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  • 1.
    Adediran, Gbotemi A.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Liem-Nguyen, Van
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Song, Yu
    Schaefer, Jeffra K.
    Slcyllberg, Ulf
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Microbial Biosynthesis of Thiol Compounds: Implications for Speciation, Cellular Uptake, and Methylation of Hg(II)2019In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 53, no 14, p. 8187-8196Article in journal (Refereed)
    Abstract [en]

    Cellular uptake of inorganic divalent mercury (Hg(II)) is a key step in microbial formation of neurotoxic methylmercury (MeHg), but the mechanisms remain largely unidentified. We show that the iron reducing bacterium Geobacter sulfurreducens produces and exports appreciable amounts of low molecular mass thiol (LMM-RSH) compounds reaching concentrations of about 100 nM in the assay medium. These compounds largely control the chemical speciation and bioavailability of Hg(II) by the formation of Hg(LMM-RS)<INF><INF><INF>2</INF></INF> </INF>complexes (primarily with cysteine) in assays without added thiols. By characterizing these effects, we show that the thermodynamic stability of Hg(II)-complexes is a principal controlling factor for Hg(II) methylation by this bacterium such that less stable complexes with mixed ligation involving LMM-RSH, OH-, and Cl- are methylated at higher rates than the more stable Hg(LMM-RS)<INF>2</INF> complexes. The Hg(II) methylation rate across different Hg(LMM-RS)<INF>2</INF> compounds is also influenced by the chemical structure of the complexes. In contrast to the current perception of microbial uptake of Hg, our results adhere to generalized theories for metal biouptake based on metal complexation with cell surface ligands and refine the mechanistic understanding of Hg(II) availability for microbial methylation.

  • 2.
    Björn, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Baxter, Douglas C
    Frech, Wolfgang
    Umeå University, Faculty of Science and Technology, Chemistry.
    Calibration errors due to variations in peak characteristics in the measurement of transient signals by inductively coupled plasma-scanning mass spectrometry2002In: Journal of Analytical Atomic Spectrometry, Vol. 17, p. 1582-8Article in journal (Refereed)
    Abstract [en]

    The impact of variations in peak characteristics on the fidelity of transient signal measurement by inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS) was investigated. Specifically, the question as to whether the multi-element capabilities or the accuracy in determined analyte amounts were deteriorated compared to what has been reported previously when not considering peak variations was addressed. The peak characteristics considered were the time of the signal maximum (tpeak), the standard deviation of the assumed Gaussian input function generated by the sample introduction system (G), and the time constant for signal decay (). Investigations of simulated exponentially-modified Gaussian peaks revealed that, for variations of peak characteristics within reasonable ranges, measurement noise and variations in tpeak, G and all contributed to calibration uncertainty. Electrothermal vaporisation (ETV) and flow injection (FI) systems were used to experimentally generate transient signals of varying peak characteristics. Removing data points from the raw signals simulated the monitoring of up to 100 mass-to-charge ratios, allowing calibration data and analyte amounts to be determined from the processed signals. To obtain calibration graph slopes with relative standard deviations below 1% for the ETV-ICP-QMS system, it was found necessary to acquire 7–24 data points per peak for 50–5 ms dwell times. On this basis, the maximum number of mass-to-charge ratios that could be monitored in a typical ETV-ICP-QMS analysis was 4–10 using dwell times of 50–5 ms. With the FI-ICP-QMS system, variations in the peak characteristics between calibration standards and samples meant that, to obtain less than 3% error in determined analyte amounts, at least 7 or 10 points per peak were required for external and internal standardisation, respectively. It was found that variations in peak characteristics contributed more than measurement noise to the error in determined analyte amounts. In recent studies it has been reported that 3–4 data points per peak are sufficient to accurately monitor a transient if peak variations are not considered, which, for typical ETV signals, would allow the monitoring of 20 mass-to-charge ratios during a single measurement cycle. Thus the results obtained here show that the multi-element capability of ICP-QMS when monitoring transient signals can be severely compromised by such variations.

  • 3.
    Björn, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Frech, Wolfgang
    Umeå University, Faculty of Science and Technology, Chemistry.
    Introduction of high carbon content solvents into inductively coupled plasma mass spectrometry by a direct injection high efficiency nebuliser2003In: Analytical and Bioanalytical Chemistry, Vol. 376, no 2, p. 274-8Article in journal (Refereed)
    Abstract [en]

    A preliminary investigation on the introduction of high carbon content solvents into inductively coupled plasma mass spectrometry (ICP-MS) by a direct injection high efficiency nebuliser (DIHEN) is presented. Ethanol, hexane, toluene and a natural gas condensate were introduced using a flow injection system. The performance for determinations of total concentrations of mercury present in organic solvents as different species was evaluated. The most critical operating parameters were the nebuliser gas flow rate and amount of oxygen added to the plasma. For the DIHEN a nebuliser gas flow rate of 0.3 L minm1 and 50 mL minm1 of oxygen added to the plasma auxiliary gas flow gave stable conditions and high analyte sensitivity. Species recoveries for HgCl2, CH3HgCl, (CH3)2Hg and Hg0 in hexane were 99-4, 101-4, 95-4 and 104-7%, respectively. Detection limit for mercury in hexane was 85 pg mLm1 based on 3† of a 201Hg-spiked blank. A gradual deposition was observed at the nebuliser tip, partly blocking the gas annulus. The rate of deposition seemed to be related to the amount of carbon introduced through the nebuliser. With the optimised conditions used in this work, the nebuliser could be used for approximately 50 hexane samples before cleaning was necessary.

  • 4.
    Björn, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Frech, Wolfgang
    Umeå University, Faculty of Science and Technology, Chemistry.
    Non-spectral interference effects in inductively coupled plasma mass spectrometry using direct injection high efficiency and microconcentric nebulisation2001In: JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol. 16, p. 4-11Article in journal (Refereed)
    Abstract [en]

    Non-spectral interference effects in inductively coupled plasma mass spectrometry (ICP-MS) were investigated for the direct injection high efficiency nebuliser (DIHEN) the large bore DIHEN (LB-DIHEN) and a microconcentric nebuliser (MCN) with a cyclone spray chamber. Interference effects from nitric and sulfuric acid, methanol and sodium nitrate solutions were studied. Eight elements with different ionisation potentials (IP) and atomic masses were monitored at various nebuliser gas flow rates. The processes giving rise to interference effects observed with the DIHEN were investigated by monitoring relative analyte sensitivities at different radial plasma positions. It was found that the average magnitude of interference effects decreased in the order MCN approximate to DIHEN > LB-DIHEN, showing that analytical performance is improved by removing the spray chamber. It is suggested that remaining interference effects observed for the DIHEN are caused by a matrix induced spatial redistribution of the aerosol in the plasma due to differences in droplet. size distribution and density between water and the matrix solutions. In addition, the high plasma solvent load with the DIHEN results in a pronounced negative correlation between relative analyte signal magnitude and IP. For the LB-DIHEN, these effects were smaller, and other element specific interference effects dominated. For the eight elements monitored, element specific interference effects increased in the order MCN < DIHEN < LB-DIHEN. Transient acid effects were also investigated and found to be virtually eliminated by the use of a DIHEN instead of the MCN system. For the latter, stabilisation times of 3-10 mill were necessary when changing the nitric acid concentration between 0.22 and 2.2 mol 1(-1).

  • 5.
    Björn, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Larsson, Tom
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lambertsson, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    Skyllberg, Ulf
    Frech, Wolfgang
    Umeå University, Faculty of Science and Technology, Chemistry.
    Recent Advances in Mercury Speciation Analysis with Focus on Spectrometric Methods and Enriched Stable Isotope Applications2007In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 36, no 6, p. 443–51-Article in journal (Refereed)
    Abstract [en]

    This paper discusses some recent advances in spectrometric methods and approaches for mercury speciation analysis of environmental samples with focus on isotope dilution techniques for determination of mercury species' concentrations in gaseous samples and reaction rates in soils and sediments. Such analytical data is important inter alia in fundamental research on mercury biogeochemistry and for risk assessments of mercury-contaminated soils and sediments and for designing effective remedial actions. The paper describes how the use of enriched stable isotope tracers in mercury speciation analysis can improve the traceability and accuracy of results, facilitate rational method developments, and be useful for studying biogeochemical processes, i.e. rate of reactions and fluxes, of mercury species. In particular the possibilities to study and correct for unwanted species transformation reactions during sample treatment and to study “natural” transformations of species in environmental samples, or micro- and mesocosm ecosystems, during incubations are highlighted. Important considerations to generate relevant data in isotope tracer experiments as well as reliability and quality assurance of mercury speciation analysis in general are also discussed.

  • 6.
    Björn, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nygren, Yvonne
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nhu Nguyen, Tam Trinh Thi
    Umeå University, Faculty of Science and Technology, Chemistry.
    Ericson, Christer
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nöjd, Mikael
    Kirurgi.
    Naredi, Peter
    Kirurgi.
    Determination of platinum in human subcellular microsamples by inductively coupled plasma mass spectrometry2007In: Analytical Biochemistry, Vol. 363, p. 135-42Article in journal (Refereed)
    Abstract [en]

    A fast and robust method for the determination of platinum in human subcellular microsamples by inductively coupled plasma mass spectrometry was developed, characterized, and validated. Samples of isolated DNA and exosome fractions from human ovarian (2008) and melanoma (T289) cancer cell lines were used. To keep the sample consumption to approximately 10 μl and obtain a high robustness of the system, a flow injection sample introduction system with a 4.6-μl sample loop was used in combination with a conventional pneumatic nebulizer and a spray chamber. The system was optimized with respect to signal/noise ratio using a multivariate experimental design. The system proved to be well suited for routine analysis of large sample series, and several hundreds of samples could be analyzed without maintenance or downtime. The detection limit of the method was 0.12 pg (26 pg/g) platinum. To avoid systematic errors from nonspectral interferences, it was necessary to use reagent matched calibration standards or isotope dilution analysis. An uncertainty budget was constructed to estimate the total expanded uncertainty of the method, giving a quantification limit of 2.3 pg (0.5 ng/g) platinum in DNA samples. The uncertainty was sufficiently low to study quantitative differences in the formation of Pt–DNA adducts after treatment with cisplatin using different exposure times and concentrations.

