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.     

Total reflection X-ray fluorescence mercury analysis after immobilization on quartz surfaces

Quartz reflectors are a common substrate for total reflection X-ray fluorescence (TXRF) analysis. Especially low masses of trace elements can be determined on these surfaces. In the present work, various complexing reagents were immobilized on the surface of quartz reflectors. The reflectors were immersed in mercury solutions and selective mercury collection took place. The effect of immersion time was examined and a few minutes were found adequate. The reflectors were analysed for mercury by TXRF. Different complexing reagents showed different collection capabilities; 4-(2-pyridazo-resorcinol) gave the best among them. The effect of various experimental parameters was examined like pH, interferences from other ions, etc. Mercury speciation was successfully tested by comparing inorganic mercury results with the methyl mercury ones. A very good selectivity for inorganic mercury was found. It was achieved very good linearity in the 1-500 ng mL⁻¹ mercury concentration range and the minimum detection limit was equal to 2.5 ng mL⁻¹.     

Stability of inorganic mercury and methylmercury on yeast-silica gel microcolumns: field sampling capabilities

The stability of methylmercury and inorganic mercury retained on yeast-silica gel microcolumns was established and compared with the stability of these species in solution. Yeast-silica gel columns with the retained analytes were stored for two months at three different temperatures: –20?°C, 4?°C and room temperature. At regular time intervals, both mercury species were eluted and quantified by cold vapor atomic absorption spectrometry (CVAAS). Methylmercury was found stable in the columns over the two-month period at the three different temperatures tested while the concentration of inorganic mercury decreased after one week’s storage even at –20?°C. These results are of great interest since the use of these microcolumns allows the preconcentration and storage of mercury species until analysis, thus saving laboratory space and avoiding the problems associated with maintaining species integrity in aqueous solution.     

Possible interferences of mercury sulfur compounds with ethylated and methylated mercury species using HPLC-ICP-MS

The HPLC-ICP-MS coupling technique is able to separate and detect methyl, ethyl and inorganic mercury isotopes specifically. An identification of ethyl mercury(+) is not possible when the widely used sodium tetraethylborate derivatisation method in combination with GC-AFS/AAS or ICP-MS techniques is performed because it contains ethyl groups.An unidentified compound with the same retention time as ethyl mercury was found in the HPLC chromatograms of industrial sewage samples and humic-rich soils of microcosm experiments after applying water vapour distillation. We also observed such unidentified peaks in samples of heavily contaminated sites in Eastern Germany, separated by HPLC fractionation only. In the experiments described, different mercury sulfur adducts were synthesised and tested for their retention times in the HPLC-ICP-MS system. It was found that the compound CH₃–S–Hg⁺ showed the same retention time as the ethyl mercury standard. It is therefore possible that ethyl mercury detected in chromatography by comparison of the retention time could also be due to an adduct of a sulfur compound and a mercury species. CH₃–S–Hg⁺ should be tested in other chromatographic mercury speciation methods for this effect.This work can also be regarded as a contribution to the discussion of artificially occurring methyl mercury in sediments during sample preparation.     

Simultaneous determination of inorganic mercury,methylmercury, and total mercury concentrations in cryogenic fresh-frozen and freeze-dried biological reference materials

Two speciated isotope dilution (SID) approaches consisting of a single-spike (SS) method and a double-spike (DS) method including a reaction/transformation model for the correction of inadvertent transformations affecting mercury species were compared in terms of accuracy, method performance, and robustness for the simultaneous determination of methylmercury (MeHg), inorganic mercury (iHg), and total mercury (HgT) concentrations in five biological Standard Reference Materials (SRMs). The SRMs consisted of oyster and mussel tissue materials displaying different mercury species concentration levels and different textural/matrix properties including freeze-dried (FD) materials (SRMs 1566b, 2976, and 2977) and cryogenically prepared and stored fresh-frozen (FF) materials (SRMs 1974a, 1974b). Each sample was spiked with (201)iHg (Oak Ridge National Laboratory, ORNL) and Me(202)Hg (Institute for Reference Materials and Measurements. IRMM-670) solutions and analyzed using alkaline microwave digestion, ethylation, and gas chromatography inductively coupled plasma mass spectrometry (GC/ICP-MS). The results obtained by the SS-SID method suggested that FF and FD materials are not always commutable for the simultaneous determination of iHg, MeHg, and HgT, due to potential transformation reactions resulting probably from the methodology and/or from the textural/matrix properties of the materials. These transformations can occasionally significantly affect mercury species concentration results obtained by SS-SID, depending on the species investigated and the materials considered. The results obtained by the DS-SID method indicated that the two classes of materials were commutable. The simultaneous and corrected concentrations of iHg, MeHg, and HgT obtained by this technique were not found to be statistically different form the certified and reference concentration together with their expanded uncertainty budgets for the five SRMs investigated, exemplifying the robustness, the accuracy, and the improved commutability of this method compared to SS-SID measurements.     

