Concentrations Of Mercury Species Research Articles

Salmon‐derived mercury and nutrients in a Lake Ontario spawning stream

We tested the hypothesis that concentrations of mercury species (Hg) and nutrients (NH4+, NO3−, P, and dissolved organic carbon) in abiotic and biotic components would be altered by the decomposition of salmon carcasses in streams. We investigated a tributary stream of Lake Ontario receiving spawning runs of Chinook salmon (Oncorhyncus tshawytscha) for 2 yr with contrasting bear activity. Stations with high carcass densities had significantly higher levels of aqueous total Hg, methylmercury (MeHg), particulate Hg, and nutrients than did stations with lower carcass densities. Hg levels in aquatic and terrestrial invertebrates feeding on carcasses increased by up to 25‐fold. In 2001, a bear removed most carcasses at the downstream station, and aqueous Hg and nutrient concentrations were significantly lower than during the preceding year, when no bear was active at that station. A preliminary budget for this stream shows that (1) salmon carcasses can be an important source of Hg and nutrients to aquatic and terrestrial food webs, and (2) terrestrial invertebrates and vertebrates can be important water‐to‐land vectors of Hg.

Application of multiple stable mercury isotopes to determine the adsorption and desorption dynamics of Hg(II) and MeHg to sediments

Enriched stable isotopes were added to sediment suspensions of a freshwater lake to study the kinetics of Hg(II) and methylmercury partitioning between the dissolved and solid phase. 200Hg(II) and Me 199Hg were spiked to lake sediment suspensions and concentrations of dissolved and solid phase mercury species were measured in regular intervals over a 2-day period. Equilibrium concentrations were established for the added 200Hg(II) and Me 199Hg within the first 60 min with average partitioning constants (log K d) for total Hg and methylmercury reaching values of 4.3 and 3.9, respectively. Desorption was instantaneous (<30 min). No secondary adsorption and desorption was observed during the duration of the experiment. Spiking with different concentrations of mercury species revealed and inhomogeneous distribution of binding sites. The adsorption process was described using the Freundlich isotherm showing a reduced sorption capacity at lower equilibrium concentrations, suggesting a limited capacity of strong binding sites. Me 200Hg formation was observed during the experiment and as much as 3.5% of the added 200Hg(II) tracer was methylated. The results suggest that the vast majority of dissolved mercury species quickly equilibrate with the solid phase.

Dynamics of mercury species in surface sediments of a macrotidal estuarine–coastal system (Adour River, Bay of Biscay)

Estuarine and coastal surface sediments from the Adour estuary and adjacent coastal area (South Bay of Biscay) have been investigated to establish mercury species variability in a macrotidal system submitted to contrasted seasonal river discharges and downstream urbanisation. Surface sediments were sampled during three campaigns in the major sediment deposits of the Adour estuary and at selected discharge points. Concentrations of Hg 2+ and MeHg + in Adour estuarine sediments average 1600 and 1.3 pmol g −1, and range from <2 to 7300 pmol g −1 and from <0.5 to 8.0 pmol g −1, respectively. The concentrations of inorganic ionic mercury (Hg 2+) and monomethylmercury (MeHg +) in the surface sediments display large seasonal variation, being one order of magnitude higher in June 2001 for Hg 2+ and in October 2000 for MeHg +. The results show that Hg 2+ can be accumulated in the estuarine sediments after seasonal river inputs and both remobilised and methylated during dry period. Mercury species concentrations in coastal sediments collected in June 2001 assessed the impact of estuarine inputs on the nearby coastal area. Except direct anthropogenic discharge points, the variability and transfer of Hg 2+ and MeHg + in surface sediments of the whole estuarine–coastal macrotidal system can be depicted by simple geochemical parameters of the bulk sediments, such as grain size distribution, organic carbon and total sulphur.

