Methylmercury Species Research Articles

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 CH(3)-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. CH(3)-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.

Measurement of Trace Elements in Marine Environmental Samples Using Solution ICPMS. Current and Future Applications

AbstractFor Abstract see ChemInform Abstract in Full Text.

Degradation of monomethylmercury chloride by hydroxyl radicals in simulated natural waters

The degradation of methylmercury chloride by hydroxyl radicals ( OH) has been investigated using nitrate photolysis from 285 to 800 nm with a 450 W Xenon lamp as the OH source. The identified products are Hg 2+, Hg 0, CHCl 3 and formaldehyde. The second-order rate constant at pH of 5 at room temperature was determined to be 9.83(+−0.66)×10 9 M −1 s −1using benzoic acid as the OH scavenger. The effects of chloride concentration and methylmercury speciation have also been investigated. A mechanism of the CH 3HgCl– OH reaction has been proposed. The calculated methylmercury degradation rates in natural waters using the above rate constant were comparable to the in situ photodegradation rates reported previously, indicating that degradation by •OH may be one of the important pathways of methylmercury degradation in sunlit surface waters.

Measurement of Trace Elements in Marine Environmental Samples using Solution ICPMS. Current and Future Applications

The strengths and weaknesses of using inductively coupled plasma mass spectrometer (ICPMS) measurements of samples in solution for marine environmental analyses using real world examples is discussed. ICPMS can detect nanogram per litre concentrations of trace elements but suffers from polyatomic interferences generated from the sample matrix. Most of the routine trace elements measured in marine biological tissue and sedimentdigests, with the notable exceptions of iron, chromium, vanadium, and selenium, are not subject to severe interferences. Low recoveries of trace elements from sediments are due to the inability of extraction acids to remove trace elements such as chromium and nickel from sediment matrices. The use of ICPMS offers the advantage that elements such as phosphorus, which previously required elaborate digestion procedures and a colorimetric determination, can be rapidly determined using nitric acid digestion alone. The use of flow injection coupled with ICPMS allows on-line preconcentration of trace metals and metalloids using chelation by ion-exchange resins or hydride generation and trapping as well as separation from matrix elements. Thus, the routine determination of trace elements and inorganic and methylated arsenic, antimony, mercury, and germanium species in open-ocean waters is possible. The coupling of HPLC and GC to ICPMS allows the measurement of metal and metalloid species in biological and sediment extracts. However, extraction of unaltered species from matrices presents a challenge. Many of the species found in the environmental samples are not known and analytical standards are not available. The concurrent use of HPLC-MS is needed to confirm these species.

Distribution of mercury, methyl mercury and organic sulphur species in soil, soil solution and stream of a boreal forest catchment

Concentrations of methyl mercury, CH3Hg (II), total mercury, Hgtot = CH3Hg (II) + Hg (II), and organic sulphur species were determined in soils, soil solutions and streams of a small (50 ha) boreal forest catchment in northern Sweden. The CH3Hg (II)/Hgtot ratio decreased from 1.2–17.2% in the peaty stream bank soils to 0.4–0.8% in mineral and peat soils 20 m away from the streams, indicating that conditions for net methylation of Hg (II) are most favourable in the riparian zone close to streams. Concentrations of CH3Hg (II) bound in soil and in soil solution were significantly, positively correlated to the concentration of Hgtot in soil solution. This, and the fact that the CH3Hg (II)/Hgtot ratio was higher in soil solution than in soil may indicate that Hg (II) in soil solution is more available for methylation processes than soil bound Hg (II). Reduced organic S functional groups (Org-SRED) in soil, soil extract and in samples of organic substances from streams were quantified using S K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Org-SRED, likely representing RSH, RSSH, RSR and RSSR functionalities, made up 50 to 78% of total S in all samples examined. Inorganic sulphide [e.g. FeS2 (s)] was only detected in one soil sample out of 10, and in none of the stream samples. Model calculations showed that under oxic conditions nearly 100% of Hg (II) and CH3Hg (II) were complexed by thiol groups (RSH) in the soil, soil solution and in the stream water. Concentrations of free CH3Hg+ and Hg2+ ions in soil solution and stream were on the order of 10−18 and 10−32M, respectively, at pH 5. For CH3Hg (II), inorganic bi-sulphide complexes may contribute to an overall solubility at concentrations of inorganic sulphides higher than 10−9M, whereas considerably higher concentrations of inorganic sulphides (lower redox-potential) are required to increase the solubility of Hg (II).