On-line separation for the speciation of mercury in natural waters by flow injection-cold vapour-atomic absorption spectrometry

Inorganic mercury and methylmercury are determined in natural waters by injecting the filtered samples onto a low cost commercial flow injection system in which an anion exchange microcolumn is inserted after the injection loop (FIA-IE). If hydrochloric acid is used as the carrier solution, the HgCl4(2-) species (inorganic mercury) will be retained by the anion exchanger while the CH3HgCI species (methylmercury) will flow through the resin with negligible retention. Four anion exchangers and seven elution agents were checked, in a batch mode, to search for the best conditions for optimal separation and elution of both species. Dowex M-41 and L-cysteine were finally selected. Mercury detection was performed by cold vapour-electrothermal atomic adsorption spectrometry (HG-ETAAS). Both systems were coupled to perform the continuous on-line separation/detection of both inorganic mercury and methylmercury species. Separation and detection conditions were optimized by two chemometric approaches: full factorial design and central composite design. A limit of detection of 0.4 microg L(-1) was obtained for both mercury species (RSD < 3.0% for 20 microg L(-1) inorganic and methylmercury solutions). The method was applied to mercury speciation in natural waters of the Nerbioi-lbaizabal estuary (Bilbao, North of Spain) and recoveries of more than 95% were obtained.     

Stability of inorganic mercury and methylmercury on yeast-silica gel microcolumns: field sampling capabilities

The stability of methylmercury and inorganic mercury retained on yeast-silica gel microcolumns was established and compared with the stability of these species in solution. Yeast-silica gel columns with the retained analytes were stored for two months at three different temperatures: -20 degrees C, 4 degrees C and room temperature. At regular time intervals, both mercury species were eluted and quantified by cold vapor atomic absorption spectrometry (CVAAS). Methylmercury was found stable in the columns over the two-month period at the three different temperatures tested while the concentration of inorganic mercury decreased after one week's storage even at -20 degrees C. These results are of great interest since the use of these microcolumns allows the preconcentration and storage of mercury species until analysis, thus saving laboratory space and avoiding the problems associated with maintaining species integrity in aqueous solution.     

Ionic alkyl-lead,tetra-alkyl-lead and total lead in fish from the Great Lakes

Fillets from a variety of fish species collected from Lakes Ontario, Superior and Erie, Canada, were examined for ionic alkyl-lead, tetra-alkyl-lead and total lead compounds. Diphenylthiocarbazone (dithizone)-derivatized extracts were collected at pH 8 and 9 for ionic alkyl-leads from enzymatically hydrolyzed samples. Butylated derivatives were formed prior to analysis by gas chromatography-atomic absorption spectrometry (GC AA). Tetra-alkyl-lead was extracted from the hydrolyzates with hexane. Most of the fillets contained low (<0.08–2 ng g^?1) levels of trimethyl-lead. Several samples contained triethyl-lead or tetraethyl-lead. Dimethyl-lead, diethyl-lead and tetramethyl-lead were detected by GC MS but were below the GC AA method detection limit of 0.06 ng g^?1, 0.09 ng g^?1 and 0.2 ng g^?1 respectively. Total lead levels were between <1.8 and 96.7 ng g^?1.     

Speciation analysis of mercury in sediments using ionic‐liquid‐based vortex‐assisted liquid–liquid microextraction combined with high‐performance liquid chromatography and cold vapor atomic fluorescence spectrometry

An improved novel method based on ionic liquid vortex‐assisted liquid–liquid microextraction has been developed for the extraction of methylmercury, ethylmercury and inorganic mercury in sediment samples prior to analysis by high‐performance liquid chromatography with cold vapor atomic fluorescence spectrometry. In this work, mercury species were firstly complexed with dithizone, and the complexes were extracted into 1‐hexyl‐3‐methylimidazolium hexafluorophosphate. Key factors that affect the extraction efficiency of mercury species, such as type and amount of ionic liquid and chelatants, extraction time, sample pH, salt effect and matrix effect were investigated. Under the optimum conditions, linearity was found in the concentration range from 0.1–70 ng/g. Limits of detection ranged from 0.037–0.061 ng/g. Reproducibility and recoveries were assessed by extracting a series of six independent sediment samples that were spiked with different concentration levels. Finally, the proposed method was successfully applied in analysis of real sediment samples. In this work, ionic liquids vortex‐assisted liquid–liquid microextraction was for the first time used for the extraction of mercury species in sediment samples. The proposed method was proved to be much simpler and more rapid, as well as more environmentally friendly and efficient compared with the previous methods.     