  • 7.
    Bouchet, Sylvain
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Analytical developments for the determination of monomethylmercury complexes with low molecular mass thiols by reverse phase liquid chromatography hyphenated to inductively coupled plasma mass spectrometry2014In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1339, p. 50-58Article in journal (Refereed)
    Abstract [en]

    The behavior of monomethylmercury (MMHg) is markedly influenced by its distribution among complexes with low molecular mass (LMM) thiols but analytical methodologies dedicated to measure such complexes are very scarce up to date. In this work, we selected 15 LMM thiols often encountered in living organisms and/or in the environment and evaluated the separation of the 15 corresponding MMHg-thiol complexes by various high performance liquid chromatography (HPLC) columns. Two C18 (Phenomenex Synergi Hydro-RP and LunaC18(2)), two phenyl (Inertsil Ph 3 and 5 mu m) and one mixed-mode (Restek Ultra IBD) stationary phases were tested for their retention and resolution capacities of the various complexes. The objective was to find simple separation conditions with low organic contents in the mobile phase to provide optimal conditions for detection by inductively coupled plasma mass spectrometry (ICPMS). The 15 complexes were synthesized in solution and characterized by electrospray ionization-mass spectrometry (ESI-MS). The C18 columns tested were either not resolutive enough or too retentive. The 3 pm phenyl stationary phase was able to resolve 10 out of the 15 complexes in less than 25 min, under isocratic conditions. The mixed-mode column was especially effective at separating the most hydrophilic complexes (6 complexes out of the 15), corresponding to the main LMM thiols found in living organisms. The detection limits (DLs) for these two columns were in the low nanomolar range and overall slightly better for the phenyl column. The possibilities offered by such methodology were exemplified by monitoring the time-course concentrations of four MMHg-thiol complexes within a phytoplankton incubation containing MMHg in the presence of an excess of four added thiols. 

  • 8. Bravo, Andrea G.
    et al.
    Bouchet, Sylvain
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tolu, Julie
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mateos-Rivera, Alejandro
    Bertilsson, Stefan
    Molecular composition of organic matter controls methylmercury formation in boreal lakes2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 14255Article in journal (Refereed)
    Abstract [en]

    A detailed understanding of the formation of the potent neurotoxic methylmercury is neededto explain the large observed variability in methylmercury levels in aquatic systems. While it is known that organic matter interacts strongly with mercury, the role of organic matter composition in the formation of methylmercury in aquatic systems remains poorly understood. Here we show that phytoplankton-derived organic compounds enhance mercurymethylation rates in boreal lake sediments through an overall increase of bacterial activity. Accordingly, in situ mercury methylation defines methylmercury levels in lake sediments strongly influenced by planktonic blooms. In contrast, sediments dominated by terrigenous organic matter inputs have far lower methylation rates but higher concentrations of methylmercury, suggesting that methylmercury was formed in the catchment and imported into lakes. Our findings demonstrate that the origin and molecular composition of organic matter are critical parameters to understand and predict methylmercury formation and accumulation in boreal lake sediments.

  • 9. Bravo, Andrea G.
    et al.
    Loizeau, Jean-Luc
    Dranguet, Perrine
    Makri, Stamatina
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ungureanu, Viorel Gh.
    Slaveykova, Vera I.
    Cosio, Claudia
    Persistent Hg contamination and occurrence of Hg-methylating transcript (hgcA) downstream of a chlor-alkali plant in the Olt River (Romania)2016In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 23, no 11, p. 10529-10541Article in journal (Refereed)
    Abstract [en]

    Chlor-alkali plants using mercury (Hg) cell technology are acute point sources of Hg pollution in the aquatic environment. While there have been recent efforts to reduce the use of Hg cells, some of the emitted Hg can be transformed to neurotoxic methylmercury (MeHg). Here, we aimed (i) to study the dispersion of Hg in four reservoirs located downstream of a chlor-alkali plant along the Olt River (Romania) and (ii) to track the activity of bacterial functional genes involved in Hg methylation. Total Hg (THg) concentrations in water and sediments decreased successively from the initial reservoir to downstream reservoirs. Suspended fine size particles and seston appeared to be responsible for the transport of THg into downstream reservoirs, while macrophytes reflected the local bioavailability of Hg. The concentration and proportion of MeHg were correlated with THg, but were not correlated with bacterial activity in sediments, while the abundance of hgcA transcript correlated with organic matter and Cl- concentration, indicating the importance of Hg bioavailability in sediments for Hg methylation. Our data clearly highlights the importance of considering Hg contamination as a legacy pollutant since there is a high risk of continued Hg accumulation in food webs long after Hg-cell phase out.

  • 10. Bravo, Andrea G.
    et al.
    Peura, Sari
    Buck, Moritz
    Ahmed, Omneya
    Mateos-Rivera, Alejandro
    Ortega, Sonia Herrero
    Schaefer, Jeffra K.
    Bouchet, Sylvain
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tolu, Julie
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bertilsson, Stefan
    Methanogens and iron-reducing bacteria: the overlooked members of mercury-methylating microbial communities in boreal lakes2018In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 84, no 23, article id e01774-18Article in journal (Refereed)
    Abstract [en]

    ABSTRACT: Methylmercury is a potent human neurotoxin which biomagnifies in aquatic food webs. Although anaerobic microorganisms containing the hgcA gene potentially mediate the formation of methylmercury in natural environments, the diversity of these mercury-methylating microbial communities remains largely unexplored. Previous studies have implicated sulfate-reducing bacteria as the main mercury methylators in aquatic ecosystems. In the present study, we characterized the diversity of mercury-methylating microbial communities of boreal lake sediments using high-throughput sequencing of 16S rRNA and hgcA genes. Our results show that in the lake sediments, Methanomicrobiales and Geobacteraceae also represent abundant members of the mercury-methylating communities. In fact, incubation experiments with a mercury isotopic tracer and molybdate revealed that only between 38% and 45% of mercury methylation was attributed to sulfate reduction. These results suggest that methanogens and iron-reducing bacteria may contribute to more than half of the mercury methylation in boreal lakes.

    IMPORTANCE: Despite the global awareness that mercury, and methylmercury in particular, is a neurotoxin to which millions of people continue to be exposed, there are sizable gaps in the understanding of the processes and organisms involved in methylmercury formation in aquatic ecosystems. In the present study, we shed light on the diversity of the microorganisms responsible for methylmercury formation in boreal lake sediments. All the microorganisms identified are associated with the processing of organic matter in aquatic systems. Moreover, our results show that the well-known mercury-methylating sulfate-reducing bacteria constituted only a minor portion of the potential mercury methylators. In contrast, methanogens and iron-reducing bacteria were important contributors to methylmercury formation, highlighting their role in mercury cycling in the environment.

  • 11.
    Drott, Andreas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bouchet, Sylvain
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    SLU.
    Refining Thermodynamic Constants for Mercury(II)-Sulfides in Equilibrium with Metacinnabar at Sub-Micromolar Aqueous Sulfide Concentrations2013In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 47, no 9, p. 4197-4203Article in journal (Refereed)
    Abstract [en]

    An important issue in mercury (Hg) biogeochemistry is to explore the influence of aqueous Hg(II) forms on bacterial uptake, and subsequent methyl mercury formation, under iron(III) and sulfate reducing conditions. The success of this is dependent on relevant information on the thermodynamic stability of Hg-sulfides. In the present study, we determined the solubility of a commercially available HgS(s) phase, which was shown by X-ray diffraction to be a mixture of 83% metacinnabar and 17% cinnabar. At aqueous sulfide concentrations between 0.060 and 84 µM, well below levels in previous studies, we report a solubility product (log Ksp±SE) of -36.8±0.3 (HgS(s) + H+ = Hg2+ + HS-, I=0, T=25°C, pH 6-10, n=20) for metacinnabar. This value is 0.7 log units higher than previous estimates. Complementing our data with data from Paquette and Helz (1997), we took advantage of a large data set (n=65) covering a wide range of aqueous sulfide (0.06 µM-140 mM), and pH (1-11). Based on this we report refined formation constants (±SE) for the three aqueous Hg(II)-sulfide species proposed by Schwarzenbach and Widmer (1963): Hg2+ + 2HS- = Hg(SH)20; log K = 39.1±0.1, Hg2+ + 2HS- = HgS2H- + H+; log K = 32.5±0.1, Hg2+ + 2HS- = HgS22- + 2H+; log K = 23.2±0.1. Our refined log K values differ from previous estimates by 0.2-0.6 log units. Furthermore, at the low sulfide concentrations in our study we could rule out the value of -10.0 for the reaction HgS(s) + H2O = HgOHSH(aq), as reported by Dyrssén and Wedborg (1991). By establishing a solubility product for the most environmentally relevant HgS(s) phase, metacinnabar, and extending the range of aqueous sulfide concentrations to sub-µM levels, relevant for soils, sediments and waters, this study decreases the uncertainty in stability constants for Hg-sulfides, thereby improving the basis for understanding the bioavailability and mobility of Hg(II) in the environment.

