vent (δ202Hg=0.10‰±0.11‰, 2SD) to the end of the outflow channel (δ202Hg=0.58‰±0.11‰, 2SD) in conjunction with a decrease in Hg concentration from 46.6 pg/g to 20.0 pg/g. Although a small amount of Hg is lost from the fluids due to co-precipitation with siliceous sinter, we infer that the majority of the observed MDF and Hg loss from waters in Ojo Caliente is due to volatilization of Hg0 (aq) to Hg0 (g) and the preferential loss of Hg with a lower δ202Hg value to the atmosphere. A small amount of mass-independent fractionation (MIF) was observed in all samples from Ojo Caliente (Δ199Hg=0.13‰±10.06‰, 2SD) but no significant MIF was measured in the sea-floor rift samples from Guaymas Basin. This study demonstrates that several different hydrothermal processes fractionate Hg isotopes and that Hg isotopes may be used to better understand these processes. [Copyright &y& Elsevier]