Fabienne Séby

Chromium speciation in solid matrices and regulation: a review

In recent years, the extensive use of chromium in industrial processes has led to the promotion of several directives and recommendations by the European Union, that try to limit and regulate the presence of Cr(VI) in the environment and to protect industrial workers using chromium and end-users of manufactured products. As a consequence, new standard methods and analytical procedures have been published at the EU level for Cr(VI) determination in soil, sludge, sediment, and similar waste materials, workplace atmospheres, cement, packaging materials, industrially produced samples, and corrosion-protection layers on some components of vehicles and electrical and electronic equipment. The objective of this article is to summarize the different directives and recommendations and to critically review the currently existing standard methods and the methods published in the literature for chromium speciation in the above mentioned solid matrices, putting the emphasis on the different extraction procedures which have been developed for each matrix. Particular attention has been paid to Cr(III) and Cr(VI) inter-conversions that can occur during extraction and efforts to minimize these unwanted reactions. Although the use of NaOH-Na2CO3 solutions with hot plate extraction seems to be the more widespread procedure, species transformation can still occur and several studies suggest that speciated isotope-dilution mass spectrometry (SIDMS) could be a suitable tool for correction of these interconversions. Besides, recent studies have proved the role of Cr(III) in chromium toxicology. As a consequence, the authors suggest an update of standard methods in the near future.

Chromium speciation by hyphenation of high-performance liquid chromatography to inductively coupled plasma-mass spectrometry—study of the influence of interfering ions

This study presents the development of a speciation method for chromium redox species by HPLC-ICP-MS. Chromatographic separation is performed with CG5A-CS5A columns set (Dionex) containing both anionic and cationic groups to retain Cr(VI) and Cr(III), respectively, associated with a nitric acid elution. After optimisation, detection limits lower than 0.5 µg L−1 were obtained for both Cr species. This method is free from interferences possibly linked to chloride and organic or inorganic carbon on the two most abundant chromium isotopes (52Cr+ and 53Cr+). A modification of the chemistry of Cr(III) was, however, observed in the presence of hydrogencarbonate ions. In this medium, for trivalent chromium, three peaks instead of one are present on the chromatograms. This modification was attributed to the hydrolysis of Cr(III) that occurs at these pH values. The accuracy of the analytical procedure was verified by analysing a certified reference material (BCR-CRM 544) and spiked natural waters. The concentrations found for Cr(VI) were in good agreement with the certified and spiked values. Because of the high reactivity of Cr(III) in alkaline medium, recoveries were not completely quantitative.

Unsuspected diversity of arsenite-oxidizing bacteria as revealed by widespread distribution of the aoxB gene in prokaryotes.

ABSTRACT In this study, new strains were isolated from an environment with elevated arsenic levels, Sainte-Marie-aux-Mines (France), and the diversity of aoxB genes encoding the arsenite oxidase large subunit was investigated. The distribution of bacterial aoxB genes is wider than what was previously thought. AoxB subfamilies characterized by specific signatures were identified. An exhaustive analysis of AoxB sequences from this study and from public databases shows that horizontal gene transfer has likely played a role in the spreading of aoxB in prokaryotic communities.

Taxonomic and functional prokaryote diversity in mildly arsenic-contaminated sediments

Arsenic-resistant prokaryote diversity is far from being exhaustively explored. In this study, the arsenic-adapted prokaryotic community present in a moderately arsenic-contaminated site near Sainte-Marie-aux-Mines (France) was characterized, using metaproteomic and 16S rRNA-encoding gene amplification. High prokaryotic diversity was observed, with a majority of Proteobacteria, Acidobacteria and Bacteroidetes, and a large archaeal community comprising Euryarchaeaota and Thaumarchaeota. Metaproteomic analysis revealed that Proteobacteria, Planctomycetes and Cyanobacteria are among the active bacteria in this ecosystem. Taken together, these results highlight the unsuspected high diversity of the arsenic-adapted prokaryotic community, with some phyla never having been described in highly arsenic-exposed sites.

Determination of hexavalent chromium in cement by the use of HPLC-ICP-MS, FPLC-ETAAS, spectrophotometry and selective extraction techniques

Due to the high toxicity of hexavalent Cr, an European directive has recently been issued limiting the content of water-soluble Cr(VI) in cement to a maximal concentration of 2 mg kg−1. In order to fulfil the legislative requirements, it is often necessary to use reducing agents to lower the content of hexavalent Cr in cement. In the present work the abilities of HPLC-ICP-MS, FPLC-ETAAS, spectrophotometry and selective extraction procedure were estimated for the determination of Cr(VI) in aqueous cement extracts, containing high and low Cr(VI) concentrations. After comparison of the analytical performances of the different analytical methods used, water extracts of different cement samples were analysed. A good agreement was obtained for cement samples containing Cr(VI) concentration higher than 6 mg kg−1. Differences between techniques in general did not exceed 10%. With the exception of selective extraction all techniques applied are accurate (recoveries of spiked samples lay between 95–103%) and of adequate sensitivity. The MIBK extraction procedure exhibited limitations in cement samples that were treated with reducing agents due to the gel formation in the organic phase. Because of its accuracy, high sensitivity and the high speed of the analysis, the HPLC-ICP-MS procedure could be recommended as a technique of choice. However, FPLC-ETAAS and spectrophotometry may also be applied for the determination of Cr(VI) in cement samples and cement samples treated with reducing agents.