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 NaBH 4 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.

Methyl mercury uptake and associations with the induction of chromosomal aberrations in Chinese hamster ovary (CHO) cells

In order to evaluate possible health effects of environmental exposure of humans towards methyl mercury species, relevant exposure experiments using methyl mercury chloride in aqueous solution and Chinese hamster ovary (CHO) cells were performed. The solution was monitored for the presence of monomethyl, dimethyl and elemental mercury by several analytical techniques including chromatographic as well as atomic absorption and mass spectrometric methods. Methyl mercury induces structural chromosomal aberrations (CA) and sister chromatid exchanges (SCE) in CHO cells. At a concentration of methyl mercury in the culture medium of 1.0×10 −6 M where the frequencies of CA and SCE are significantly elevated, the intracellular concentration was 1.99×10 −16 mol/cell. Possible biochemical processes leading to the cytogenetic effects are discussed together with toxicological consequences, when humans (e.g. workers at waste deposits) are exposed to environmental concentrations of methyl mercury.

Determination of very low levels of dissolved mercury(II) and methylmercury in river waters by continuous flow with on-line UV decomposition and cold-vapor atomic fluorescence spectrometry after pre-concentration on a silica gel-2-mercaptobenzimidazol sorbent

A new, simple and sensitive method for the simultaneous determination of mercury(II) and methylmercury chloride at sub-ng l −1 levels in river waters is described. Inorganic and organic mercury were preconcentrated from fresh water samples simultaneously on a laboratory-made column containing 2-mercaptobenzimidazol loaded on silica gel and then quantitatively eluted with 0.05 M KCN solution and 2.0 M HCl to desorp inorganic and methylmercury species, respectively. After irradiation with an intensive UV source, MeHg + was decomposed and mercury vapours were generated from inorganic and organic mercury using an acidic SnCl 2 solution in a continuous flow system and were subsequently determined with a cold vapour atomic fluorescence (CV-AFS) spectrometer. Detection limits (3 σ) were 0.07 and 0.05 ng l −1 (as Hg) for mercury(II) chloride and methylmercury chloride, respectively. Relative standard deviations of method (%R.S.D.) were 8.8 and 10 for inorganic and organomercuric species in the river water, respectively. The analysis of real samples, taken from different rivers, showed that inorganic mercury levels ranged from 4.0±0.6 to 12±1 ng l −1 (as Hg and 95% confidence limit) and methylmercury levels at 0.2±0.02 ng l −1(as Hg).

Methylated mercury species in municipal waste landfill gas sampled in Florida, USA

Mercury-bearing material has been placed in municipal landfills from a wide array of sources including fluorescent lights, batteries, electrical switches, thermometers, and general waste. Despite its known volatility, persistence, and toxicity in the environment, the fate of mercury in landfills has not been widely studied. The nature of landfills designed to reduce waste through generation of methane by anaerobic bacteria suggests the possibility that these systems might also serve as bioreactors for the production of methylated mercury compounds. The toxicity of such species mandates the need to determine if they are emitted in municipal landfill gas (LFG). In a previous study, we had measured levels of total gaseous mercury (TGM) in LFG in the μg/m 3 range in two Florida landfills, and elevated levels of monomethyl mercury (MMM) were identified in LFG condensate, suggesting the possible existence of gaseous organic Hg compounds in LFG. In the current study, we measured TGM, Hg 0, and methylated mercury compounds directly in LFG from another Florida landfill. Again, TGM was in the μg/m 3 range, MMM was found in condensate, and this time we positively identified dimethyl mercury (DMM) in the LGF in the ng/m 3 range. These results identify landfills as a possible anthropogenic source of DMM emissions to air, and may help explain the reports of MMM in continental rainfall.

Oxidation of atomic mercury by hydroxyl radicals and photoinduced decomposition of methylmercury in the aqueous phase

The rate constant for Hg 0+ . OH, k Hg 0+ . OH =(2.4±0.3)×10 9 M −1 s −1 , in the aqueous phase was determined using a relative rate technique with methyl mercury as reference compound. The .OH initiated mercury reaction proceeds via the molecular Hg(I) radical which is oxidised to Hg(II) by dissolved O 2. The reaction can be of importance under certain atmospheric circumstances, such as when the aqueous phase capacity of forming OH radicals is significant and the gas phase concentration of ozone drops. The same end product, i.e. Hg(II) was observed from the photodegradation of methylmercury hydroxide. In this case, molecular Hg(I) radicals are again likely to be formed after photodegradation of the Hg–C bond with subsequent oxidation. A lifetime of 230 h of methylmercury at outdoor conditions was estimated due to this reaction. The action of .OH on methylmercury species also involves breaking of organometallic bonds and formation of Hg(II). Speciation of these reaction products from methylmercury is important for the estimation of biogeochemical cycling of mercury.

