A global survey of reef fishes shows that the consequences of biodiversity loss are greater than previously anticipated as ecosystem functioning remained unsaturated with the addition of new species. Additionally, reefs worldwide, particularly those most diverse, are highly vulnerable to human impacts that are widespread and likely to worsen due to ongoing coastal overpopulation.

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This work reports the first results on the stable isotope fractionation of Hg during methylation by anaerobic bacteria under dark conditions. The GC-MC-ICPMS methodology employed is capable of simultaneously measuring the species-specific isotopic composition of different Hg species within the same sample. We have studied Hg isotopic fractionation caused by methylation of Hg(II) standard reference material NIST-3133 in the presence of the pure bacterial strain Desulfobulbus propionicus MUD10 (DSM 6523) under fermentative conditions. We have measured the isotopic composition of Hg(II) and monomethyl mercury (MMHg) in these cultures as a function of time and calculated delta-values for both species versus the starting material (NIST-3133) as a delta-zero standard. Two different strategies for the incubation were applied: single sampling cultures and a continuous sampling culture. The results obtained have shown that under the conditions employed in this work the methylation of Hg(II) causes mass-dependent fractionation of the Hg isotopes for both Hg(II) substrate and produced MMHg. Such a process occurred under the exponential growth of the bacteria which preferentially methylate the lighter isotopes of Hg. After 96 h for the continuous culture and 140 h for the single sampling cultures, we observed a change in the fractionation trend in the samples at a similar cell density value (ca. 6.0 x 10(7) cells mL(-1)) which suggests the increasing contribution of a simultaneous process balancing methylation extent such as demethylation. Assuming that Rayleigh type fractionation conditions are met before such suppression, we have obtained a alpha(202/198) fractionation factor of 1.0026 +/- 0.0004 for the single sampling cultures.

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This work presents the simultaneous online determination of the isotopic composition of different Hg species in a single sample by the hyphenation of gas chromatography (GC) with multicollector-inductively coupled plasma mass spectrometry (MC-ICPMS). With the use of commercially available instrumentation, precise and accurate species-specific Hg isotope delta values (per mil deviation of the Hg isotope ratio in the sample relative to a reference standard) have been obtained online from consecutive GC transient signals. The use of isothermal temperature programs to extend the elution of the Hg species, the proper selection of the peak integration window, as well as the preconcentration of real samples are critical to provide optimal counting statistics. Also, isotope ratio drift during transient signal elution was overcome by introducing a mixed Hg(II) and MeHg standard bracketing scheme and expressing all results using the delta-notation relative to SRM NIST-3133. Using the proposed methodology, we have obtained an external 2SD precision of 0.56 per thousand for delta (202)Hg that is more than 10 times smaller than the overall Hg stable isotope variation thus far observed in terrestrial samples. The measurement of species-specific Hg isotopic composition relative to SRM NIST-3133 has been validated versus two other analytical techniques, i.e., conventional nebulization (CN) of Hg(II) solution and cold vapor (CV) generation of Hg (0) vapor. A good agreement between the species-specific delta values obtained by the different techniques has been obtained in secondary fractionated reference standard (UM-Almaden) and environmental matrixes, i.e., BCR-CRM 464 (tuna fish) and IAEA-085 (human hair). The results show mass-dependent and mass-independent fractionation in environmental samples, i.e., mass-independent fractionation of odd isotopes (199)Hg and (201)Hg in tuna fish was observed. This methodology provides new possibilities for the future study of species-specific stable isotope geochemistry of Hg and other trace metals.

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The occurrence and speciation of volatile tin compounds (Sn) have been investigated in a contaminated area of the Arcachon Bay (SW France) and in the water column of the Scheldt (Belgium/Netherlands) and Gironde (SW France) estuaries. This paper describes the application of a multiisotope analytical method, using gas chromatography and inductively coupled plasma-mass spectrometry. Analytes were collected by cryogenic trapping of the gaseous species. This trapping has allowed us to probe volatile tin compounds by detecting both 118 Sn and 120 Sn isotopes. Volatile organic tin compounds have been determined in both sediment and water. They could result from both natural methylation and hydridization processes of inorganic tin (R n R′ 4-n Sn; R ) Me, R′ ) H, n ) 0-4) and from anthropogenic butyltin derivatives released from ship antifouling paintings which have accumulated in sediments (R n R′ 4-n Sn; R ) Bu, R′ ) H or Me, n ) 0-3). The most ubiquitous species were found to be the methylated forms of butyltin derivatives (Bu n SnMe 4-n , n ) 0-3). These results suggest that biological and/or chemical methylation mechanisms are likely to occur in sediments and to lead to remobilization of tin species into the water column and subsequently to the atmosphere. Finally, sediment-water and wateratmosphere fluxes have been calculated to assess the potential impact of these processes on the fate of organotin compounds in coastal environments.