Corinne Casiot

Bacterial immobilization and oxidation of arsenic in acid mine drainage (Carnoulès creek, France).

The acid waters (pH=2.73-3.37) originating from the Carnoulès mine tailings contain high dissolved concentrations of arsenic (1-3.5 mmol l(-1)) and iron (20-40 mmol l(-1)). At the outlet, arsenite predominates. During the first 30 m of downflow, 20-60% is removed by coprecipitation with Fe(III). This process results from bacterially mediated As- and Fe-oxidation. The precipitation rates in the creek depend on the oxygen concentration in spring water and are lower during the dry summer period when the anoxic character of the spring water inhibits the activity of oxidizing bacteria. Ex situ experiments show that the presence of bacteria-rich precipitates increases the As- and Fe-removal rates. Three strains of bacteria promoting the oxidation of As have been isolated, and two of them have the characteristics of Thiomonas ynys1. The third strain, which is not identified yet, also catalyzes the oxidation of Fe.

Sample preparation and HPLC separation approaches to speciation analysis of selenium in yeast by ICP-MS

Eight solid-liquid extraction procedures were evaluated for the recovery of selenium species from yeast. Speciation of Se in the extracts was characterized by different types of HPLC, including size-exclusion, anion-exchange and reversed-phase chromatography with ICP-MS detection. The results obtained depended critically on the sample preparation procedure used. Leaching with water and with methanol led only to 10-20% recoveries of Se, split into eight compounds, among which Se(IV) and selenomethionine could be identified. Leaching with pectinolytic enzymes released an additional 20% of selenomethionine. Leaching with sodium dodecyl sulfate solution allowed the solubilization of a selenoprotein that accounted for ca. 30% of the total Se present. Leaching with proteolytic enzymes led to recoveries of Se above 85%, the majority as selenomethionine. Hydrolysis of the yeast with tetramethylammonium hydroxide solubilized the sample completely but the Se species present were entirely degraded to selenomethionine and inorganic selenium. A sequential leaching procedure is proposed for the evaluation of selenium speciation in yeast without the need for a coupled technique.

Diversity of Microorganisms in Fe-As-Rich Acid Mine Drainage Waters of Carnoulès, France

ABSTRACT The acid waters (pH 2.7 to 3.4) originating from the Carnoulès mine tailings contain high concentrations of dissolved arsenic (80 to 350 mg · liter−1), iron (750 to 2,700 mg · liter−1), and sulfate (2,000 to 7,500 mg · liter−1). During the first 30 m of downflow in Reigous creek issuing from the mine tailings, 20 to 60% of the dissolved arsenic is removed by coprecipitation with Fe(III). The microbial communities along the creek have been characterized using terminal-restriction fragment length polymorphism (T-RFLP) and 16S rRNA gene library analyses. The results indicate a low bacterial diversity in comparison with unpolluted water. Eighty percent of the sequences obtained are related to sequences from uncultured, newly described organisms or recently associated with acid mine drainage. As expected owing to the water chemistry, the sequences recovered are mainly related to bacteria involved in the geochemical Fe and S cycles. Among them, sequences related to uncultured TrefC4 affiliated with Gallionella ferruginea, a neutrophilic Fe-oxidizing bacterium, are dominant. The description of the bacterial community structure and its dynamics lead to a better understanding of the natural remediation processes occurring at this site.

Metabolic diversity among main microorganisms inside an arsenic-rich ecosystem revealed by meta- and proteo-genomics

By their metabolic activities, microorganisms have a crucial role in the biogeochemical cycles of elements. The complete understanding of these processes requires, however, the deciphering of both the structure and the function, including synecologic interactions, of microbial communities. Using a metagenomic approach, we demonstrated here that an acid mine drainage highly contaminated with arsenic is dominated by seven bacterial strains whose genomes were reconstructed. Five of them represent yet uncultivated bacteria and include two strains belonging to a novel bacterial phylum present in some similar ecosystems, and which was named ‘Candidatus Fodinabacter communificans.’ Metaproteomic data unravelled several microbial capabilities expressed in situ, such as iron, sulfur and arsenic oxidation that are key mechanisms in biomineralization, or organic nutrient, amino acid and vitamin metabolism involved in synthrophic associations. A statistical analysis of genomic and proteomic data and reverse transcriptase–PCR experiments allowed us to build an integrated model of the metabolic interactions that may be of prime importance in the natural attenuation of such anthropized ecosystems.