Mercury transformations and exchanges in a high turbidity estuary:: The role of organic matter and amorphous oxyhydroxides

The speciation and partition of mercury in a macrotidal estuary (Seine estuary, France) was studied in order to explore the role of the high turbidity zone (HTZ) in mercury transfer to the adjacent coastal waters. Water and particles were analyzed to determine the concentrations of various mercury species, including monomethylmercury and the inorganic fraction. The exchangeable particulate mercury, which varies with salinity, and the mercury fraction associated with the amorphous oxyhydroxides were evaluated. The distribution of dissolved mercury species during early mixing suggests non-conservative behavior of organically bound mercury at the head of the estuary. Mercury in the particles covaried positively with suspended particulate matter concentrations up to a threshold, which constitutes the typical mercury load of particles and deposited sediments of the HTZ. This distribution pattern is well explained by a dilution model: a slowly settling, low metal population of particle, characterized by relatively invariant turbidity, becomes admixed with a variable amount of higher metal content particles derived from the resuspension in the HTZ. In addition, in the HTZ, which acts as a degradation reactor for particulate organic matter, particulate mercury concentrations increase with increasing C:N ratios and amorphous oxyhydroxides particles. Mercury reaches the estuarine HTZ mainly associated with the riverine and marine particles, including organic matter and oxyhydroxides, which are temporarily trapped in the HTZ and mixed with autochthonous HTZ particles. The largest particles periodically settle and undergo diagenetic reactions and resuspensions, which lead to their mercury enrichment. Depending upon hydrodynamic conditions, mercury escapes seaward as fine particulate within the plume, partially associated with the oxyhydroxides. A surface complexation model reproduces most of the partitioning observed. In the dissolved phase the model simulation suggests that a very strong ligand must be present to explain the field observations.

The concentration and distribution of different mercury species in the water columns of BaiHua reservoir

Three study sites were selected at the upper, middle and down reach of the Baihua Reservoir and the water samples from different depth were collected in June 8 to 9, 2002. Dissolved gaseous mercury (DGM), reactive and total mercury concentrations in water profiles were measured by trap pre-concentration and CVAFS detection method. The results indicated, as a whole, the concentrations of all mercury species at the three sites gradually decreased along the water flow direction, and the highest concentration site presented in the upper stream (HuaQiao) of the reservoir. In water column (except bottom water), the highest average total and reactive mercury concentrations are 35.9 ng/L and 5.7 ng/L, respectively. Total mercury concentrations in bottom water reach 807-1963 ng/L. Sediments are potential mercury source to water column of the reservoir. A preliminary study indicted that Baihua Reservoir is seriously contaminated in terms of mercury due to mercury discharge from Guizhou Organic Chemical Plant (GOCP). It is essential to carry out further study on mercury cycling in Baihua Reservoir to evaluate ecological effects from mercury contamination.

Mercury Speciation in Sediments of a Tropical Coastal Environment

The speciation of mercury in tropical coastal areas, although scarcely studied, has presented an odd behaviour when compared with the results obtained in temperate environments. In this work, we measured the concentrations of mercury species (mercuric mercury, methyl-mercury and dimethyl-mercury) in the sediments of Sepetiba Bay (Brazil) and compared these with geochemical parameters. Twenty-eight sediment samples were extracted in an open microwave system and mercury speciation was carried out by ethylation, cryogenic focusing, gas chromatography and quartz furnace atomic absorption spectrometry. Fraction < 63 µm, organic carbon and total sulphur contents and redox potential were measured in order to outline the geochemical characteristics of the sediments. While mercuric mercury presented concentrations ranging between 22.65 and 134.61 ng g−1, methyl-mercury concentrations ranged between < 2.0 and 4.4 ng g−1. Only a few dimethyl-mercury concentrations were relatively high (up to 14.6 ng g−1). The results of mercuric mercury presented an unexpected positive correlation with sulphur contents showing that mercury is not forming stable sulphide complexes, even under very reducing conditions. This would render mercury available for the formation of methyl- or dimethyl-mercury that would be both fixed in the sediments and volatilised.