A ‘turn-on’ fluorescent probe that selectively responds to inorganic mercury species

A fluorescent probe selectively senses inorganic mercury in the turn-on mode through a mercury ion-promoted hydrolysis reaction that leads to a coumarin, among various other metal species except Au(III).     

Speciation of mercury in soil and sediment by selective solvent and acid extraction

In order to characterize the mercury hazard in soil, a sequential extraction scheme has been developed to classify mercury species based on their environmental mobility and/or toxicity for either routine lab analysis or on-site screening purposes. The alkyl mercury species and soluble inorganic species that contribute to the major portion of potential mercury toxicity in the soil are extracted by an acidic ethanol solution (2% HCl+10% ethanol solution) from soil matrices as "mobile and toxic" species. A High-Performance Liquid Chromatography (HPLC) system coupled with Inductively Coupled Plasma Mass Spectrometry (ICP-MS) detection has been developed to further resolve the species information into soluble inorganic species (Hg(2+)), methylmercury(II) (MeHg(+)) and ethylmercury(II) (EtHg(+)) species. Alternatively, these species can be separated into "soluble inorganic mercury" and "alkyl mercury" sub-categories by Solid-Phase Extraction (SPE). A custom Sulfydryl Cotton Fiber (SCF) material is used as the solid phase medium. Optimization of the SCF SPE technique is discussed. Combined with a direct mercury analyzer (DMA-80), the SCF SPE technique is a promising candidate for on-site screening purposes. Following the ethanol extraction, the inorganic mercury species remaining in soil are further divided into "semi-mobile" and "non-mobile" sub-categories by sequential acid extractions. The "semi-mobile" mercury species include mainly elemental mercury (Hg) and mercury-metal amalgams. The non-mobile mercury species mainly include mercuric sulfide (HgS) and mercurous chloride (Hg(2)Cl(2)).     

Sorption of mercury on chemically synthesized polyaniline

Summary Sorption of inorganic mercury (Hg²⁺) and methyl mercury, on chemically synthesized polyaniline, in 0.1-10N HCl solutions has been studied. Hg²⁺ is strongly sorbed at low acidities and the extent of sorption decreases with increase in acidity. The sorption of methyl mercury is very low in the HCl concentration range studied. Sorption of Hg²⁺ on polyaniline in 0.1-10N LiCl and H₂SO₄ solutions has also been studied. The analysis of the data indicates that the sorption of Hg²⁺ depends on the degree of protonation of polyaniline and the nature of mercury(II) chloride complexes in solution. X-ray photoelectron spectroscopy analysis (XPS) of polyaniline sorbed with mercury show that mercury is bound as Hg²⁺. Sorbed mercury is quantitatively eluted from polyaniline with 0.5N HNO₃. Polyaniline can be used for separation and pre-concentration of inorganic mercury from aqueous samples.     

Voltammetric quantification and speciation of mercury compounds

The use of a carbon paste electrode modified with a thiolic resin for the determination of inorganic mercury and organomercury compounds, present simultaneously in a sample, is described. The compounds are first preconcentrated at the electrode surface by means of a purely chemical reaction with the modifier on the electrode surface. The high affinity of the modifier for the mercury compounds ensures low limits of detection and determination. Differentiation between several mercury species is possible by control of the reduction potential applied to the working electrode. This selective reduction results in the formation of atomic mercury at the electrode surface which can be determined with a very high sensitivity by means of its re-oxidation wave in cyclic voltammetry. Optimization of the instrumental parameters and evidence for the reduction processes are discussed. Analysis of inorganic mercury in the presence of methylmercury, with a detection limit of 4 μg Hg 1⁻¹, and of methylmercury in the presence of inorganic mercury, with a detection limit of 2 μg Hg 1⁻¹, is described in detail. In both cases the preconcentration time is 6 min. Other organomercury species can also be quantified. Application of the method to environmental aquatic samples is discussed.     