An approach to the identification of selenium species in yeast extracts using pneumatically-assisted electrospray tandem mass spectrometry

An approach to the identification of unknown signals in selenium speciation analysis of yeast by reversed-phase chromatography with ICP-MS detection is described. The analytical strategy was based on: (i), heart-cutting of a Se-containing fraction in the reversed-phase chromatographic eluate followed by its lyophilization; (ii), pneumatically-assisted electrospray (ESI) MS and ESI tandem MS of the lyophilizate; and (iii) confirmation of the fragmentation pattern obtained using the sulfur analogue of the seleno compound that was expected to have been identified. The approach developed allowed the identification of Se–adenosylhomocysteine as the major selenium species in an extract of a selenized yeast sample.

Immobilization of Arsenite and Ferric Iron by Acidithiobacillus ferrooxidans and Its Relevance to Acid Mine Drainage

ABSTRACT Weathering of the As-rich pyrite-rich tailings of the abandoned mining site of Carnoulès (southeastern France) results in the formation of acid waters heavily loaded with arsenic. Dissolved arsenic present in the seepage waters precipitates within a few meters from the bottom of the tailing dam in the presence of microorganisms. An Acidithiobacillus ferrooxidans strain, referred to as CC1, was isolated from the effluents. This strain was able to remove arsenic from a defined synthetic medium only when grown on ferrous iron. This A. ferrooxidans strain did not oxidize arsenite to arsenate directly or indirectly. Strain CC1 precipitated arsenic unexpectedly as arsenite but not arsenate, with ferric iron produced by its energy metabolism. Furthermore, arsenite was almost not found adsorbed on jarosite but associated with a poorly ordered schwertmannite. Arsenate is known to efficiently precipitate with ferric iron and sulfate in the form of more or less ordered schwertmannite, depending on the sulfur-to-arsenic ratio. Our data demonstrate that the coprecipitation of arsenite with schwertmannite also appears as a potential mechanism of arsenite removal in heavily contaminated acid waters. The removal of arsenite by coprecipitation with ferric iron appears to be a common property of the A. ferrooxidans species, as such a feature was observed with one private and three collection strains, one of which was the type strain.

Optimization of the hyphenation between capillary zone electrophoresis and inductively coupled plasma mass spectrometry for the measurement of As-, Sb-, Se- and Te-species, applicable to soil extracts

The optimization of the hyphenation between capillary zone electrophoresis (CZE) and inductively coupled plasma mass spectrometry (ICP-MS) was studied for the simultaneous determination of metalloid species in the environment. Arsenic (arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid), selenium (selenite, selenate, selenomethionine, selenocystine), antimony (antimonate) and tellurium (tellurite, tellurate) species were simultaneously separated using a 75-μm i.d. fused silica capillary using either a chromate or a phosphate electrolyte. Different nebulizers were tested for introduction in the detector. A V-groove nebulizer (the Babington) and two concentric micronebulizers (the MCN-100 and the MicroMist) were studied in order to improve resolution, sensitivity and reproducibility. The optimization of CE-ICP-MS interface operating parameters is discussed for each nebulizer–interface combination, and special attention is given to the position of the capillary inside the nebulizer. Different nebulizer gas and liquid sheath flow rates were studied in detail and they hardly affect electrophoretic resolution and peak width. The best analytical performance characteristics were obtained with the MicroMist nebulizer. Detection limits with this nebulizer were found to range between 6 and 58 μg l−1 depending on the species investigated using pressure injection and below 1 μg l−1 for most of the species with electromigrative injection. Analysis of soil extracts showed that it was possible to carry out this technique on real samples.