Inorganic mercury and methylmercury in surface sediments and mussel tissues from a microtidal lagoon (Bizerte, Tunisia)

The aim of this study was to investigate the distribu- tion of mercury compounds in marine sediments and mussel tissues collected in the lagoon of Bizerte, Tunisia, during two seasons (summer and winter). Inorganic mercury (Hg2+) con- centrations in sediments were found to be highly variable, ranging from 0.04 nmol.g -1 to 3.22 nmol.g -1 (dry weight) with a mean value of 0.52 nmol.g -1 . Anthropogenic sources of Hg2+, most probably metallurgy or tire production indus- tries, have been evidenced. The mean concentration of monomethylmercury (MeHg + ) in the surface sediments is 2.32 pmol g -1 ranging from below the detection limit (0.45 pmol.g -1 ) to 14.6 pmol.g -1 . No significant variation was ob- served between winter and summer seasons for both mercury species concentration in the sediments. The Hg 2+ concentra- tions in mussel tissues are also variable, ranging from 0.007 to 1.347 nmol.g -1 (dry weight). The mean concentration is 0.70 nmol.g -1 . In these tissues, Hg 2+ is generally the major com- pound, making up ca. 88% of total mercury concentrations. However, methylmercury concentrations are significant and homogeneous, ranging from 62 to 121 pmol.g -1 (mean 96 pmol.g -1 ). The results suggest that a fraction of the inorganic mercury load in the sediments of the lagoon undergoes meth- ylation pathways. MeHg+ produced is assimilated in the mus- sels more readily than Hg 2+ .

Modelling atmospheric mercury transport and deposition across Europe and the UK

There are inadequate measurements of surface ambient concentrations of mercury species and their deposition rates for the UK deposition budget to be characterized. In order to estimate the overall mercury flux budget for the UK, a simple long-term 1D Lagrangian trajectory model was constructed that treats emissions (1998), atmospheric transformation and deposition across Europe. The model was used to simulate surface concentrations of mercury and deposition across Europe at a resolution of 50 km×50 km and across the UK at 20 km×20 km. The model appeared to perform adequately when compared with the few available measurements, reproducing mean concentrations of elemental gaseous mercury at particular locations and the magnitude of regional gradients. The model showed that 68% of the UK's mercury emissions are exported and 32% deposited within the UK. Of deposition to the UK, 25% originates from the Northern Hemisphere/global background, 41% from UK sources and 33% from other European countries. The total mercury deposition to the UK is in good agreement with other modelling, 9.9 tonne yr −1 cf. 9.0 tonne yr −1, for 1998. However, the attribution differs greatly from the results of other coarser-scale modelling, which allocates 55% of the deposition to the UK from UK sources, 4% from other European countries and 60% from the global background atmosphere. The model was found to be sensitive to the speciation of emissions and the dry deposition velocity of elemental gaseous mercury. The uncertainties and deficiencies are discussed in terms of model parameterization and input data, and measurement data with which models can be validated. There is an urgent requirement for measurements of removal terms, concentrations, and deposition with which models can be parameterized and validated.

A comprehensive Eulerian modelling framework for airborne mercury species: model development and applications in Europe

A comprehensive mercury model system using the Eulerian reference frame of the Acid Deposition and Oxidant Model (ADOM) has been developed under the Canada–Germany Science & Technology Co-operation Agreement and applied within the European Union MArine Science and Technology–BAltic Sea SYstem Study (MAST-III-BASYS) and the Environment & Climate project Mercury Species over Europe (MOE), to study the regional transport and deposition fluxes of atmospheric mercury species. The model is able to simulate long-range transport of mercury over the entire depth of the troposphere with a basic time step of 1 h and incorporates current knowledge of physico-chemical forms and transformation reactions of atmospheric mercury species. Model predicted concentration and deposition pattern of mercury species over Europe are presented and concentrations of total gaseous mercury in ambient air and total mercury in precipitation calculated by the model are compared with observed values from a BASYS monitoring network study in February/March 1998. Concentrations in air agree within a factor of about 2 with observed values, thus indicating that the model is capable of reproducing observations satisfactorily even on an hourly basis. Observed monthly average concentrations in precipitation at four monitoring stations at the Baltic Sea coast are reproduced by the model within a factor of 1.3 suggesting that the chemical scheme in the model is based on an adequate parameterisation of aqueous phase chemistry.