Use of Ultrasound in Sample Preparation for the Determination of Mercury Species by Cold-Vapor Atomic Absorption Spectrometry

Ultrasound was used for the intensification of sample preparation in the determination of different mercury species in brines and solutions of sodium chloride and common salt. Procedures were proposed for the determination of total mercury and inorganic, organic, and methyl mercury species.

Determination of methylmercury in fish tissue by gas chromatography with microwave-induced plasma atomic emission spectrometry after derivatization with sodium tetraphenylborate.

The detection of methylmercury species (MeHg) in fish tissue was investigated. Samples were digested with KOH-methanol and acidified prior to extraction with methylene chloride. MeHg was back-extracted from the organic phase into water. An aliquot of this aqueous solution (buffered to pH 5) was subjected to derivatization with sodium tetraphenylborate (NaBPh4) and then extracted with toluene. The organic phase containing MePhHg was injected into a gas chromatograph (GC) which is on-line with a microwave-induced plasma atomic emission spectrometer (MIP-AED). The quantification limit was about 0.6 microg/g and 0.1 microg/g of MeHg (as Hg) for 0.08 g of freeze-dried fish powder and 0.5 g of fresh samples, respectively. Two certified reference materials, CRM 464 (tuna fish) from Community Bureau of Reference-BCR and DORM-2 (dogfish muscle) from National Research Council Canada-NRC were selected for checking the accuracy of the method. This methodology was applied to the determination of MeHg in some kinds of fish from the Carmo river with alluvial gold recovery activities ("garimpos") in Mariana, Minas Gerais, Brazil.

Mercury speciation by capillary gas chromatography with radiofrequency hollow cathode glow discharge atomic emission detection

Hollow cathode (HC) glow discharge (GD) atomic emission spectrometry (AES) with a radiofrequency (rf) source was investigated as a detector in gas chromatography (GC) for elemental speciation of methylmercury, ethylmercury and inorganic mercury following a Grignard derivatisation reaction (butylmagnesium chloride). The HC design and the transfer line between the source and the GC column are described; in addition, the parameters governing the discharge (pressure, He flow rate, rf power) on the emission of the analytes were optimised. The analytical performance characteristics of this hyphenated technique were evaluated and compared with those of other more common plasmas used as atomic detectors in GC. The absolute detection limits were found to be 0.2, 0.2 and 0.3 pg for methylmercury, ethylmercury and inorganic mercury, respectively, with the variability being lower than 8% RSD at the 10 pg level. Finally, the accuracy of the proposed methodology was successfully tested by analysing two certified reference materials from the National Research Council of Canada (DORM-2 and DOLT-2).

Determination of methylmercury by solid-phase microextraction inductively coupled plasma mass spectrometry: a new sample introduction method for volatile metal species

Direct coupling of solid-phase microextraction (SPME) with inductively coupled plasma mass spectrometry (ICP-MS) is described for methylmercury speciation. A thermal desorption interface, consisting of a heated, glass-lined splitless-type GC injector, was placed directly at the base of the torch to minimize the length of transfer line. This arrangement provides for fast desorption and high sample introduction efficiency. Direct liquid immersion and headspace extraction of methylmercury was studied, including the effect of temperature and time on the extraction efficiency. For clean solutions, immersion sampling SPME provided good sensitivity that was linear over two orders of magnitude whereas headspace sampling showed 15% lower sensitivity, but a linear range of more than three orders of magnitude. The detection limit for headspace methylmercury sampling was 0.2 ng ml−1. Calibration by the method of additions using direct extraction revealed a severe matrix effect with biological tissue samples, diminishing the methylmercury response 70-fold, whereas that obtained by headspace extraction was statistically indistinguishable from signals generated using matrix free standards. Analytical results showed good agreement between certified and measured values for analysis of NRCC DORM-2, (Dogfish muscle) and DOLT-2 (Dogfish liver) reference materials.

