Pablo Rodriguez-Gonzalez

Determination of alkylated tin compounds in landfill leachates using isotopically enriched tin species with GC-ICP-MS detection

A method for the simultaneous determination of methylated, ethylated and butylated tin compounds in landfill leachates has been developed in this work. The assessment of the organotin compound composition has been achieved by the development of a specific GC-ICP-MS protocol adapted to these complex matrices. The analytical procedure consists in three major steps which have been carefully optimized, taking into account the variety of alkyltin compounds and the high organic content of the leachate matrix: nitric acid digestion under microwave, derivatization using sodium tetrapropylborate and chromatographic separation. Different quantification approaches are proposed for the determination of the alkyltin species in the leachates. In this way, isotope dilution analyses in the species-specific and species-unspecific spiking modes have been found to provide results in agreement with external and internal calibration approaches. A single analysis with an addition of three isotopically enriched butyltin species is found to be suitable for the routine quantitative and semi-quantitative determination of all occurring alkyltin species in landfill leachates. The different qualitative and quantitative GC-ICP-MS complementary approaches developed in this work allow the full organotin composition assessment of landfill leachates.

Isotopically-labelled compounds for validating organometallics speciation analysis

Abstract The possibilities of using isotopically-labelled species with GC-ICP-MS to validate speciation analysis of organometallic compounds in environmental samples are summarised. The analytical advantages of this unique way of quantification, based on isotope-ratio measurements in each separate species, are highlighted and compared with more conventional procedures. Particular emphasis is paid to validating published speciation procedures, which usually involve a large number of discrete steps, each a possible source of error. The preparation of isotopically-labelled butyltin species and its application to seawater and sediment organotin speciation quantitative analysis are reviewed. In addition, the impressive capability of the “multi-isotope-labelled multispecies” spikes to control every step in speciation, even the initial solid-liquid extraction of the species from a solid sample, is also addressed. Such an innovative strategy allows detection and correction for species degradation during this difficult step to follow the extraction process. Moreover, the use of such multi-isotope-labelled multispecies approaches opens the door to studies on reported extraction procedures in speciation work. This approach is shown to be extremely useful for both ensuring quantitative recoveries of the species being sought from the solid matrix and evaluating the extent of possible extraction-derived rearrangement reactions. The article reviews applications of this innovative tool to the study and validation of the reported solid-liquid extraction of butyltin species from a certified reference sediment (using different techniques, including mechanical shaking, microwave, ultrasonic and pressurized liquid extraction).

Comparison of different numerical approaches for multiple spiking species-specific isotope dilution analysis exemplified by the determination of butyltin species in sediments

An examination and comparison of all the mathematical approaches for multiple spiking species-specific isotope dilution analysis published so far in the literature is presented in this work with the determination of TBT and DBT in sediments. The basis of four different numerical approaches—Calculation of Stable Isotope Concentrations, Speciated Isotope Dilution Analysis, Species-Specific Isotope Dilution Analysis and Isotope Pattern Deconvolution—are explained and compared in terms of complexity, analytical figures of merit and specific advantages. The four methodologies have been found to provide exactly the same degradation-corrected concentrations for DBT and TBT in all samples even when different degradation extents are taking place. However, slight differences in the degradation factors have been obtained between two pairs of methods, being in all cases lower than the corresponding instrumental uncertainty of the values. The capability of extending the methodologies to a higher number of analytes by the use of additional enriched species as well as the specific advantages of the different methods is discussed. In this sense, it has been demonstrated that Calculation of Stable Isotope Concentrations and Isotope Pattern Deconvolution provide additional advantages such as the qualitative information on any non-spiked species present in the samples. In addition, using Isotope Pattern Deconvolution the performance of a new internal procedure for mass bias correction without the additional measurement of reference isotope ratios is presented.

An experimental approach to investigate mercury species transformations under redox oscillations in coastal sediments

This work describes a laboratory experiment designed to unravel mercury species reactivity in superficial coastal sediments oscillating between oxic and anoxic conditions. The experimental set-up has been applied to a sediment slurry from the Arcachon Bay (France) to follow the evolution of both naturally occurring (i.e. endogenous) and isotopically enriched added mercury species (i.e. exogenous, ¹⁹⁹IHg and ²⁰¹MMHg) at environmental levels. The transformation and partition between the different phases (aqueous, solid and gaseous) of the endogenous and exogenous mercury species (inorganic Hg (IHg), monomethyl Hg (MMHg), elemental Hg (Hg⁰) and dimethyl Hg (DMHg)) have been investigated by isotopic speciation methods throughout the experiment. The results demonstrate that the experimental approach is able to promote sediment redox oscillations and to simultaneously follow the biogeochemical fate of naturally occurring or added mercury species. Experimentally driven redox transition events were found to significantly enhance the aqueous Hg species concentrations, while the MMHg burden is not greatly affected. Indeed, during the anoxic-oxic transition, while aqueous endogenous IHg and MMHg exhibited a two-fold increase, aqueous exogenous IHg and MMHg increased 7 and 4 times, respectively. Transient increases of the net IHg methylation were recorded during the redox transitions with the largest increase of the MMHg contents (factor 1.8) observed during the oxic-anoxic transition. High resolution in situ redox experiments have not been performed up to now, therefore the developed experimental set-up provides novel insights in both the influence of redox conditions on Hg methylation/demethylation and adsorption/desorption processes and kinetics in superficial sediments.