  • 12. Drott, Andreas
    et al.
    Lambertsson, Lars
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Do Potential Methylation Rates Reflect Accumulated Methyl Mercury in Contaminated Sediments?2008In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 42, no 1, p. 153-158Article in journal (Refereed)
    Abstract [en]

    Relationships between the short-term mono-methyl mercury (MeHg) production, determined as the specific, potential methylation rate constant Km (day−1) after 48 h of incubation with isotope-enriched 201Hg(II) at 23 °C, and the long-term accumulation of ambient MeHg, were investigated in contaminated sediments. The sediments covered a range of environments from small freshwater lakes to large brackish water estuaries and differed with respect to source and concentration of Hg, salinity, primary productivity, quantity and quality of organic matter, and temperature climate. Significant (p < 0.001), positive relationships were observed between Km (day−1) and the concentration of MeHg normalized to total Hg (%MeHg) for surface sediments (0–10, 0–15, and in one case 0–20 cm) across all environments, and across subsets of organic and minerogenic freshwaters. This suggests that the methylation process (MeHg production) overruled demethylation and net transport processes in the surface sediments. The lack of a relationship between Km and %MeHg in two brackish water sediment depth profiles (0–100 cm) indicates that demethylation and the net effect of input−output are relatively more important at greater depths. Differences in the primary production and subsequent availability of easily degradable organic matter (serving as electron donor for methylating bacteria) was indicated to be the most important factor behind observed differences in %MeHg and Km among sites. In contrast, concentrations of sulfate were not correlated to Km, %MeHg, or absolute concentrations of MeHg. We conclude that total concentrations of Hg are of importance for the long-term accumulation of MeHg, and that %MeHg in surface sediments can be used as a proxy for the rate of methylation, across a range of sites from different environments.

  • 13. Drott, Andreas
    et al.
    Lambertsson, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Skyllberg, Ulf
    Effects of oxic and anoxic filtration on determined methyl mercury concentrations in sediment pore waters2007In: Marine Chemistry, Vol. 103, p. 76-83Article in journal (Refereed)
    Abstract [en]

    Accurate determination of methyl mercury (MeHg) concentrations in sediment pore waters is crucial for an improved understanding of mercury (Hg) biogeochemistry, and for improved risk assessment of Hg contaminated sites. In the present study, effects of oxic (air) and anoxic (N2) filtration (after centrifugation) on determined pore water MeHg concentrations were investigated in severely Hg contaminated pulp fibre sediments from two estuaries of the Bothnian Sea, Sweden. MeHg was determined in the filtrate using species-specific isotope dilution gas chromatography inductively coupled plasma mass spectrometry (SSID–GC–ICPMS), after ethylation with sodium tetraethylborate. Determined concentrations of MeHg were greater after anoxic filtration than after oxic filtration for all samples investigated, with MeHg(N2)/MeHg(air) ratios ranging between 3.4 and 343. Adsorption to newly formed Fe(III)/Mn(III/IV)-oxy/hydroxide surfaces is proposed as the main mechanism responsible for MeHg removal during oxic filtration. This is supported by decreases in dissolved Fe and Mn concentrations during oxic filtration, and by decreases in dissolved sulphur concentrations during oxic filtration in the samples with largest effect on MeHg concentrations. The latter is explained by adsorption of SO42− to newly formed Fe(III)/Mn(III/IV)-oxy/hydroxide surfaces. The effect of oxidation during filtration on pore water MeHg concentrations was largest in samples in which FeS(s) was not present, but with calculated pe-values below − 3. Thus, our results indicate that the largest errors with respect to pore water MeHg concentrations when filtering in air can be expected in samples with an intermediate redox potential, possibly buffered by a mixture of oxidation sensitive Fe(II/III) minerals.

  • 14. Drott, Andreas
    et al.
    Lambertsson, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Skyllberg, Ulf
    Importance of Dissolved Neutral Mercury Sulfides for Methyl Mercury Production in Contaminated Sediments2007In: Environmental Science and Technology, Vol. 41, no 7, p. 2270-6Article in journal (Refereed)
    Abstract [en]

    Biotic transformation of inorganic mercury, Hg(II), to mono methyl mercury (MeHg) is proposed to be largely controlled by passive uptake of neutral Hg complexes by sulfate reducing bacteria (SRB). In this study, the chemical speciation of Hg(II) in seven locally contaminated sediments covering environments such as (i) brackish water, (ii) low-productivity freshwater, and, (iii) high-productivity freshwater was related to potential Hg methylation rates, determined by incubation at 23 C for 48 h under N2(g), and to total MeHg concentrations in sediments. Pore water speciation was modeled considering Hg complexes with halides, organic thiols [Hg(SR)2(aq), associated to dissolved organic matter], monosulfides, and bisulfides. The sum of neutral mercury sulfides [Hg(SH)20(aq)] and [HgS0(aq)] was significantly, positively (p < 0.001, n = 20) correlated to the specific methylation rate constant (Km, day-1) at depths of 5-100 cm in two brackish water sediments. Total Hg, total mercury sulfides or Hg(SR)2(aq) in pore water gave no significant relationships with Km. In two sub-sets of freshwater sediments, neutral mercury sulfides were positively correlated to total Hg in pore water, and therefore, total Hg also gave significant relationships with Km. The sum of [Hg(SH)20(aq)] and [HgS0(aq)] was significantly, positively correlated to total sediment MeHg (g kg-1) in brackish waters (p < 0.001, n = 23), in southern, high-productivity freshwaters (p < 0.001, n = 20), as well as in northern, low-productivity freshwater (p = 0.048, n = 6). The slopes (b, b') of the relationships Km (day-1) = a + b([Hg(SH)20(aq)] + [HgS0(aq)]) and MeHg (g kg-1) = a' + b'([Hg(SH)20(aq)] + [HgS0(aq)]) showed an inverse relationship with the C/N ratio, supposedly reflecting differences in primary production and energy-rich organic matter availability among sites. We conclude that concentrations of neutral inorganic mercury sulfide species, together with the availability of energy-rich organic matter, largely control Hg methylation rates in contaminated sediments. Furthermore, Hg(SH)20(aq) is suggested to be the dominant species taken up by MeHg producing bacteria in organic-rich sediments without formation of HgS(s).

  • 15. Drott, Andreas
    et al.
    Lambertsson, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Skyllberg, Ulf
    Potential demethylation rate determinations in relation to concentrations of MeHg, Hg and pore water speciation of MeHg in contaminated sediments2008In: Marine Chemistry, Vol. 112, no 1-2, p. 93-101Article in journal (Refereed)
    Abstract [en]

    Specific, potential demethylation rate constants (kd, day− 1) were determined in fresh and brackish water sediments from seven different sites in Sweden originally contaminated with either Hg0(l) or phenyl-Hg. Variations in kd among and within sites were related to ambient concentrations of Hg (1–1143 nmol g− 1) and MeHg (4.4–575pmol g− 1), and to pore water speciation of MeHg. Chemical speciation modeling revealed that MeHgSH(aq), MeHgS−(aq) and MeHg–thiol complexes [MeHgSR(aq)] associated to dissolved organic matter were the dominant MeHg species in the sediment pore water at all sites. Potential rates of MeHg demethylation were determined as the decomposition of isotopically enriched Me204HgCl during 48 h of incubation in darkness under N2(g) at 23 °C. There was a significant (p < 0.001) positive relationship between ambient MeHg concentrations in sediments and kd across all sites, but no significant relationship between ambient Hg and kd. At the three sites with the highest ambient Hg concentrations in sediments (average ± SD, 185 ± 249 nmol g− 1), kd was not significantly correlated with pore water MeHg speciation. At sites with lower concentrations of ambient Hg in sediments (average ± SD, 11 ± 8.4 nmol g− 1), there was a significant (p = 0.02) positive relationship between calculated concentrations of MeHgSH(aq), MeHgS−(aq), or the sum of these two species, and kd. If it is assumed that an oxidative demethylation process dominated at sites with lower concentrations of ambient Hg in sediments, the results suggest that it may be dependent on a passive uptake of inorganic MeHgSH molecules. It was shown that additions of different amounts of MeHg and Hg tracers, in relation to the ambient concentrations of MeHg and Hg, could result in dramatically different kd values within and between sites. At one brackish water site, both absolute demethylation rates and kds were significantly, inversely related to ambient concentrations of MeHg (and Hg). In contrast, at another brackish water site with generally less kds, samples with low ambient MeHg experienced toxic effects and demethylation was not detected. This implies that added (and possibly ambient) MeHg/Hg, depending on the environmental conditions, may have either stimulating or inhibitory effects on demethylation processes.

  • 16.
    Edo, Mar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per-Erik
    Jansson, Stina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Assessment of chemical and material contamination in waste wood fuels: a case study ranging over nine years2016In: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 49, p. 311-319Article in journal (Refereed)
    Abstract [en]

    The increased demand for waste wood (WW) as fuel in Swedish co-combustion facilities during the last years has increased the import of this material. Each country has different laws governing the use of chemicals and therefore the composition of the fuel will likely change when combining WW from different origins. To cope with this, enhanced knowledge is needed on WW composition and the performance of pre-treatment techniques for reduction of its contaminants. In this study, the chemical and physical characteristics of 500 WW samples collected at a co-combustion facility in Sweden between 2004 and 2013 were investigated to determine the variation of contaminant content over time. Multivariate data analysis was used for the interpretation of the data. The concentrations of all the studied contaminants varied widely between sampling occasions, demonstrating the highly variable composition of WW fuels. The efficiency of sieving as a pre-treatment measure to reduce the levels of contaminants was not sufficient, revealing that sieving should be used in combination with other pre-treatment methods. The results from this case study provide knowledge on waste wood composition that may benefit its management. This knowledge can be applied for selection of the most suitable pre-treatments to obtain high quality sustainable WW fuels.