Mercury mine drainage and processes that control its environmental impact

Mine drainage from mercury mines in the California Coast Range mercury mineral belt is an environmental concern because of its acidity and high sulfate, mercury, and methylmercury concentrations. Two types of mercury deposits are present in the mineral belt, silica-carbonate and hot-spring type. Mine drainage is associated with both deposit types but more commonly with the silica-carbonate type because of the extensive underground workings present at these mines. Mercury ores consisting primarily of cinnabar were processed in rotary furnaces and retorts and elemental mercury recovered from condensing systems. During the roasting process mercury phases more soluble than cinnabar are formed and concentrated in the mine tailings, commonly termed calcines. Differences in mineralogy and trace metal geochemistry between the two deposit types are reflected in mine drainage composition. Silica-carbonate type deposits have higher iron sulfide content than hot-spring type deposits and mine drainage from these deposits may have extreme acidity and very high concentrations of iron and sulfate. Mercury and methylmercury concentrations in mine drainage are relatively low at the point of discharge from mine workings. The concentration of both mercury species increases significantly in mine drainage that flows through and reacts with calcines. The soluble mercury phases in the calcines are dissolved and sulfate is added such that methylation of mercury by sulfate reducing bacteria is enhanced in calcines that are saturated with mine drainage. Where mercury mine drainage enters and first mixes with stream water, the addition of high concentrations of mercury and sulfate generates a favorable environment for methylation of mercury. Mixing of oxygenated stream water with mine drainage causes oxidation of dissolved iron(II) and precipitation of iron oxyhydroxide that accumulates in the streambed. Both mercury and methylmercury are strongly adsorbed onto iron oxyhydroxide over the pH range of 3.2–7.1 in streams impacted by mine drainage. The dissolved fraction of both mercury species is depleted and concentrated in iron oxyhydroxide such that the amount of iron oxyhydroxide in the water column reflects the concentration of mercury species. In streams impacted by mine drainage, mercury and methylmercury are transported and adsorbed onto particulate phases. During periods of low stream flow, fine-grained iron hydroxide sediment accumulates in the bed load of the stream and adsorbs mercury and methylmercury such that both forms of mercury become highly enriched in the iron oxyhydroxide sediment. During high-flow events, mercury- and methylmercury-enriched iron hydroxide sediment is transported into larger aquatic systems producing a high flux of bioavailable mercury.

A methodological study of mercury speciation using dogfish liver CRM (DOLT-2).

The purpose of the study was to optimise analytical methods for determination of the chemical speciation of mercury in studies of protective mechanisms of selenium. Optimisation of the methods was performed using CRM DOLT-2 (Dogfish liver), both in its original form and after separation of various fractions. The sample was homogenised with 10 mM Tris-HCl buffer (pH 7.6) and ultracentrifuged. The soluble phase obtained was applied to a size exclusion chromatography column (Sephadex G-75 column) for separation of various protein fractions. Total mercury (total Hg), monomethyl mercury (MeHg) and selenium (Se) were determined in whole dogfish liver tissue and its soluble and insoluble phases (pellet). Different approaches for determination of total Hg and MeHg were compared. Simultaneous determination of MeHg and inorganic mercury (Hg2+) was based on alkaline dissolution and/or acid leaching, followed by ethylation, room temperature precollection, isothermal gas chromatography (GC), pyrolysis and detection with cold vapour atomic fluorescence spectrometry (CVAFS). The sum of MeHg and Hg2+ was compared to total Hg results obtained by acid digestion and CVAAS detection. The accuracy of MeHg determination was checked by its determination using acid leaching at room temperature, solvent extraction, back extraction into Milli-Q water, ethylation, GC and CVAFS detection. For the insoluble phase it is recommended to use solvent extraction for MeHg and acid digestion CVAAS for total Hg. For determination of MeHg and Hg2+ in the lyophilised sample and water soluble fractions containing low concentrations of mercury species, the simultaneous measurement of MeHg and Hg2+ after alkaline dissolution is the most appropriate method.