Development of a fugacity/aquivalence model of mercury dynamics in lakes

A simple, mechanistic model of mercury (Hg) dynamics in a lake has been developed, based on the fugacity/aquivalence approach of Mackay (1991) and Mackay and Diamond (1989) and its extension to treat several interconverting chemical species (Diamond et al., 1992). The model considers the distribution of inorganic (HgII), elemental (Hg°) and methyl (MeHg) mercury species between dissolved and particle-sorbed phases, and fate and transport in a system consisting of a well-mixed water column and an active sediment layer. Hg can enter the lake from watershed runoff and by atmospheric deposition directly to the lake surface. Once in the lake, Hg exchanges between water and air, and water and sediments, and exits by sediment burial, advective flow and volatilization. The model was applied to a hypothetical drainage lake on the Canadian Shield. Model estimates of water and sediment concentrations compare well with measured values. The results suggest that the three Hg species experience significantly different fates and persistence, with overall Hg dynamics dominated by the fate of HgII (the predominant species). A sensitivity analysis illustrates the importance of physical/chemical properties and lake characteristics on the total amount and behavior of Hg in the lake.

Determination of methylmercury in fish and aqueous samples using solid-phase microextraction followed by gas chromatography-atomic fluorescence spectrometry

An analytical method is described for methylmercury determination in fish and aqueous samples using solid-phase microextraction (SPME) followed by gas chromatography–atomic fluorescence spectrometry (GC–AFS). The procedure involves aqueous-phase derivatization of methylmercury species with sodium tetraethylborate in a sample vial and subsequent extraction with a silica fiber coated with poly-­(dimethylsiloxane). The mercury derivatives are desorbed in the splitless injection port of a gas chromatograph and subsequently analyzed by GC–AFS. The headspace SPME procedure is used and parameters affecting the extraction, adsorption and desorption are evaluated. Results for methylmercury analysis in standard reference material (DORM-2) and fish samples are presented. © 1998 John Wiley & Sons, Ltd.

Determination of Concentration Profiles of Methyl Mercury Compounds in Surface Waters of Polar and other Remote Oceans by GC-AFD

The concentration of monomethyl mercury (MeHg+) and dimethyl mercury (Me2Hg) was determined in surface sea-water samples of the Antarctic and Arctic Ocean as well as of other remote areas (South Atlantic and South Pacific) during expeditions of the German research vessel “Polarstern”. A purge and trap/gas chromatographic system, equipped with an atomic fluorescence detector (AFD), was used. For the analysis of MeHg+ conversion into the volatile methylethyl mercury by reaction with tetraethyloborate prior to the purging process was carried out. The detection limit for both methylated mercury compounds was 5 pg Hg/L, which allowed their determination in most ocean water samples even in those of the Antarctic and Arctic Ocean. A north-south concentration profile in the Atlantic Ocean, covering a distance from 51°N to 58°S, was also examined, which resulted in the most extended set of data in the environment for these important heavy metal species. In anthropogenically influenced areas of the North Atlantic from 51°N to about 40°N concentrations of methylated mercury in the range of 100–3000 pg/L were found. The contents of these species were significantly lower in remote areas, represented by a range of <5 pg/L to 150 pg/L. Concentrations of the methylated mercury species were compared with those of substances often used as biomass indicators, e.g. chlorophyll-a and adenosine triphosphate. A positive correlation was found, in general, in remote areas between the contents of methylated mercury and these parameters for bioactivity, demonstrating the biogenic origin of MeHg+ and Me2Hg, respectively. The concentration of MeHg+ normally exceeded that of Me2Hg, except at locations with especially high bioactivities. This result indicates that Me2Hg may be the main primary biogenic product. Oceanographic conditions are very well reflected by concentration profiles of methylated mercury. For example, in biologically very active upwelling regions peak concentrations of Me2Hg and MeHg+ were found, whereas in parts of the Antarctic Ocean, totally covered by ice, the concentration of methylated mercury was determined to be below the detection limit.

Theoretical Study of the Photodecomposition of Methyl Hg Complexes

Methyl mercury, an important pollutant, decomposes photolytically when exposed to sunlight. Methyl mercury chloride has been shown to yield CH3 and HgCl radicals upon photodecomposition under UV irradiation. We have calculated spectral transition energies for a number of methylmercury species using quantum mechanical methods, specifically the Hartree−Fock method, the Moller−Plessett second order perturbation theory method (MP2), and the configuration interaction singles method using polarized double-ζ relativistic effective core potential basis sets. We find that singlet to triplet absorptions occur at lower energy than that of singlet to singlet absorptions, by about 2−3 eV. The calculated singlet to triplet (S−T) energy is much lower for 1-coordinate CH3Hg+ than for the 2-coordinate species CH3HgL, where L=CH3-, OH2, OH-, Cl-, or SH-. Of the 2-coordinate species studied, CH3HgOH2+ and CH3HgSH show the lowest energy S−T transitions, with calculated maxima just below 5.0 eV (at the MP2 level). They should...