  • 17.
    Edwin, Aaron
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Rompikuntal, Pramod
    Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Stier, Gunter
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wai, Sun Nyunt
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Sauer-Eriksson, Elisabeth A.
    Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Calcium binding by the PKD1 domain regulates interdomain flexibility in Vibrio cholerae metalloprotease PrtV2013In: FEBS Open Bio, E-ISSN 2211-5463, Vol. 3, p. 263-270Article in journal (Refereed)
    Abstract [en]

    Vibrio cholerae, the causative agent of cholera, releases several virulence factors including secreted proteases when it infects its host. These factors attack host cell proteins and break down tissue barriers and cellular matrix components such as collagen, laminin, fibronectin, keratin, elastin, and they induce necrotic tissue damage. The secreted protease PrtV constitutes one virulence factors of V. cholerae. It is a metalloprotease belonging to the M6 peptidase family. The protein is expressed as an inactive, multidomain, 102 kDa pre-pro-protein that undergoes several N- and C-terminal modifications after which it is secreted as an intermediate variant of 81 kDa. After secretion from the bacteria, additional proteolytic steps occur to produce the 55 kDa active M6 metalloprotease. The domain arrangement of PrtV is likely to play an important role in these maturation steps, which are known to be regulated by calcium. However, the molecular mechanism by which calcium controls proteolysis is unknown. In this study, we report the atomic resolution crystal structure of the PKD1 domain from V. cholera PrtV (residues 755–838) determined at 1.1 Å. The structure reveals a previously uncharacterized Ca2+-binding site located near linker regions between domains. Conformational changes in the Ca2+-free and Ca2+-bound forms suggest that Ca2+-binding at the PKD1 domain controls domain linker flexibility, and plays an important structural role, providing stability to the PrtV protein.

  • 18. Eklöf, Karin
    et al.
    Bishop, Kevin
    Bertilsson, Stefan
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Buck, Moritz
    Umeå University, Faculty of Science and Technology, Department of Chemistry. National Bioinformatics Infrastructure Sweden, Uppsala SE-75236, Sweden.
    Skyllberg, Ulf
    Osman, Omneya A.
    Kronberg, Rose-Marie
    Bravo, Andrea G.
    Formation of mercury methylation hotspots as a consequence of forestry operations2018In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 613-614, p. 1069-1078Article in journal (Refereed)
    Abstract [en]

    Earlier studies have shown that boreal forest logging can increase the concentration and export of methylmercury (MeHg) in stream runoff. Here we test whether forestry operations create soil environments of high MeHg net formation associated with distinct microbial communities. Furthermore, we test the hypothesis that Hg methylation hotspots are more prone to form after stump harvest than stem-only harvest, because of more severe soil compaction and soil disturbance. Concentrations of MeHg, percent MeHg of total Hg (THg), and bacterial community composition were determined at 200 soil sampling positions distributed across eight catchments. Each catchment was either stem-only harvested (n = 3), stem-and stump-harvested (n = 2) or left undisturbed (n = 3). In support of our hypothesis, higher MeHg to THg ratios was observed in one of the stump-harvested catchments. While the effects of natural variation could not be ruled out, we noted that most of the highest % MeHg was observed in water-filled cavities created by stump removal or driving damage. This catchment also featured the highest bacterial diversity and highest relative abundance of bacterial families known to include Hg methylators. We propose that water-logged and disturbed soil environments associated with stump harvest can favor methylating microorganisms, which also enhance MeHg formation. 

  • 19.
    Elsayed, Moneim
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Frech, Wolfgang
    Umeå University, Faculty of Science and Technology, Chemistry.
    Optimisation of operating parameters for simultaneous multi-element determination of antimony, arsenic, bismuth and selenium by hydride generation, graphite atomiser sequestration atomic absorption spectrometry2000In: JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol. 15, no 6, p. 697-703Article in journal (Refereed)
    Abstract [en]

    Hydride generation, sequestration in graphite tubes and simultaneous multi-element measurement by atomic absorption spectrometry were used for determination of Sb(V), Bi(III), Se(IV), As(III) and As(V) in Millipore or brackish water by a method based on batchwise addition of the samples to a reaction vessel. As the reducing agent, NaBH4 was added at a controlled flow rate. A statistical programme, Modde 4.0, capable of multivariate optimisation of working parameters for the multi-element determination, was used to optimise the concentrations of HCl, the amount of NaBH4, purge gas flow rates, the graphite atomiser's deposition temperature, as well as the temperature of the reaction vessel.

    In general, the concentrations of HCl and the amount of NaBH4 had the greatest impact on the response and several of the working parameters showed interactions. For highest sensitivity different parameters had to be used for the two matrices. Optimum parameter settings in Millipore and brackish water were: concentration of HCl 2.1 and 2.7 mol l(-1), respectively; 2% NaBH4 addition during 120 s (4 ml) or 84 s (2.8 ml), respectively; Ar purge gas flow rate 150 ml min(-1) in both matrices; reaction vessel temperature 16 and 0 degrees C, respectively; and a deposition temperature of 600 and 150 degrees C, respectively. The detection limits were restricted by variations in the blank absorbance. For 2 ml of sample the detection limits in brackish water were 17, 14, 25 and 140 ng l(-1) for As, Se(IV), Bi and Sb, respectively.

  • 20. Fernández-Gómez, Cristal
    et al.
    Drott, Andreas
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Díez, Sergi
    Bayona, Josep M
    Tesfalidet, Solomon
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindfors, Anders
    Skyllberg, Ulf
    Towards Universal Wavelength-Specific Photodegradation Rate Constants for Methyl Mercury in Humic Waters, Exemplified by a Boreal Lake-Wetland Gradient.2013In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 47, no 12, p. 6279-6287Article in journal (Refereed)
    Abstract [en]

    We report experimentally determined first-order rate constants of MeHg photolysis in three waters along a Boreal lake-wetland gradient covering a range of pH (3.8-6.6), concentrations of total organic carbon (TOC 17.5-81 mg L(-1)), total Fe (0.8-2.1 mg L(-1)), specific UV254 nm absorption (3.3-4.2 L mg(-1) m(-1)) and TOC/TON ratios (24-67 g g(-1)). Rate constants determined as a function of incident sunlight (measured as cumulative photon flux of photosynthetically active radiation, PAR) decreased in the order dystrophic lake > dystrophic lake/wetland > riparian wetland. After correction for light attenuation by dissolved natural organic matter (DOM), wavelength-specific (PAR: 400-700 nm, UVA: 320-400 nm and UVB: 280-320 nm) first-order photodegradation rate constants (kpd) determined at the three sites were indistinguishable, with average values (±SE) of 0.0023 ± 0.0002, 0.10 ± 0.024 and 7.2 ± 1.3 m(2) E(-1) for kpdPAR, kpdUVA, and kpdUVB, respectively. The relative ratio of kpdPAR, kpdUVA, and kpdUVB was 1:43:3100. Experiments conducted at varying MeHg/TOC ratios confirm previous suggestions that complex formation with organic thiol groups enhances the rate of MeHg photodegradation, as compared to when O and N functional groups are involved in the speciation of MeHg. We suggest that if the photon fluxes of PAR, UVA, and UVB radiation are separately determined and the wavelength-specific light attenuation is corrected for, the first-order rate constants kpdPAR, kpdUVA, and kpdUVB will be universal to waters in which DOM (possibly in concert with Fe) controls the formation of ROS, and the chemical speciation of MeHg is controlled by the complexation with DOM associated thiols.

  • 21.
    Goitom, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Comparison of aerosol properties and ICP-MS analytical performance of the Vulkan direct injection nebuliser and the Direct Injection High Efficiency Nebuliser2007In: Journal of Analytical Atomic Spectrometry, Vol. 22, p. 250-7Article in journal (Refereed)
    Abstract [en]

    Monodisperse polymer particles consisting of DVB and styrene-copoly-DVB were successfully synthesized by photoinitiated precipitation polymerization with 2,2'-azobis(2-methylpropionitrile) (AIBN) as initiator. A focused 150 W xenon short arc lamp was used to radiate the sample mixtures. The size of the particles ranged from 1.5 to 4 m and could be varied by changing the monomer concentration between 2 and 10% (v/v) and by means of the time of polymerization. By using photoinitiation instead of thermal initiation, it was possible to avoid coagulum and arrive at spherical particles with an exceptionally high monodispersity for particles of this size range (polydispersity index < 1.02) and with monomer loadings well above 5%.

  • 22.
    Goitom, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Frech, Wolfgang
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    de Loos-Vollebregt, Margaretha T.C.
    Delft University of Technology, Faculty of Applied Sciences, Julianalaan, The Netherlands.
    Radial ICP characteristics for ICP-AES using direct injection or microconcentric nebulisation2005In: Journal of Analytical Atomic Spectrometry, ISSN 0267-9477, E-ISSN 1364-5544, Vol. 20, no 7, p. 645-651Article in journal (Refereed)
    Abstract [en]

    Radial analyte signal intensities, fundamental plasma parameters, and non-spectral interference effects were characterized for inductively coupled plasma atomic emission spectrometry (ICP-AES) using a direct injection nebuliser (Vulkan DIN) or a microconcentric nebuliser (MCN) coupled to a cyclonic spray chamber for sample introduction. Radial analyte signal intensity profiles for atomic and ionic lines with energy sum (Esum) between 1.85 and 15.41 eV were used. When using the MCN system, for all lines the signal intensity profiles were parabolic with maxima at the axial centre of the plasma. For the Vulkan DIN, the shapes of the profiles were dependent on their Esum showing minimum intensities at the axial centre of the plasma for lines with high Esum values. The ionisation temperature, electron number density and magnesium ion-atom line intensity ratio determined indicated that ionisation and excitation capabilities were deteriorated at the centre of the plasma when using the Vulkan DIN compared with the MCN. This was found to be not simply a result of high aerosol load when using the Vulkan DIN, but because of poor plasma–aerosol interaction, possibly caused by the confined distribution of aerosol in the plasma and high nebuliser gas velocity. Indeed, for the Vulkan DIN, electron number density and ionisation temperature increased with liquid flow rate, which could be explained by plasma shrinkage, or the thermal pinch effect, which increased the aerosol–plasma interaction at increased liquid flow rates. As a consequence, when increasing the liquid flow rate in the range 20–90 µL min–1: (i) analyte sensitivity increased linearly; (ii) the plasma became unstable; (iii) the magnitude of matrix effects remained almost unaffected. These results are partly in contrast to observations made with other types of direct injection nebulisers and ICP instruments.