Flow injection-liquid chromatography-cold vapour atomic absorption spectrometry for rapid determination of methyl and inorganic mercury

A previously described system for determining low concentrations of mercury species in environmental samples using flow injection high-performance liquid chromatography cold vapour atomic absorption spectrometry (FI-HPLC-CVAAS) has been further developed with respect to time of analysis, long term signal stability, memory effects, detection limits, and environmental friendliness. Methyl and inorganic mercury were determined without pre-treatment in brackish water and in digested biological certified reference materials, DOLT-2 and TORT-2. Results were compared with those obtained by gas chromatography microwave-induced plasma atomic emission spectroscopy (GC-MIP-AES) using either butylation with a Grignard reagent or ethylation with sodium tetraethylborate. With the FI-HPLC-CVAAS system, absolute detection limits are 1.7 pg and 3.4 pg for methyl and inorganic mercury, respectively. Mercury species in a sample can be determined at the 0.4 ng l−1 level within 5 min. For lower concentrations the time for analysis has to be increased.

Biosorption of inorganic mercury and alkylmercury species on to Phanerochaete chrysosporium mycelium

The biosorption of inorganic mercury (HgCl 2), methyl mercury (CH 3HgCl) and ethyl mercury (C 2H 5HgCl) onto the dry biomass of Phanerochaete chryosponum was studied from aqueous media which concentrations in the range of 5–500 mg l −1. The surface charge density varied with pH, and the concentration of mercury species adsorbed significantly increased from pH 3.0 to maximum levels at pH 8.0. The biosorption of mercury ions by Phanerochaete chrysosporium increased as the initial concentration of Hg(II) ion increased in the adsorption medium. A biosorption equilibrium were established after about 6 h, the adsorbed Hg(II) ion did not significantly change further with time. The dissociation constant ( k d) values were 72, 63, and 61 mg l −1 for CH 3HgCl, C 2H 5HgCl and for Hg(II), respectively. The maximum biosorption capacity ( q m) at pH 7.0 was 79 mg for CH 3HgCI, 67 mg for C 2H 5HgCl and 61 mg for Hg(II) per g of dried fungal biomass. The affinity order of mercury species was CH 3HgCl>C 2H 5HgCl>and Hg(II).

Mercury in remote Rocky Mountain lakes of Glacier National Park, Montana, in comparison with other temperate North American regions

We determined concentrations of mercury (Hg) and methylmercury (MeHg) in 12 pristine lakes of Glacier National Park (GNP) and compared our observations with data from published studies of remote lakes in north-central Wisconsin and the Adirondack region of New York. Despite marked differences in water chemistry, biology, and hydrogeology, concentrations of Hg and MeHg in all regions were strongly correlated with dissolved organic carbon (DOC). Variables related to the acid–base status of lake waters had secondary effects on the concentration of waterborne mercury species. Although Hg and MeHg were strongly correlated with DOC in all three regions, MeHg concentrations were lower and increased less per unit organic carbon in GNP lakes than in either Wisconsin or New York. In GNP lakes, MeHg averaged only 4 ± 2% (mean ± SD) of the Hg, while in Wisconsin and New York lakes MeHg averaged 10–14% of the Hg. Based on simple regression modelling, we estimate that the maximum MeHg fraction (MeHg/Hg) in dystrophic GNP lakes would be three- to six-fold lower than in Wisconsin or New York waters of similarly high DOC. Our results suggest that this regional difference involves factors regulating the net production of MeHg in lakes or watersheds.