Speciation and sorption of mercury in two macro-tidal estuaries

Mercury speciation and partition were determined in two macro-tidal estuaries, the Loire and the Seine estuaries (France) during several cruises covering various hydrological conditions. Additional measurements were performed in freshwaters in order to assess temporal variations of mercury inputs to the estuaries during an annual cycle. In freshwater, average total ‘dissolved’ (< 0.8 μm) mercury concentration [(HgT)D] was 4.1 ± 2.1 pM in the Loire and 11.5 ± 9.7 pM in the Seine. Mean particulate mercury concentration [(HgT)p] was 0.95 ± 0.63 nmol g−1 in the Loire and 5.4 ± 2.6 nmol g−1 in the Seine. The seasonal variation in the mercury concentrations in the two rivers are interpreted in terms of changes in the various water sources during flood events and variable contribution of colloidal materials. In the estuarine parts, (HgT)D concentrations generally varied from 2 to 6 pM in the Seine and from 1 to 3 pM in the Loire, while (HgT)P concentrations varied between 0.5 and 5 nmol g−1 in the Loire and between 2.5 and 10 nmol g−1 in the Seine. Because of its high distribution coefficient (log Kd = 5–6) and the high turbidity of these environments, mercury is mainly transported in particulate form in freshwaters as well as in mixing zones. Relationships between Kd and concentrations of suspended particles, dissolved and particulate organic carbon allow to describe the partition of mercury between solid and dissolved phases in terms of colloids, organic complexation in solution and sorption processes. Chlorocomplex formation does not play the major role in the speciation of Hg during the estuarine mixing. Organic associations, through sulphydryl groups, seems to be the dominant processes governing mercury distribution and partition in the two macro-tidal estuaries studied. Primary production appears to play an important role in the mercury dynamic. (HgT)P is correlated with the chlorophyll content of the particles in high flow regime of the Loire river, while elemental mercury (Hg0) was found to be related to the oxygen saturation rate in both estuaries. The production of Hg0 was sufficient to sustain a significant evasion flux to the atmosphere. Dimethylmercury was detected at fentomolar level during one cruise in the Baie de la Seine during an hypoxia episode. Highest monomethylmercury concentrations (up to 4% of the HgT) were associated with warmer and organic rich freshwater. Candidate sources for methylated mercury species are discussed. Both estuaries appear to be affected by local anthropogenic inputs. However, the Seine river is more deeply impacted by human activities. Watershed yields of the total Hg were calculated for the two drainage basins. The Seine yield (41 mmol km−2 a−1) is in the range of what is found in other urban areas, while for the Loire (9 mmol km−2 a−1) it is close to values found for agricultural watersheds. In spite of the anthropogenic inputs within the two estuaries, the riverine dissolved mercury inputs to the adjacent coastal waters (la Baie de la Seine and le Grand estuaire de la Loire) have been estimated to be half of the corresponding atmospheric depositions.

Speciation of Methyl- and Inorganic Mercury in Biological Tissues Using Ethylation and Gas Chromatography With Furnace Atomization Plasma Emission Spectrometric Detection

A sensitive and interference-free method for the quantification of inorganic and methylmercury species in biological tissues is presented using purge-and-trap injection–GC–AES. Samples were solubilized with tetramethylammonium hydroxide and the ionic species were purged from aqueous solution after ethylation with sodium tetraethylborate. The species were preconcentrated on Tenax-TA and thermally desorbed onto an isothermal (90 °C) GC column packed with 15% OV-3 on Chromasorb W. The separated species were eluted in He to a FAPES source for detection by AES at 253.6 nm. Absolute detection limits of 1 and 7 pg for inorganic and methylmercury, respectively, can be obtained, corresponding to concentration LODs of 0.2 and 1.4 ng g -1 , respectively, in solid tissue samples. Precision of determination is better than 10% RSD. The accuracy of the technique was validated by the analysis of National Research Council of Canada CRMs DORM-2, DOLT-2 and TORT-2, certified for mercury species content.