Development of a mild mercaptoethanol extraction method for determination of mercury species in biological samples by HPLC–ICP-MS

A mild, efficient and convenient extraction method of using 2-mercaptoethanol contained extractant solution combined with an incubator shaker for determination of mercury species in biological samples by HPLC–ICP-MS has been developed. The effects of the concentration of 2-mercaptoethanol, the composition of the extractant solution and the shaking time on the efficiency of mercury extraction were evaluated. The optimization experiments indicated that the quantitative extraction of mercury species from biological samples could be achieved by using 0.1% (v/v) HCl, 0.1% (v/v) 2-mercapoethanol and 0.15% (m/v) KCl extractant solution in an incubator shaker for shaking overnight (about 12 h) at room temperature. The established method was validated by analysis of various biological certified reference materials, including NRCC DOLT-3 (dogfish liver), IAEA 436 (tuna fish), IAEA MA-B-3/TM (garfish filet), IAEA MA-M-2/TM (mussel tissue), GBW 08193 (bovine liver) and GBW 08572 (prawn). The analytical results of the reference materials were in good agreement with the certified or reference values of both methyl and total mercury, indicating that no distinguishable transformation between mercury species had occurred during the extraction and determination procedures. The limit of detection (LOD) for methyl (CH₃Hg⁺) and inorganic mercury (Hg²⁺) by the method are both as 0.2 μg L⁻¹. The relative standard deviation (R.S.D.s) for CH₃Hg⁺ and Hg²⁺ are 3.0% and 5.8%, respectively. The advantages of the developed extraction method are that (1) it is easy to operate in HPLC–ICP-MS for mercury species determination since the extracted solution can be directly injected into the HPLC column without pH adjustment and (2) the memory effect of mercury in the ICP-MS measurement system can be reduced.     

Speciation of mercury in human whole blood by capillary gas chromatography with a microwave-induced plasma emission detector system following complexometric extraction and butylation.

Methyl- and inorganic mercury were extracted from human whole blood samples, as their diethyldithiocarbamate complexes, into toluene and butylated by using a Grignard reagent. The mercury species were then separated by gas chromatography (on a 12 m non-polar DB-1 capillary column) and detected by a microwave-induced plasma atomic emission spectrometric (GC-MPD) system. The accuracy and precision of the proposed method were established by the analysis of Seronorm lyophilized human whole blood standards for methyl- and inorganic mercury. No statistical difference (t-test) between the sum of these two species determined by the GC-MPD based method and the recommended total mercury concentrations in the Seronorm samples was observed. Results for the determination of methyl- and inorganic mercury in 60 controls and 90 previously occupationally exposed (to inorganic mercury) workers are presented to illustrate the practical utility of the proposed method. No significantly elevated inorganic mercury concentrations between the two groups were evident.     

Phase transfer membrane supported liquid-liquid-liquid microextraction combined with large volume sample injection capillary electrophoresis-ultraviolet detection for the speciation of inorganic and organic mercury

In this paper, a novel sample pretreatment technique termed phase transfer based liquid-liquid-liquid microextraction (PT-LLLME) was proposed for the simultaneous extraction of inorganic and organic mercury species. In PT-LLLME, an intermediate solvent (acetonitrile) was added into the donor phase to improve the contacting between target mercury species and complexing reagent. Meanwhile, a membrane supported (MS)-LLLME unit was designed to realize the PT-LLLME procedure. By using nylon membrane as supporting carrier, larger than 50 μL of acceptor solution could be hung up. Following PT/MS-LLLME, the acceptor solutions were directly analyzed by large volume sample stacking capillary electrophoresis/ultraviolet detection (LVSS-CE/UV). Accordingly, a new method of PT/MS-LLLME combined with LVSS-CE/UV was developed for the simultaneous speciation of inorganic and organic mercury species. Parameters affecting the extraction efficiency of PT/MS-LLLME were investigated in details. Under the optimized conditions, enrichment factors (EFs) ranging from 160- to 478-fold were obtained for the extraction of target mercury species by PT/MS-LLLME. By combining PT/MS-LLLME with LVSS-CE/UV, EFs were magnified up to 12,138-fold and the limits of detection (at a signal-to-noise ratio of 3) were at sub ppb level. The established approach of PT/MS-LLLME-LVSS-CE/UV was successfully applied to simultaneous determination of inorganic and organic mercury species in biological samples and environmental water samples.     