     

  • 23.
    Hakobyan, Shoghik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rzhepishevska, Olena
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ramstedt, Madeleine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Influence of Chelation Strength and Bacterial Uptake of Gallium Salicylidene Acylhydrazide on Biofilm Formation and Virulence by Pseudomonas aeruginosa2016In: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 160, p. 24-32Article in journal (Refereed)
    Abstract [en]

    Development of antibiotic resistance in bacteria causes major challenges for our society and has prompted a great need for new and alternative treatment methods for infection. One promising approach is to target bacterial virulence using for example salicylidene acylhydrazides (hydrazones). Hydrazones coordinate metal ions such as Fe(III) and Ga(III) through a five-membered and a six-membered chelation ring. One suggested mode of action is via restricting bacterial Fe uptake. Thus, it was hypothesized that the chelating strength of these substances could be used to predict their biological activity on bacterial cells. This was investigated by comparing Ga chelation strength of two hydrazone complexes, as well as bacterial Ga uptake, biofilm formation, and virulence in the form of production and secretion of a toxin (ExoS) by Pseudomonas aeruginosa. Equilibrium constants for deprotonation and Ga(III) binding of the hydrazone N′-(5-chloro-2-hydroxy-3-methylbenzylidene)-2,4-dihydroxybenzhydrazide (ME0329), with anti-virulence effect against P. aeruginosa, were determined and compared to bacterial siderophores and the previously described Ga(III) 2-oxo-2-[N-(2,4,6-trihydroxy-benzylidene)-hydrazino]-acetamide (Ga-ME0163) and Ga-citrate complexes. In comparison with these two complexes, it was shown that the uptake of Ga(III) was higher from the Ga-ME0329 complex. The results further show that the Ga-ME0329 complex reduced ExoS expression and secretion to a higher extent than Ga-citrate, Ga-ME0163 or the non-coordinated hydrazone. However, the effect against biofilm formation by P. aeruginosa, by the ME0329 complex, was similar to Ga-citrate and lower than what has been reported for Ga-ME0163.

  • 24. Havarinasab, S
    et al.
    Häggqvist, B
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Pollard, KM
    Hultman, P
    Immunosuppressive and autoimmune effects of thimerosal in mice2005In: TOXICOLOGY AND APPLIED PHARMACOLOGY, ISSN 0041-008X, Vol. 204, no 2, p. 109-21Article in journal (Refereed)
    Abstract [en]

    The possible health effects of the organic mercury compound thimerosal (ethylmercurithiosalicylate), which is rapidly metabolized to ethylmercury (EtHg), have recently been much debated and the effect of this compound on the immune system is largely unknown. We therefore studied the effect of thimerosal by treating A.SW (H-2(s)) mice, susceptible to induction of autoimmunity by heavy metals, with 10 mg thimerosal/L drinking water (internal dose ca 590 mu g Hg/kg body weight/day) for up to 30 days. The lymph node expression of IL-2 and IL-15 mRNA was increased after 2 days, and of IL-4 and IFN-gamma rnRNA after 6 and 14 days. During the first 14 days treatment, the number of splenocytes, including T and B cells as well as Ig-secreting cells decreased. A strong immunostimulation superseded after 30 days treatment xvith increase in splenic weight, number of splenocytes including T and B cells and Ig-secreting cells, and Th2- as well as Th-l-dependent serum immunoglobulins. Antinucleolar antibodies (ANoA) targeting the 34-kDa nucleolar protein fibrillarin, and systemic immune-complex deposits developed. The H-2(s) strains SJL and B10.S also responded to thimerosal treatment with ANoA. The A.TL and B10.TL strain, sharing background genes with the A.SW and B10.S strain, respectively, but with a different H-2 haplotype (tl), did not develop ANoA, linking the susceptibility to H-2. Thimerosal-treated H-2(s) mice homozygous for the nu mutation (SJL-nu/nu), or lacking the T-cell costimulatory molecule CD28 (B10.S-CD28(-/-)), did not develop ANoA, which showed that the autoimmune response is T-cell dependent. Using H-2(s) strains with targeted mutations, we found that IFN-gamma and IL-6, but not IL-4, is important for induction of ANoA by thimerosal. The maximum added renal concentration of thimerosal (EtHg) and inorganic mercury occurred after 14 days treatment and was 8 1 mu g Hg/g. EtHg made tip 59% and inorganic mercury 41% of the renal mercury. In conclusion, the organic mercury compound thimerosal (EtHg) has initial immunosuppressive effects similar to those of MeHg. However, in contrast to MeHg, thimerosal treatment leads in genetically susceptible mice to a second phase with strong immunostimulation and autoimmunity, which is T-cell dependent, H-2 linked and may at least partly be due to the inorganic mercury derived from the metabolism of ethyl mercury.

  • 25. Havarinasab, Said
    et al.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Ekstrand, Jimmy
    Hultman, Per
    Dose and Hg species determine the T-helper cell activation in murine autoimmunity.2007In: Toxicology, ISSN 0300-483X, Vol. 229, no 1-2, p. 23-32Article in journal (Refereed)
    Abstract [en]

    Inorganic mercury (mercuric chloride--HgCl(2)) induces in mice an autoimmune syndrome (HgIA) with T cell-dependent polyclonal B cell activation and hypergammaglobulinemia, dose- and H-2-dependent production of autoantibodies targeting the 34 kDa nucleolar protein fibrillarin (AFA), and systemic immune-complex deposits. The organic mercury species methylmercury (MeHg) and ethylmercury (EtHg--in the form of thimerosal) induce AFA, while the other manifestations of HgIA seen after treatment with HgCl(2) are present to varying extent. Since these organic Hg species are converted to the autoimmunogen Hg(2+) in the body, their primary autoimmunogen potential is uncertain and the subject of this study. A moderate dose of HgCl(2) (8 mg/L drinking water--internal dose 148 micro gHg/kg body weight [bw]/day) caused the fastest AFA response, while the induction was delayed after higher (25 mg/L) and lower (1.5 and 3 mg/L) doses. The lowest dose of HgCl(2) inducing AFA was 1.5 mg/L drinking water which corresponded to a renal Hg(2+) concentration of 0.53 micro g/g. Using a dose of 8 mg HgCl(2)/L this threshold concentration was reached within 24 h, and a consistent AFA response developed after 8-10 days. The time lag for the immunological part of the reaction leading to a consistent AFA response was therefore 7-9 days. A dose of thimerosal close to the threshold dose for induction of AFA (2 mg/L drinking water--internal dose 118 micro gHg/kg bw per day), caused a renal Hg(2+) concentration of 1.8 micro g/g. The autoimmunogen effect of EtHg might therefore be entirely due to Hg(2+) formed from EtHg in the body. The effect of organic and inorganic Hg species on T-helper type 1 and type 2 cells during induction of AFA was assessed as the presence and titre of AFA of the IgG1 and IgG2a isotype, respectively. EtHg induced a persistent Th1-skewed response irrespectively of the dose and time used. A low daily dose of HgCl(2) (1.5-3 mg/L) caused a Th1-skewed AFA response, while a moderate dose (8 mg/L) after 2 weeks resulted in a balanced or even Th2-skewed response. Higher daily doses of HgCl(2) (25 mg/L) caused a balanced Th2-Th1 response already from onset. In conclusion, while metabolically formed Hg(2+) might be the main AFA-inducing factor also after treatment with EtHg, the quality of the Hg-induced AFA response is modified by the species of Hg as well as the dose.

  • 26. Havarinasab, Said
    et al.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nielsen, Jesper B
    Hultman, Per
    Mercury species in lymphoid and non-lymphoid tissues after exposure to methyl mercury: Correlation with autoimmune parameters during and after treatment in susceptible mice2007In: Toxicology and Applied Pharmacology, Vol. 221, no 1, p. 21-8Article in journal (Refereed)
    Abstract [en]

    Methylmercury (MeHg) is present in the environment as a result of the global cycling of mercury, although anthropogenic sources may dramatically increase the availability in confined geographical areas. Accumulation of MeHg in the aquatic food chain is the dominating way of exposure in mammals, which accumulate MeHg in all organs, including the brain. Demethylation has been described in the organs, especially in phagocytic cells, but mainly in the flora of the intestinal tract. While most of the inorganic mercury (Hg2+) formed in the intestine is excreted, a fraction is reabsorbed which together with the local demethylation increases the organ Hg2+ concentration. MeHg is a well-known immunosuppressive agent, while Hg2+ is associated with immunostimulation and autoimmunity especially in genetically susceptible rodents, creating a syndrome, i.e. mercury-induced autoimmunity (HgIA). This study aimed at exploring the effect of MeHg with regard to HgIA, and especially the immunological events after stopping treatment, correlated with the presence of MeHg and Hg2+ in the organs.

    Treatment of A.SW mice for 30 days with 4.2 mg MeHg/L drinking water (corresponding to approximately 420 μg Hg/kg body weight/day) caused all the HgIA features observed after primary treatment with inorganic Hg, except systemic immune complex deposits. The total Hg concentration was 5-fold higher in the kidneys as compared with lymph nodes, but the fraction of Hg2+ was similar (17–20%). After stopping treatment, the renal and lymph node MeHg concentration declined according to first order kinetics during the initial 4–6 weeks, but then slower. A similar decline in the organ Hg2+ concentration occurred during the initial 2 weeks after stopping treatment but then ceased, causing the Hg2+ concentration to exceed that of MeHg in the lymph nodes and kidneys after 3 and 8 weeks, respectively. The selective increase in lymph node Hg2+ fraction is likely to be due to demethylation of MeHg in the macrophage-rich lymphoid tissue. The major autoantibody in HgIA, anti-fibrillarin antibodies, tended to increase during the initial 6 weeks after stopping treatment, while all other HgIA features including antichromatin antibodies declined to control levels after 2–4 weeks. This indicates differences in either dose requirement or induction mechanisms for the different HgIA parameters.

    The selective accumulation of Hg2+ in lymph nodes following MeHg treatment should be taken into account when the effect of MeHg on the immune system is evaluated.

