Sample treatment selection for routine mercury speciation in seafood by gas chromatography–atomic fluorescence spectroscopy

A general analytical strategy for mercury speciation in seafood samples has been proposed to increase sample throughput. This consists of the initial determination of total mercury content, and then mercury speciation using gas chromatography coupled to atomic fluorescence spectroscopy. The appropriate sample treatment for mercury speciation is selected between a method based on aqueous ethylation with sodium tetraethylborate (Approach A: a rapid methodology for samples with methylmercury concentrations between 150 and 2000 ng g^?1) and another one based on the determination of organomercury chlorides (Approach B: a much more time‐consuming methodology, applicable to samples with methylmercury at 1.2–200 ng g^?1). Both procedures have been used together for the analysis of bivalves and fish samples. Copyright © 2005 John Wiley & Sons, Ltd.     

Determination of mercury(II), methylmercury and ethylmercury in the ng/ml range with an electrochemical enzyme glucose probe

Hg(II), methylmercury and ethylmercury have been determined with an electrochemical glucose probe. Mercury and its compounds inhibit the enzyme invertase which, in presence of its substrate, sucrose, produces glucose. When invertase is in presence of mercury its activity decreases; this causes a decrease of glucose production, which is monitored by the glucose sensor and correlated to the concentration of mercury in solution. Parameters such as pH, enzyme concentration, substrate concentration, and reaction and incubation time were optimized. Results showed that mercury, methylmercury and ethylmercury can be detected directly in aqueous solution in the range 2–10 ng/ml.     

Biological and environmental reference materials from the National Institute for Environmental Studies (Japan)

Biological reference materials for elemental speciation were prepared at the National Institute for Environmental Studies. A new human hair reference material, prepared by cryogenic grinding using a ceramic disc mill, is in the process of certification for methyl-Hg and trace elements. Hijiki seaweed reference material was prepared for As speciation studies, primarily for use in the analysis of As(V). Scallop tissue reference material will be certified for arsenobetaine.     

Quantum chemical study of the reaction mechanism of the methylmercury cation with 2-mercapto-2-methyltetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium chloride in aqueous media

The detoxication properties of 2-mercapto-2-methyltetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium chloride (II) with respect to the methylmercury cation (I) in the presence of six water molecules have been studied using the density functional theory (DFT) method. Interaction between I and II leads to generation of the hydroxonium cation, which catalyzes the demethylation process. The elementary stages of two reaction routes have been localized, and their thermodynamic and kinetic characteristics have been determined.     

Chalcogen–mercury bond formation and disruption in model Rabenstein's reactions: A computational analysis

Methylmercury is a highly toxic compound and human exposure is mainly related to consumption of polluted fish and seafood. The inactivation of thiol-based enzymes, promoted by the strong affinity binding of electrophilic mercuric ions to thiol and selenol groups of proteins, is likely an important factor explaining its toxicity. A key role is played by the chemistry and reactivity of the mercury–chalcogens bond, particularly Hg S and Hg Se, which is the focus of this computational work (level of theory: (COSMO)-ZORA-BLYP-D3(BJ)/TZ2P). We analyze nine ligand-exchange model reactions (the so-called Rabenstein's reactions) involving an entering ligand (methylchalcogenolate) and a substrate (methylchalcogenolatemethylmercury). Trends in reaction and activation energies are discussed and a change in mechanism is reported for all cases when going from gas phase to water, that is, from a single-well potential energy surface (PES) to a canonical S_N2-like mechanism. The reasons accounting for the biochemically challenging and desired displacement of methylmercury from a seleno/thiol protein can be found already in these model reactions, as can be seen from the similarities of the ligand exchange reactions in solution in thermodynamics and kinetics.     

Inter‐laboratory validation of EPA method 3200 for mercury speciation analysis using prepared soil reference materials

Determinations of the concentration of individual mercury species from environmental samples have increased significantly over the past decade. The techniques used for the determination of mercury species in soils or sediments generally involve a series of analytical steps (extraction, separation, detection) that may all be prone to systematic errors. An inter‐laboratory validation study of the EPA draft method 3200 was conducted under the auspices of the United States Environmental Protection Agency on two specifically prepared soil matrices. The study was performed successfully by a limited number of participating laboratories. Evaluation of the data demonstrates that the method is more highly efficient for extracting the highly toxic methylmercury than inorganic mercury. The proposed method does not induce transformation of methylmercury to inorganic mercury. Copyright © 2004 John Wiley & Sons, Ltd.     