Fate of mercury species in the coastal plume of the Adour River estuary (Bay of Biscay, SW France)

Because mercury (Hg) undergoes significant biogeochemical processes along the estuarine-coastal continuum, the objective of this work was to investigate the distribution and reactivity of methylmercury (MeHg), inorganic mercury (Hg(II)) and gaseous Hg (DGM) in plume waters of the Adour River estuary (Bay of Biscay). Vertical profiles, spatial and tidal variability of Hg species concentrations were evaluated during two campaigns (April 2007 and May 2010) characterized by significant plume extents over the coastal zone. Incubations with isotopically enriched tracers were performed on bulk and filtered waters under sunlight or dark conditions to investigate processes involved in Hg methylation, demethylation and reduction rates. Total Hg(II) concentrations were more dispersed in April 2007 (5.2 ± 4.9 pM) than in May 2010 (2.5 ± 1.1 pM) while total MeHg concentrations were similar for both seasons and averaged 0.13 ± 0.07 and 0.18 ± 0.11 pM, respectively. DGM concentrations were also similar between the two campaigns, averaging 0.26 ± 0.10 and 0.20 ± 0.09 pM, respectively. Methylation yields remained low within the estuarine plume (<0.01-0.4% day(-1)) while MeHg was efficiently demethylated via both biotic and abiotic pathways (2.3-55.3% day(-1)), mainly photo-induced. Hg reduction was also effective in these waters (0.3-43.5% day(-1)) and was occurring in both light and dark conditions. The results suggest that the plume is overall a sink for MeHg with integrated net demethylation rates, ranging from 2.0-3.7 g (Hg) d(-1), in the same range than the estimated MeHg inputs from the estuary (respectively, 0.9 and 3.5 g (Hg) d(-1)). The large evasion of DGM from the plume waters to the atmosphere (8.8-26.9 g (Hg) d(-1)) may also limit HgT inputs to coastal waters (33-69 g (Hg) d(-1)). These processes are thus considered to be most significant in controlling the fate of Hg transferred from the river to the coastal zone.

Application of a new focused microwave technology with species-specific isotope dilution analysis for the quantitative extraction of organometallic contaminants in solid environmental matrices

A new self-tuning single-mode-focused microwave technology has been evaluated in this work to perform the quantitative routine extraction of organometallic species from solid matrices of environmental interest. Species-specific isotope dilution analysis has been employed to better investigate the real influence of the microwave-assisted extractions on the final results. The advantages of such methodology in comparison with other established microwave units for the routine speciation analysis of organomercury and organotin compounds are discussed (such as the capability of using disposable glass vials, a self-tuning mode to provide an accurate control of the temperature and pressure inside of the vials, and the possibility of performing automated sequence of extractions with low sample size). The results obtained in this work demonstrated that such technology provides a fast and reliable quantitative extraction of the organometallic species in a wide range of extraction conditions even when the multi-elemental (Sn and Hg) species-specific determination is carried out.

Methylation and dealkykation of tin compounds by sulfate- and nitrate-reducing bacteria

In this study, axenic cultures of sulfate-reducing (SRB) and nitrate-reducing (NRB) bacteria were examined for their ability to methylate inorganic tin and to methylate or dealkylate butyltin compounds. Environmentally relevant concentrations of natural abundance tributyltin (TBT) and 116Sn-enriched inorganic tin were added to bacterial cultures to identify bacterial-mediated methylation and dealkylation reactions. The results show that none of the Desulfovibrio strains tested was able to induce any transformation process. In contrast, Desulfobulbus propionicus strain DSM-6523 degraded TBT either under sulfidogenic or non-sulfidogenic conditions. In addition, it was able to alkykate 116Sn-enriched inorganic tin leading to the formation of more toxic dimethyltin and trimethyltin. A similar capacity was observed for incubations of Pseudomonas but with a much greater dealkykation of TBT. As such, Pseudomonas sp. ADR42 degraded 61% of the initial TBT under aerobic conditions and 35% under nitrate-reducing conditions. This is the first work reporting a simultaneous TBT degradation and a methylation of both inorganic tin species and TBT dealkykation products by SRB and NRB under anoxic conditions. These reactions are environmentally relevant as they can control the mobility of these compounds in aquatic ecosystems; as well as their toxicity toward resident organisms.