  • 27.
    Hemström, Petrus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nygren, Yvonne
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Alternative organic solvents for HILIC separation of cisplatin species with on-line ICP-MS detection2008In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 31, no 4, p. 599-603Article in journal (Refereed)
    Abstract [en]

    Several low volatile organic solvents were evaluated as organic modifiers in eluents for HILIC separations of cisplatin species to optimize the on-line coupling of HILIC to inductively coupled plasma MS (ICP-MS). The aim was to identify a solvent giving low solvent vapor loading of the ICP, to maximize analyte sensitivity and minimize carbon depositions on instrumental parts, while retaining chromatographic performance. The best overall performance of the HILIC-ICP-MS system for the analysis of cisplatin was achieved using 1,4-dioxane as eluent, yielding high retention and an HILIC type retention mechanism, at the expense of a 50% drop in column efficiency due to the higher viscosity of 1,4-dioxane compared to the more commonly used HILIC solvent ACN. Using 1,4-dioxane as solvent in HILIC provides the best compromise between carbon deposition and separation efficiency among a series of high-boiling water-miscible solvents tested.

  • 28. Hermann, G
    et al.
    Trenin, A
    Matz, R
    Gafurov, M
    Gilmutdinov, A Kh
    Nagulin, K Yu
    Frech, Wolfgang
    Umeå University, Faculty of Science and Technology, Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Grinshtein, I
    Vasilieva, L
    Platform-to-platform sample transfer, distribution, dilution, and dosing via electrothermal vaporization and electrostatic deposition2004In: Spectrochimica Acta Part B: Atomic Spectroscopy, Vol. 59, no 5, p. 737-48Article in journal (Refereed)
    Abstract [en]

    A novel system for solid sample pretreatment, handling and dosing for analytical atomic spectrometry is described. A primary solid or liquid sample is vaporized in a graphite furnace and then condensed in a specially designed condensation zone. On the further transport path, the analyte aerosol can be diluted and distributed in pre-set ratios in the laboratory made flow control system. Applying a corona discharge, aerosol particulates are then quantitatively re-collected by means of intra-furnace electrostatic precipitation on the platform of another graphite furnace or by external precipitation on one or a set of platforms. This makes possible to produce a set of secondary platforms with equal analyte compositions from one individual primary sample. Such multitudes allow sequential multi-element determinations with single-element instrumentation or comparative measurements with different techniques. Furthermore, the described procedure allows external thermal sample pretreatment with preceding pyrolysis and additional vaporization, condensation, and re-precipitation that significantly reduces or removes the sample matrix. Owing to different losses, transport efficiencies of electrothermal vaporization (ETV) instrumentation depend on analyte element, matrix, vaporization temperature, ramp rate, and tube history. In order to reduce the losses and therewith such dependencies of the losses, new laboratory constructed ETV unit with analyte condensation in an axially focusing upstream convection zone has been constructed. Analytical performance of the new setup is compared with the performance of a commercial end-on flow-through ETV unit when analyzing both liquid dosed samples and certified solid reference materials. The new system shows much higher transport efficiencies that are, in addition, more uniform for elements of different volatility. The effects of chemical sample modifiers and elements supporting analyte condensation are studied. Most of the analytical measurements were carried out with a continuum source coherent forward scattering multi-element spectrometer. Comparative measurements were also carried out independently in the co-authors’ laboratories with atomic absorption and inductively coupled plasma mass spectrometry techniques.

  • 29. Herrero Ortega, Sonia
    et al.
    Catalan, Núria
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gröntoft, Hannes
    Hilmarsson, Torfi Geir
    Bertilsson, Stefan
    Wu, Pianpian
    Bishop, Kevin
    Levanoni, Oded
    Bravo, Andrea G.
    High methylmercury formation in ponds fueled by fresh humic and algal derived organic matter2018In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, p. S44-S53Article in journal (Refereed)
    Abstract [en]

    Neurotoxic methylmercury causes adverse effects to ecosystem viability and human health. Previous studies have revealed that ponding alters natural organic matter (NOM) composition and increase methylmercury concentrations in rivers, especially in the first years after flooding. Here, we investigate the influence of NOM composition (i.e., sources and degradation status) on mercury methylation rate constants in nine boreal beaver ponds of different ages across Sweden. We show that increased methylmercury concentrations in surface waters is a consequence of enhanced mercury methylation in the pond sediments. Moreover, our results reveal that during the first years after the initial flooding, mercury methylation rates are fueled by the amount of fresh humic substances released from the flooded soils and by an increased production of algal-derived NOM triggered by enhanced nutrient availability. Our findings indicate that impoundment-induced changes in NOM composition control mercury methylation processes, causing the raise in MeHg levels in ponds.

  • 30. Häggqvist, Bo
    et al.
    Havarinasab, Said
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Hultman, Per
    The immunosuppressive effect of methylmercury does not preclude development of autoimmunity in genetically susceptible mice2005In: TOXICOLOGY, ISSN 0300-483X, Vol. 208, no 1, p. 149-64Article in journal (Refereed)
    Abstract [en]

    Methylmercury (MeHg) is a common environmental pollutant due to both natural and anthropogenic sources. Although the central nervous system (CNS) is considered the critical organ for the toxic effect of MeHg, it has recently been suggested that the immune system might be at least as sensitive as the CNS.

    We have examined the effects of MeHg on the immune system in genetically metal-susceptible mice. Subcutaneous (sc) injections of 2 mg MeHg/kg body weight (bw) every third day (internal dose ca. 540 μg Hg/kg bw/day) to A.SW mice of the H-2s haplotype, caused during the first week a 47 and 9% reduction of B- and T-cells, respectively, which indicates immunosuppression. Subsequently, an autoimmune syndrome developed which shared certain features with the syndrome induced by inorganic mercury in H-2s mice, including antibodies targeting the 34 kDa nucleolar protein fibrillarin, increased expression of IL-4 mRNA, increase of Th2-type of immunoglobulins (IgE and IgG1), and increased MHC class II expression on B-cells. However, the response using MeHg was attenuated compared with even lower doses of Hg in the form of inorganic mercury, and specifically lacked the increased expression of IL-2 and IFN-γ mRNA, the polyclonal B-cell activation (PBA), and the systemic immune-complex (IC) deposits which are induced by inorganic mercury. Increasing the dose of MeHg increased the titre of anti-nucleolar antibodies and shortened the induction time, but did not lead to stronger immunostimulation or systemic IC-deposits. The kidney and liver selectively accumulated MeHg, while the blood, spleen and lymph nodes showed lower levels of MeHg. The accumulation of MeHg and Hg2+ increased throughout the 30-day period. The fraction of Hg2+ in the kidney varied between 4 and 22%, and the lymph nodes showed a maximum of 30% Hg2+.

    We conclude first that MeHg has quantitatively different effect on the immune system compared with inorganic mercury, and secondly that an initial immunosuppression induced by a xenobiotic does not preclude subsequent immunostimulation and autoimmunity.

  • 31. Isidorova, Anastasija
    et al.
    Bravo, Andrea G.
    Riise, Gunnhild
    Bouchet, Sylvain
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sobek, Sebastian
    The effect of lake browning and respiration mode on the burial and fate of carbon and mercury in the sediment of two boreal lakes2016In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 121, no 1, p. 233-245Article in journal (Refereed)
    Abstract [en]

    In many northern temperate regions, the water color of lakes has increased over the past decades (lake browning), probably caused by an increased export of dissolved organic matter from soils. We investigated if the increase in water color in two lakes in Norway has resulted in increased burial of organic carbon (OC) and mercury (Hg) in the sediments and if the Hg was prone to methylation. Lake Solbergvann experienced a threefold water color increase, and OC burial increased approximately twofold concomitant to the water color increase. This lake had prolonged periods of anoxic bottom water, and anoxic OC mineralization rates were only about half of the oxic OC mineralization rates (7.7 and 17.5g C m(-2)yr(-1), respectively), contributing to an efficient OC burial. In Lake Elvaga, where water color increase was only approximately twofold and bottom water was oxygenated, no recent increase in OC burial could be observed. Hg burial increased strongly in both lakes (threefold and 1.6-fold in Lake Solbergvann and Lake Elvaga, respectively), again concomitant to the recent water color increase. The proportion of methylated Hg (MeHg) in surficial sediment was 1 order of magnitude higher in Lake Elvaga (up to 6% MeHg) than in Lake Solbergvann (0.2-0.6% MeHg), probably related to the different oxygenation regimes. We conclude that lake browning can result in increased OC and Hg burial in lake sediments, but the extent of browning and the dominating mode of sediment respiration (aerobic or anaerobic) strongly affect burial and fate of OC and Hg in sediments.

  • 32. Jiang, Tao
    et al.
    Bravo, Andrea G.
    Skyllberg, Ulf
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wang, Dingyong
    Yan, Haiyu
    Green, Nelson W.
    Influence of dissolved organic matter (DOM) characteristics on dissolved mercury (Hg) species composition in sediment porewater of lakes from southwest China2018In: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, Vol. 146, p. 146-158Article in journal (Refereed)
    Abstract [en]

    The origin and composition of dissolved organic matter (DOM) in porewater of lake sediments is intricate and decisive for fate of pollutants including mercury (Hg). While there are many reports on the relationship between dissolved organic carbon concentration (DOC) and mercury (Hg) concentrations in aquatic systems, there are few in which DOM compositional properties, that may better explain the fate of Hg, have been the focus. In this study, porewaters from sediments of three lakes, Caihai Lake (CH), Hongfeng Lake (HF) and Wujiangdu Lake (WJD), all located in southwest China, were selected to test the hypothesis that DOM optical properties control the fate of Hg in aquatic ecosystems. Porewater DOM was extracted and characterized by UV-Vis absorption and fluorescence spectroscopy. A two end-member (autochthonous and allochthonous DOM) mixing model was used to unveil the origin of DOM in porewaters of the three lakes. Our results show a higher input of terrestrial DOM in the pristine lake CH, as compared to lakes HF and WJD lakes, which were both influenced by urban environments and enriched in autochthonous DOM. While the relationships between the concentrations of DOC and the different chemical forms of Hg forms were quite inconsistent, we found important links between specific DOM components and the fate of Hg in the three lakes. In particular, our results suggest that allochthonous, terrestrial DOM inhibits Hg(II) availability for Hg methylating micro-organisms. In contrast, autochthonous DOM seems to have been stimulated MeHg formation, likely by enhancing the activity of microbial communities. Indeed, DOM biodegradation experiments revealed that differences in the microbial activity could explain the variation in the concentration of MeHg. While relationships between concentrations of DOC and Hg vary among different sites and provide little information about Hg cycling, we conclude that the transport and transformation of Hg (e.g. the methylation process) are more strongly linked to DOM chemical composition and reactivity.