Some aspects of speciation and reactivity of mercury in various matrices

Speciation of mercury compounds in environmental and biological samples requires different techniques and different approaches. This speciation is mandatory to explain the toxicity, the reactivity and the bioavailability of mercury. It is dominated by inorganic mercury species Hg(II) and Hg(0), and the organic mercury species CH₃Hg and (CH₃)₂Hg. In this paper, some aspects of mercury speciation are presented in terms of:- mercury reactivity (Hg(II) complexation and reduction),- mercury species distribution in the main compartments of the environment     

Alkylation of ionic mercury to methylmercury and dimethylmercury by methylcobalamin: Simultaneous determination by purge-and-trap GC in line with FTIR

A new approach was used to determine the reaction products of methylcobalamin and ionic mercury: purge-and-trap gas chromatography in line with Fourier transform infrared spectroscopy (PT GC/FTIR). This technique simultaneously and specifically determines the spectrum of dimethylmercury (DMeHg) and methylmercury produced by the reaction. No interference from other known organic mercury species could be detected. The method is different from others because it does not require solvent extraction of the organomercurials from aqueous solution, but relies on immediate volatilization from the reaction vessel by addition of 100 μl of 10 mM NaBH₄. The sample was purged with nitrogen for 10 min. The volatile species of mercury were trapped in a column at ?120°C, injected into the gas chromatograph and detected by FTIR. The efficiency of DMeHg and MeHg formation depended on different parameters: pH, temperature, reaction time, and the methylcobalamin/ionic mercury ratio. The initial reaction product was MeHg which was further transformed to DMeHg. The first methylation rate was two times faster than the second. MeHg formed first, reaching a maximum at higher temperatures (28°C and 37°C) and later decreasing as DMeHg formed. At lower temperatures (20°C) the rate of MeHg formation was slower, being similar to the formation rate of DMeHg. Different species of inorganic mercury such as HgSO₄, Hg(NO₃)₂, Hg(SCN)₂, HgCl₂ and Hgl₂ were used to study differences in methylation by methylcobalamin under standard conditions of acidity, temperature and cofactor Hg(II) ratio.     

Sequential quantification of methyl mercury in biological materials by selective reduction in the presence of mercury(II), using two gas–liquid separators

The present procedure is based on the sequential selective reduction of mercury(II) and methyl mercury using two gas–liquid separators in series. Cold vapor atomic absorption spectrometry was used for detection. Mercury(II) is reduced by a 0.01% m/v sodium tetrahydroborate solution and driven to the absorption cell in the first separator. The methyl mercury species is reduced by the same reductant but at a 0.3% m/v concentration, and in the presence of iron(III) chloride. Parameters such as argon flow rate, and the NaBH₄ and dithiophosphoric acid diacyl ester concentrations were optimized. At the optimized conditions, and using aqueous standards for calibration, the corresponding limits of detection (3σ_b, n=10) were 400 and 600 ng l⁻¹ for mercury(II) and methyl mercury, respectively. The sample throughput was 12 h⁻¹. The procedure was used for the determination of methyl mercury in dogfish liver and dogfish muscle certified reference materials, and good concordance between found and certified values was observed.     

Routine analysis of mercury species using commercially available instrumentation: chemometric optimisation of the instrumental variables

Mercury speciation analysis (inorganic mercury, Hg²⁺, methylmercury, CH₃Hg⁺ and dimethylmercury, (CH₃)₂Hg) by gas chromatography (GC) coupled to atomic emission spectroscopy with microwave induced plasma as excitation source (MIP-AES), after ethylation of the sample and extraction of the derivatised species into an organic phase, has been optimised using factorial design, analysis of variance and MultiSimplex techniques. Standard conditions were used in the derivatisation step with sodium tetraethylborate (NaB(C₂H₅)₄) and in the extraction step into hexane. Good separation of the species investigated and maximum sensitivity was achieved using an OV-1701 capillary column. The sensitivity was found to be maximum with an helium flow rate (make-up flow) of 100 ml min⁻¹. Procedures for a correct cleaning of glass and plastic ware, as well as for the purification of reagents used throughout the analytical process, are also suggested in order to avoid unacceptably high blank signals. The effect that ageing of stock solutions used in calibrations has on the artefact formation of CH₃Hg⁺ has been also investigated. Using the optimum conditions found, good quality calibration curves (R²>0.995) for the three mercury species were obtained. Absolute detection limits of 0.5, 3 and 15 pg of (CH₃)₂Hg, CH₃Hg⁺ and Hg²⁺, respectively, were estimated. The repeatability of the analysis was found to be better than 5% (n=5) in relative standard deviation (R.S.D.) units. The optimised procedure for the speciation of mercury in standard samples is the first step in the development of a method for routine analysis of mercury species in aquatic environmental samples.