Arsenic in Marina Sediments from the Mediterranean Coast: Speciation in the Solid Phase and Occurrence of Thioarsenates

Arsenic speciation was determined in marina sediments of the French Mediterranean coast. The sediment from L′Estaque marina was highly impacted by both metallurgical activities and by the commercial port of Marseille, in contrast to the sediment from St. Mandrier marina that was less polluted. In the solid phases, As(III) was the dominant species in the L′Estaque sediment, whereas As(V) was the main form in the St. Mandrier sediment, with total As concentrations in the range 160–350 mg/kg and 17–20 mg/kg, respectively. In both sites, arsenic was the major trace element detected in interstitial water, its concentration reaching values higher than 1 mg/L in the L′Estaque sediment. Sulfate-reduction seemed to be more active in the L′Estaque site, probably because of the availability of easily biodegradable organic matter. This condition favored the formation of thioarsenates that were quantified here for the first time in a polluted marine sediment. Thioarsenates represented 69 ± 24% of total dissolved As in the 15–60 cm depth sediment layer. Our results suggest that bacterial activity may significantly contribute to increased arsenic solubility and mobility in harbor sediments, where crude oil input stimulates sulfate-reducers.

Optimisation of selective alkaline extraction for Cr(VI) determination in dairy and cereal products by HPIC-ICPMS using an experimental design.

This study presents the optimisation through an experimental design then the validation of a method to determine Cr(VI) in certain foodstuffs by high-performance ionic chromatography with inductively coupled plasma mass spectrometry. This method is free from interferences possibly associated with chloride and organic or inorganic carbon. Analytical performances assessed by the accuracy profile method were satisfactory in terms of linearity, specificity, sensitivity, accuracy, repeatability and intermediate precision. Limits of quantification ranged from 0.6μg.kg(-1) in dairy products to 0.8μg.kg(-1) in cereal products. The method was applied to the determination of Cr(VI) in dairy and cereal products from different brands and origins. Despite the methods very high sensitivity, Cr(VI) was not found in all the studied samples. This confirms the results of the most recent studies using an on-line speciation method, and invalidates older studies that found traces of Cr(VI) in food by using a less specific off-line speciation method.

Optimization and validation of the methods for the total mercury and methylmercury determination in breast milk

The objective of the work was to develop and validate methods for the total Hg and methylmercury (MeHg) in breast milk that could be further used to obtain first data on chemical contamination of French breast milk. For total Hg determination, the potential of two techniques, namely Advanced Mercury Analyzer (AMA) and ICP MS, was compared. For MeHg determination, ICP MS detection associated to a quantification by isotopic dilution was used and the potential of a preliminary separation by gas or liquid chromatography was evaluated and discussed. The optimization studies have shown that AMA for total Hg determination and HPLC - ID - ICP MS, after a preconcentration step by freeze-drying, for MeHg quantification were the most relevant methods to use for epidemiologic studies. The figures of merit for both methods were evaluated by means of accuracy profiles in terms of limits of quantification (1.82 and 1.35µg Hg/kg dry weight, corresponding to 0.22 and 0.16µg Hg/kg wet basis for total Hg and MeHg, respectively), repeatability (2-11% and 3-8% for total Hg and MeHg respectively), intermediate precision reproducibility (4-12% and 4-8% for total Hg and MeHg respectively) and trueness bias (-0.1-9% and -4-0% for total Hg and MeHg respectively). The methods were then applied to 180 breast milk samples. Total Hg concentrations ranged from <LD to 16.9µg Hg/kg wet basis (<LD to 142µg Hg/kg dry weight) and the MeHg contents from <LD to 0.43µg Hg/kg wet basis (<LD to 3.67µg Hg/kg dry weight).

Thiomonas sp. CB2 is able to degrade urea and promote toxic metal precipitation in acid mine drainage waters supplemented with urea.

The acid mine drainage (AMD) in Carnoulès (France) is characterized by the presence of toxic metals such as arsenic. Several bacterial strains belonging to the Thiomonas genus, which were isolated from this AMD, are able to withstand these conditions. Their genomes carry several genomic islands (GEIs), which are known to be potentially advantageous in some particular ecological niches. This study focused on the role of the “urea island” present in the Thiomonas CB2 strain, which carry the genes involved in urea degradation processes. First, genomic comparisons showed that the genome of Thiomonas sp. CB2, which is able to degrade urea, contains a urea genomic island which is incomplete in the genome of other strains showing no urease activity. The urease activity of Thiomonas sp. CB2 enabled this bacterium to maintain a neutral pH in cell cultures in vitro and prevented the occurrence of cell death during the growth of the bacterium in a chemically defined medium. In AMD water supplemented with urea, the degradation of urea promotes iron, aluminum and arsenic precipitation. Our data show that ureC was expressed in situ, which suggests that the ability to degrade urea may be expressed in some Thiomonas strains in AMD, and that this urease activity may contribute to their survival in contaminated environments.

Study of the presence of micro- and nanoparticles in drinks and foods by multiple analytical techniques

A variety of food and drink samples (n = 21) were analyzed to evaluate the presence of (nano-) particles in their composition. After assessment of the sample pre-treatment step, a fast screening analysis was performed for drinks by Dynamic Light Scattering showing particles from 10 to 300 nm that could correspond to organic or metallic NPs. Metallic NPs were identified in foods by Single-Particle mode Inductively Coupled Plasma Mass Spectrometry and Asymmetrical Flow Field-Flow Fractionation coupled to Multiangle Laser Light Scattering and Inductively-Coupled Plasma Mass Spectrometry. The determination of Ti, Si and Ag concentration in the initial food suspensions, after filtration and centrifugal ultrafiltration enabled to estimate the ionic and nanoparticles content. Si-containing particles can be present in cappuccino powder as large aggregates and Si- and Al-containing particles in hot chocolate. Ti-containing NPs (80-200 nm) were found in chewing gum and Ag NPs in silver pearls (50-150 nm) used for decoration pastry.