Concentration of mercury species in relationship to other site‐specific factors in the surface waters of northern Wisconsin lakes

To investigate relationships between mercury speciation and site‐specific factors in temperate freshwaters, we measured the concentration of seven Hg species along with 18 environmental variables in the surface waters of 23 northern Wisconsin lakes during spring and fall. The lakes spanned relatively wide gradients in Hg (0.15–4.8 ng liter −1) and methylmercury (MeHg: 0.04–2.2 ng liter− 1). Over the range of measured variables, Hg and McHg were most strongly correlated with each other (r2 = 0.83–0.88) and with dissolved organic C (DOC) (r2 = 0.64–0.92). Multiple regression models containing DOC and a (DOC × pH) interaction term accounted for 85–90% of the variability in Hg and MeHg between lakes.Observed differences between lakes reflected internal cycling processes and external transport pathways. Internally, high DOC and low pH favored Hg methylation and retention over Hg evasion across the air‐water interface. Externally, watershed mapping suggested that the cotransport of DOC, Hg, and MeHg from riparian wetland was also a potentially important process. Observed seasonal differences indicated a 30% increase in MeHg across lakes during summer due to internal or external processes.The effects of DOC on bioaccumulation may be twofold and antagonistic. Although waterborne Hg and MeHg increased with DOC, seston‐water partition coefficients tended to decrease, indicating disproportionately more Hg in the dissolved phase. These observations are consistent with previous data on bioaccumulation factors for zooplankton and fish.

Specific interactions of mercury chloride with membranes and other ligands as revealed by mercury-NMR

High resolution mercury nuclear magnetic resonance ( 199Hg-NMR) experiments have been performed in order to monitor mercury chemical speciation when HgCl 2 is added to water solutions and follow mercury binding properties towards biomembranes or other ligands. Variations of 199Hg chemical shifts by several hundred ppm depending upon pH and/or pCl changes or upon ligand or membrane addition afforded to determine the thermodynamic parameters which describe the equilibria between the various species in solution. By comparison to an external reference, the decrease in concentration of mercury species in solution allowed to estimate the amount as well as the thermodynamic paramaters of unlabile mercury-ligand or mercury-membrane complexes. Hence, some buffer molecules can be classified in a scale of increasing complexing power towards Hg(II): EGTA > Tris > HEPES. In contrast, MOPS, Borax, phosphates and acetates show little complexation properties for mercury, in our experimental conditions. Evidence for complexation with phosphatidylethanolamine (PE), phosphatidylserine (PS) and human erythrocyte membranes has been found. Hg(II) does not form complexes with egg phosphatidylcholine membranes. Interaction with PE and PS model membranes can be described by the presence of two mercury sites, one labile, the other unlabile, in the NMR time scale. In the labile site Hg(PE) and Hg(PS) 2 would be formed whereas in the unlabile site Hg(II) would establish bridges between three PE or PS molecules. Calculated thermodynamic data clearly indicate that PE is a better complexing agent than PS. Evidence is also found that complexation with lipids uses at first the HgCl 2 species. Interestingly, mercury complexation with ligands or membranes can be completely reversed by addition of decimolar NaCl solutions. Minute mechanisms for mercury complexation with the primary amine of PE or PS membrane head groups are discussed.

Proportion of methylmercury to the total amount of mercury in river waters in Canada and Japan

The proportions of methylmercury to the total amount of mercury in water were determined for three rivers and were found to be similar (around 30%). The proportion in sewage effluent water showed a similar value. A pretreatment procedure which can analyze a low concentration of mercury and various species of mercury compounds in natural water is described. The mercury concentration in once mercury-polluted rivers was reduced considerably to near background levels (Ottawa River: 6.6 ng l −1; Suimon River: 26.2 ng l −1).