  • 33. Jiang, Tao
    et al.
    Skyllberg, Ulf
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Green, Nelson W.
    Tang, Jianhui
    Wang, Dingyong
    Gao, Jie
    Li, Chuxian
    Characteristics of dissolved organic matter (DOM) and relationship with dissolved mercury in Xiaoqing River-Laizhou Bay estuary, Bohai Sea, China2017In: Environmental Pollution, ISSN 0269-7491, E-ISSN 1873-6424, Vol. 223, p. 19-30Article in journal (Refereed)
    Abstract [en]

    Abstract Because of heterogeneous properties, dissolved organic matter (DOM) is known to control the environmental fate of a variety of organic pollutants and trace metals in aquatic systems. Here we report absorptive and fluorescence properties of DOM, in concurrence with concentrations of dissolved mercury (Hg), along the Xiaoqing River-Laizhou Bay estuary system located in the Bohai Sea of China. A mixing model consisting of the two end-members terrestrial and aquatic DOM demonstrated that terrestrial signatures decreased significantly from the river into the estuary. Quasi-conservative mixing behavior of DOM sources suggests that the variations in the average DOM composition were governed by physical processes (e.g., dilution) rather than by new production and/or degradation processes. In contrast to some previous studies of river-estuary systems, the Xiaoqing River-Laizhou Bay estuary system displayed a non-significant correlation between DOM and Hg quantities. Based on this and the variation of Hg concentration along the salinity gradient, we concluded that Hg showed a non-conservative mixing behavior of suggested end-member sources. Thus, rather than mixing, Hg concentration variations seemed to be controlled by biogeochemical processes.

  • 34.
    Jiskra, Martin
    et al.
    Soil Chemistry, Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zurich.
    Saile, Damian
    Soil Chemistry, Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zurich.
    Wiederhold, Jan G.
    Soil Chemistry, Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zurich.
    Bourdon, Bernard
    Laboratoire de Géologie de Lyon, ENS Lyon, France.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Kretzschmar, Ruben
    Soil Chemistry, Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zurich.
    Kinetics of Hg(II) Exchange between Organic Ligands, Goethite, and Natural Organic Matter Studied with an Enriched Stable Isotope Approach2014In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 48, no 22, p. 13207-13217Article in journal (Refereed)
    Abstract [en]

    The mobility and bioavailability of toxic Hg(II) in the environment strongly depends on its interactions with natural organic matter (NOM) and mineral surfaces. Using an enriched stable isotope approach, we investigated the exchange of Hg(II) between dissolved species (inorganically complexed or cysteine-,EDTA-, or NOM-bound) and solid-bound Hg(II) (carboxyl-/thiol-resin or goethite) over 30 days under constant conditions (pH, Hg and ligand concentrations). The Hg(II)-exchange was initially fast, followed by a slower phase, and depended on the properties of the dissolved ligands and sorbents. The results were described by a kinetic model allowing the simultaneous determination of adsorption and desorption rate coefficients. The time scales required to reach equilibrium with the carboxylresin varied greatly from 1.2 days for Hg(OH)(2) to 16 days for Hg(II) cysteine complexes and approximately 250 days for EDTA-bound Hg(10. Other experiments could not be described by an equilibrium model, suggesting that a significant fraction of total-bound Hg was present in a non-exchangeable form (thiol-resin and NOM: 53-58%; goethite: 22-29%). Based on the slow and incomplete exchange of Hg(II) described in this study, we suggest that kinetic effects must be considered to a greater extent in the assessment of the fate of Hg in the environment and the design of experimental studies, for example, for stability constant determination or metal isotope fractionation during sorption.

  • 35.
    Jonsson, Sofi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Mats B
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences.
    Skyllberg, Ulf
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences.
    Lundberg, Erik
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Schaefer, Jeffra K
    Department of Geosciences, Princeton University.
    Åkerblom, Staffan
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Impact of nutrient and humic matter loadings on methylmercury formation and bioaccumulation in estuarine ecosystemsManuscript (preprint) (Other academic)
  • 36.
    Jonsson, Sofi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Mats B.
    Skyllberg, Ulf
    Lundberg, Erik
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Schaefer, Jeffra K.
    Åkerblom, Staffan
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Terrestrial discharges mediate trophic shifts and enhance methylmercury accumulation in estuarine biota2017In: Science Advances, Vol. 3, no 1, article id e1601239Article in journal (Refereed)
    Abstract [en]

    The input of mercury (Hg) to ecosystems is estimated to have increased two- to fivefold during the industrial era, and Hg accumulates in aquatic biota as neurotoxic methylmercury (MeHg). Escalating anthropogenic land use and climate change are expected to alter the input rates of terrestrial natural organic matter (NOM) and nutrients to aquatic ecosystems. For example, climate change has been projected to induce 10 to 50% runoff increases for large coastal regions globally. A major knowledge gap is the potential effects on MeHg exposure to biota following these ecosystem changes. We monitored the fate of five enriched Hg isotope tracers added to mesocosm scale estuarine model ecosystems subjected to varying loading rates of nutrients and terrestrial NOM. We demonstrate that increased terrestrial NOM input to the pelagic zone can enhance the MeHg bioaccumulation factor in zooplankton by a factor of 2 to 7 by inducing a shift in the pelagic food web from autotrophic to heterotrophic. The terrestrial NOM input also enhanced the retention of MeHg in the water column by up to a factor of 2, resulting in further increased MeHg exposure to pelagic biota. Using mercury mass balance calculations, we predict that MeHg concentration in zooplankton can increase by a factor of 3 to 6 in coastal areas following scenarios with 15 to 30% increased terrestrial runoff. The results demonstrate the importance of incorporating the impact of climate-induced changes in food web structure on MeHg bioaccumulation in future biogeochemical cycling models and risk assessments of Hg.

  • 37.
    Jonsson, Sofi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Swedish University of Agricultural Sciences.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Substantial emission of gaseous monomethylmercury from contaminated water-sediment microcosms2010In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 44, no 1, p. 278-283Article in journal (Refereed)
    Abstract [en]

    Emission rates of gaseous monomethylmercury (CH(3)Hg(II)), as well as elemental mercury (Hg(0)) and dimethylmercury [(CH(3))(2)Hg(II)], were determined in Hg-contaminated water-sediment microcosms (duplicates of three treatments) by gaseous species-specific isotope dilution analysis (SSIDA). Incubation of approximately 500 g (wet mass) of sediments containing 30 mumol of ambient Hg with an addition of 2.6 mumol of (201)Hg(II) tracer resulted in average (n = 6) gaseous emissions of 84 +/- 26, 100 +/- 37, and 830 +/- 380 pmol of ambient CH(3)Hg(II), CH(3)(201)Hg(II), and (201)Hg(0), respectively, during 108 days of incubation. In contrast to Hg(0), a transient temporal pattern was observed for measured CH(3)Hg(II) emission rates, which peaked at day 12 and decreased to much lower levels by the end of the experiments. At day 12, CH(3)Hg(II) constituted 30-50% of the total emitted gaseous Hg, emphasizing the significance of this species to total Hg emissions from anoxic sediment-water systems. Emission rates of gaseous CH(3)Hg(II) did not reflect the accumulated CH(3)Hg(II) content in the sediment, suggesting that emissions mainly originated from newly methylated Hg(II). Speciation modeling of the pore water suggests that CH(3)Hg(II) was emitted as CH(3)HgSH(0)(g).

  • 38.
    Jonsson, Sofi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Nilsson, Mats B.
    Lundberg, Erik
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Differentiated availability of geochemical mercury pools controls methylmercury levels in estuarine sediment and biota2014In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, p. 4624-Article in journal (Refereed)
    Abstract [en]

    Neurotoxic methylmercury (MeHg) formed from inorganic divalent mercury (HgII) accumulates in aquatic biota and remains at high levels worldwide. It is poorly understood to what extent different geochemical Hg pools contribute to these levels. Here we report quantitative data on MeHg formation and bioaccumulation, in mesocosm water-sediment model ecosystems, using five HgII and MeHg isotope tracers simulating recent Hg inputs to the water phase and Hg stored in sediment as bound to natural organic matter or as metacinnabar. Calculations for an estuarine ecosystem suggest that the chemical speciation of HgII solid/adsorbed phases control the sediment Hg pool's contribution to MeHg, but that input of MeHg from terrestrial and atmospheric sources bioaccumulates to a substantially greater extent than MeHg formed in situ in sediment. Our findings emphasize the importance of MeHg loadings from catchment runoff to MeHg content in estuarine biota and we suggest that this contribution has been underestimated.