Inorganic arsenic speciation at river basin scales : The Tinto and Odiel Rivers in the Iberian Pyrite Belt, SW Spain

The Tinto and Odiel rivers are heavily affected by acid mine drainage from mining areas in the Iberian Pyrite Belt. In this work we have conducted a study along these rivers where surface water samples have been collected. Field measurements, total dissolved metals and Fe and inorganic As speciation analysis were performed. The average total concentration of As in the Tinto river (1975 microg L(-1)) is larger than in the Odiel river (441 microg L(-1)); however, the mean concentration of As(III) is almost four times higher in the Odiel. In wet seasons the mean pH levels of both rivers (2.4 and 3.2 for the Tinto and Odiel, respectively) increase slightly and the amount of dissolved total arsenic tend to decrease, while the As(III)/(V) ratio strongly increase. Besides, the concentration of the reduced As species increase along the water course. As a result, As(III)/(V) ratio can be up to 100 times higher in the lower part of the basins. An estimation of the As(III) load transported by both rivers into the Atlantic Ocean has been performed, resulting in about 60 kg yr(-1) and 2.7t yr(-1) by the Tinto and Odiel rivers, respectively.

Persisting impact of historical mining activity to metal (Pb, Zn, Cd, Tl, Hg) and metalloid (As, Sb) enrichment in sediments of the Gardon River, Southern France

In this study, we assessed past and present influence of ancient mining activity on metal(loid) enrichment in sediments of a former mining watershed (Gardon River, SE France), that is now industrialized and urbanized. A sedimentary archive and current sediments were characterized combining geochemical analyses, zinc isotopic analyses and sequential extractions. The archive was used to establish local geochemical background and recorded (i) increasing enrichment factors (EFs) for Pb, Zn, Cd, Tl, Hg, As and Sb throughout the industrial era, (ii) a contamination peak in 1976 attributed to a tailings dam failure, and (iii) current levels in 2002 and 2011 similar to those of 1969, except for Sb and Hg, reflecting a persisting contamination pattern. Inter-element relationships and spatial distribution of EF values of current sediments throughout the watershed suggested that both ancient and current contamination had a common origin for Pb, Zn, Cd, Tl and As related to the exploitation of Pb/Zn mineralization while old Sb mines and coal extraction area were the main sources for Sb and Hg respectively. This prevailing mining origin was reflected for Zn by a relatively uniform isotopic composition at δ(66)Zn=0.23 ± 0.03‰, although slight decrease from 0.23‰ to 0.18‰ was recorded from upstream to downstream sites along the river course in relation with the contribution of the lighter δ(66)Zn signature (~0.08‰) of acid mine drainage impacted tributaries. Results from sequential extractions revealed that the potential mobility of the studied metal(loid)s varied in the order Sb<Tl≈As<Zn<Pb<Cd, with an increase of the mobile pool for Cd, Pb, Zn and to a lesser extent for As and Tl associated to increased enrichment. Altogether, these results tend to demonstrate that ancient mining activity still contributes to metal enrichment in the sediments of the Gardon River and that some of these metals may be mobilized toward the water compartment.

Predominance of Aqueous Tl(I) Species in the River System Downstream from the Abandoned Carnoulès Mine (Southern France)

Thallium concentration reached up to 534 μg L(-1) in the Reigous acid mine drainage downstream from the abandoned Pb-Zn Carnoulès mine (Southern France). It decreased to 5.44 μg L(-1) in the Amous River into which the Reigous creek flows. Tl(I) predominated (>98% of total dissolved Tl) over Tl(III), mainly in the form of Tl(+). Small amounts of Tl(III) evidenced in Reigous Creek might be in the form of aqueous TlCl(2)(+). The range of dissolved to particulate distribution coefficients log K(d) = 2.5 L kg(-1) to 4.6 L kg(-1) indicated low affinity of Tl for particles, mainly ferrihydrite, formed in the AMD-impacted watershed. The low retention of Tl(+) on ferrihydrite was demonstrated in sorption experiments, the best fit between experimental and modeled data being achieved for surface complexation constants log K(ads) = -2.67 for strong sites and log K(ads) = -3.76 for weak sites. This new set of constants allowed reasonable prediction of the concentrations of aqueous and particulate Tl resulting from the mixing of water from Reigous Creek and the Amous River water during laboratory experiments, together with those measured in the Amous River field study.