The determination of methylmercury in biological samples by HPLC coupled to ICP‐MS detection

The use of high‐performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP‐MS) for the determination of methylmercury (MeHg⁺) in fish tissue and hair samples is described. Analysis of these sample types is required when carrying out biomonitoring studies to determine human dietary exposure to this toxic mercurial compound. The developed method used a mobile phase containing an organic modifier and a sulfydryl compound (1:1 v/v methanol:water containing 0.01% v/v 2‐mercaptoethanol) to limit peak tailing and aid separation. The chromatographic separation was coupled to the ICP‐MS detector via a short piece of PEEK tubing, attached to the nebulizer. A cooled spraychamber and oxygen addition post‐nebulization were required to limit the solvent loading on the plasma and reduce carbon build‐up on the cones, respectively. The sample preparation procedure employed a drying step followed by digestion of the sample using tetramethylammonium hydroxide (TMAH) and heating in an open vessel microwave system. Two fish tissue certified reference materials (CRM), tuna fish CRM 463 and 464 (BCR, Brussels), a tuna fish proficiency test sample, IMEP‐20 (IRMM, Geel, Belgium) and a hair CRM NIES no. 13 (National Institute of Environmental Science, Japan), were used to evaluate the method. The recovery of MeHg⁺ for these four materials was between 83 and 100%, with precisions better than 6% for three separate extractions of the different materials. The limit of quantitation for MeHg⁺ using the developed protocol was 0.5 µg Hg g^?1. The stability of MeHg⁺ in the fish sample extracts was also assessed and losses of 14–16% were observed after storage of the extracts in a refrigerator at 5 °C, in high‐density polypropylene tubes, for 6 months. The developed protocol has been used previously with atmospheric pressure ionization mass spectrometry (API‐MS) to provide structural characterization and also with calibration via isotope dilution (IDMS) to provide high accuracy quantitation. Copyright © 2006 John Wiley & Sons, Ltd.     

In vitro effects of methylmercury on ascidian (Styela plicata) immunocyte responses

This study shows that high methylmercury concentrations are cytotoxic for Styela plicata hemocytes, whereas sublethal concentrations affect immunocyte responses. Moreover, hemocytes exposed to the xenobiotic present a significantly enhanced phenoloxidase activity as revealed in the hemocyte lysate supernatant compared with the control. Although the cytotoxic activity of S. plicata hemocytes toward rabbit erythrocytes is a PO‐dependent cell‐target reaction due to quinone products, it was significantly decreased by suitable methylmercury concentrations in the medium. The same xenobiotic concentrations decreased the hemocyte phagocytic activity toward yeast. In both the responses cell‐target contacts could be affected by methylmercury, whereas the releasing capacity appeared to be unchanged, as indicated by hemocyte PO‐release in the medium. Finally, changes in hemocyte shape and spreading capacity were shown. On the basis of the present results, Styela plicata hemocyte responses could be an additional immunotoxicology test using a microplate method that reveals cell morphological changes and spreading capacity. Copyright © 2007 John Wiley & Sons, Ltd.     

Complexation of CH3Hg+ with chloride,sulfate and carbonate in NaClO4: construction of thermodynamic models

The complexation of CH₃Hg⁺ with major ions present in sea and estuary waters (Cl^?, SO₄^2? and CO₃^2?) was studied potentiometrically in an NaClO₄ medium in the ionic strength range 0.1–3.0 mol dm^?3 at 25 °C. The potentiometric data, treated with non‐linear least squares computer programs, led us to establish the formation of the species CH₃HgCl in equilibrium with chloride, CH₃Hg(SO₄)^? species with sulfate and no complex with carbonate. The stoichiometric stability constants obtained at the different ionic strengths were correlated by means of the modified Bromley methodology (MBM) to determine the corresponding thermodynamic constants and interaction parameters. This study is the second of a series designed to simulate, using the MBM thermodynamic model, the behaviour of methylmercury in different conditions of sea and estuary waters. In the first study of the series, the hydrolysis equilibria of methylmercury in NaClO₄ ionic media were established. Copyright © 2002 John Wiley & Sons, Ltd.     

Transformations of mercury species in the presence of Elbe river bacteria

The influence of Elbe river bacteria isolated from suspended particulate matter (SPM) on dynamic species transformation of mercury was investigated. Experiments were carried out in the presence of bacteria (batch cultures) and in sterile tapwater as a control. For the methylation of inorganic mercury ions by bacteria several cofactors are under discussion. In this work, methylcobalamin, methyl iodide and S-adenosylmethionine were tested as biogenic methyl donors and trimethyl-lead chloride, trimethyltin chloride and dimethylarsenic acid as abiotic methyl donors. Transmethylation reactions as examples of abiotic methyl transfers have higher effectiveness in the formation of methylmercury (CH₃Hg⁺) than methylation with biogenic compounds. This result was observed in batch cultures as well as in sterile water. SPM-bacteria inhibit methyl transfer to mercury(II) ions. This is not only due to passive adsorption processes of mercury(II) to bacterial cell walls; methylmercury is also decomposed very rapidly by SPM-bacteria and is immobilized as mercury(II) by the cells.