  • 39.
    Jonsson, Sofi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences.
    Nilsson, Mats B
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences.
    Lundberg, Erik
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Differentiated reactivity of geochemical mercury pools control methylmercury levels in sediment and biotaManuscript (preprint) (Other academic)
  • 40.
    Jonsson, Sofi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Nilsson, Mats B
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Westlund, Per-Olof
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lundberg, Erik
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mercury methylation rates for geochemically relevant HgII species in sediments2012In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 46, no 21, p. 11653-11659Article in journal (Refereed)
    Abstract [en]

    Monomethylmercury (MeHg) in fish from freshwater, estuarine and marine environments are a major global environmental issue. Mercury levels in biota are mainly controlled by the methylation of inorganic mercuric mercury (HgII) to MeHg in water, sediments and soils. There is, however, a knowledge gap concerning the mechanisms and rates of methylation of specific geochemical HgII species. Such information is crucial for a better understanding of variations in MeHg concentrations among ecosystems and, in particular, for predicting the outcome of currently proposed measures to mitigate mercury emissions and reduce MeHg concentrations in fish. To fill this knowledge gap we propose an experimental approach using HgII isotope tracers, with defined and geochemically important adsorbed and solid HgII forms in sediments, to study MeHg formation. We report HgII methylation rate constants, km, in estuarine sediments which span over two orders of magnitude depending on chemical form of added tracer: metacinnabar (β-201HgS(s)) < cinnabar (α-199HgS(s)) < HgII reacted with mackinawite (≡FeS-202HgII) < HgII bonded to natural organic matter (NOM-196HgII) < a typical aqueous tracer (198Hg(NO3)2(aq)). We conclude that a combination of thermodynamic and kinetic effects of HgII solid-phase dissolution and surface desorption control the HgII methylation rate in sediments and causes the large observed differences in km-values. The selection of relevant solid-phase and surface adsorbed HgII tracers will therefore be crucial to achieving biogeochemically accurate estimates of ambient HgII methylation rates.

  • 41. Karlsson, Torbjörn
    et al.
    Elgh-Dalgren, Kristin
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Skyllberg, Ulf
    Complexation of cadmium to sulfur and oxygen functional groups in an organic soil2007In: Geochimica et Cosmochimica Acta, Vol. 71, p. 604-14Article in journal (Refereed)
    Abstract [en]

    Cadmium (Cd) is a toxic trace element and due to human activities soils and waters are contaminated by Cd both on a local and global scale. It is widely accepted that chemical interactions with functional groups of natural organic matter (NOM) is vital for the bioavailability and mobility of trace elements. In this study the binding strength of cadmium (Cd) to soil organic matter (SOM) was determined in an organic (49% organic C) soil as a function of reaction time, pH and Cd concentration. In experiments conducted at native Cd concentrations in soil (0.23 μg g−1 dry soil), halides (Cl, Br) were used as competing ligands to functional groups in SOM. The concentration of Cd in the aqueous phase was determined by isotope-dilution (ID) inductively-coupled-plasma-mass-spectrometry (ICP-MS), and the activity of Cd2+ was calculated from the well-established Cd–halide constants. At higher Cd loading (500–54,000 μg g−1), the Cd2+ activity was directly determined by an ion-selective electrode (ISE). On the basis of results from extended X-ray absorption fine structure (EXAFS) spectroscopy, a model with one thiolate group (RS−) was used to describe the complexation (Cd2+ + RS− two left arrows CdSR+; log KCdSR) at native Cd concentrations. The concentration of thiols (RSH; 0.047 mol kg−1 C) was independently determined by X-ray absorption near-edge structure (XANES) spectroscopy. Log KCdSR values of 11.2–11.6 (pKa for RSH = 9.96), determined in the pH range 3.1–4.6, compare favorably with stability constants for the association between Cd and well-defined thiolates like glutathione. In the concentration range 500–54,000 μg Cd g−1, a model consisting of one thiolate and one carboxylate (RCOO−) gave the best fit to data, indicating an increasing role for RCOOH groups as RSH groups become saturated. The determined log KCdOOCR of 3.2 (Cd2+ + RCOO− two left arrows CdOOCR+; log KCdOOCR; pKa for RCOOH = 4.5) is in accordance with stability constants determined for the association between Cd and well-defined carboxylates. Given a concentration of reduced sulfur groups of 0.2% or higher in NOM, we conclude that the complexation to organic RSH groups may control the speciation of Cd in soils, and most likely also in surface waters, with a total concentration less than 5 mg Cd g−1 organic C.

  • 42.
    Kozyatnyk, Ivan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bouchet, Sylvain
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Haglund, Peter
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Fractionation and size-distribution of metal and metalloid contaminants in a polluted groundwater rich in dissolved organic matter2016In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 318, p. 194-202Article in journal (Refereed)
    Abstract [en]

    We investigated the concentration levels, fractionation and molecular weight distribution (MWD) of dissolved organic matter (DOM) and metals (V, Cr, Co, Ni, Cu, Zn, As, Cd, Sn, Ba, Hg and Pb) in a polluted groundwater from an industrial area in Northern Sweden. DOM was mainly recovered in the hydrophobic acidic and hydrophobic neutral sub-fractions (45 and 35%, respectively) while most metals were found in the acidic sub-fractions (46–93%) except for V, Fe and As, which were predominant in the basic sub-fractions (74–93%) and Cd in the neutral ones (50%). DOM exhibited a broad MWD in groundwaters, usually from 5 to 200 kDa and was dominated by high molecular weight hydrophobic acids, low molecular weight hydrophilic acids and hydrophilic neutral compounds. Most of the studied metals (Fe, Cr, Co, Sn, Ba, Hg) were associated with the high molecular weight DOM fraction (ca. 40–100 kDa). Cu, Pb, Zn, Cd and Ni interacted with a broad range of DOM size fractions but were still most abundant in the high molecular weight fraction. Few metal/metalloids (As, V and Cr in some cases) presented a very weak affinity for DOM and presumably existed predominantly as “free” inorganic ions in solution.

  • 43. Kronberg, Rose-Marie
    et al.
    Drott, Andreas
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jiskra, Martin
    Wiederhold, Jan G.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Forest harvest contribution to Boreal freshwater methyl mercury load2016In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 30, no 6, p. 825-843Article in journal (Refereed)
    Abstract [en]

    Effects of Boreal forest harvest on mercury (Hg) and methyl mercury (MeHg) soil pools and export by stream runoff were quantified by comparing 10 reference watersheds (REFs) covered by >80year old Norway spruce (Picea abies Karst.) forests with 10 similar watersheds subjected to clear-cutting (CCs). While total Hg soil storage did not change, MeHg pools increased seven times (p=0.006) in the organic topsoil 2 years after clear-cutting. In undulating terrain, situated above the postglacial marine limit (ML) of the ancient Baltic Sea, the mass ratio between flux-weighted MeHg and dissolved organic carbon (MeHg/DOC) in stream runoff increased 1.8 times (p<0.004) as a consequence of forest harvest. When recalculated to 100% clear-cutting of the watershed, the annual MeHg stream export increased 3.8 times (p=0.047). Below the ML, where the terrain was flatter, neither the MeHg/DOC ratio nor the annual export of MeHg differed between REFs and CCs, likely because of the larger contribution of MeHg exported from peaty soils and small wetlands. The most robust measure, MeHg/DOC, was used to calculate MeHg loadings to Boreal headwaters. If the forest harvest effect lasts 10years, clear-cutting increases MeHg runoff by 12-20% in Sweden and 2% in the Boreal zone as a whole. In Sweden, having intensely managed forests, 37% and 56% of MeHg are exported from peatlands and forest soils, respectively, and forest clear-cutting is adding another 6.6%. In the Boreal zone as a whole peatlands and forests soils contribute with 53% and 46%, respectively, and clear-cutting is estimated to add another 1.0%. An expected rapid increase in Boreal forest harvest and disturbance urge for inclusion of land use effects in mercury biogeochemical cycling models at different scales.

  • 44. Kronberg, Rose-Marie
    et al.
    Jiskra, Martin
    Weiderhold, Jan. G
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Methyl Mercury Formation in Hillslope Soils of Boreal Forests: the Role of Forest Harvest and Anaerobic Microbes2016In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 50, no 17, p. 9177-9186Article in journal (Refereed)
    Abstract [en]

    Final harvest (clear-cutting) of coniferous boreal forests has been shown to increase streamwater concentrations andexport of the neurotoxin methyl mercury (MeHg) to freshwater ecosystems. Here, the spatial distribution of inorganic Hg and MeHgin soil as a consequence of clear-cutting is reported. A comparison ofsoils at similar positions along hillslopes in four 80 years old Norwayspruce (Picea abies) stands (REFs) with those in four similar stands subjected to clear-cutting (CCs) revealed significantly (p < 0.05)enhanced MeHg concentrations (ng g−1), MeHg areal masses (gha−1), and percent MeHg of HgTOT in O horizons of CCs locatedbetween 1 and 41 m from streams. Inorganic Hg measures did notdiffer between REFs and CCs at any position. The O horizon thickness did not differ between CCs and REFs, but the groundwater table and soil water content were significantly higher at CCs than at REFs. The largest difference in percent MeHg of HgTOT (12times higher at CCs compared to REFs, p = 0.003) was observed in concert with a significant enhancement in soil water content(p = 0.0003) at intermediate hillslope positions (20−38 m from stream), outside the stream riparian zone. Incubationexperiments demonstrated that soils having significantly enhanced soil pools of MeHg after clear-cutting also showed significantlyenhanced methylation potential as compared with similarly positioned soils in mature reference stands. The addition of inhibitorsdemonstrated that sulfate-reducing bacteria (SRB) and methanogens were key methylators. Rates of demethylation did not differbetween CCs and REFs. Our results suggest that enhanced water saturation of organic soils providing readily available electrondonors stimulate Hg-methylating microbes to net formation and buildup of MeHg in O horizons after forest harvest.

  • 45. Kronberg, Rose-Marie
    et al.
    Schaefer, Jeffra K.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Mechanisms of Methyl Mercury Net Degradation in Alder Swamps: The Role of Methanogens and Abiotic Processes2018In: Environmental Science and Technology Letters, E-ISSN 2328-8930, Vol. 5, no 4, p. 220-225Article in journal (Refereed)
    Abstract [en]

    Wetlands are common net producers of the neurotoxin monomethylmercury (MeHg) and are largely responsible for MeHg bioaccumulation in aquatic food-webs. However, not all wetlands net produce MeHg; notable exceptions are black alder (Alnus glutinosa) swamps, which net degrade MeHg. Here we report the mechanisms of MeHg demethylation in one such swamp (EHT), shown to be a sink for MeHg during four consecutive years. The potential demethylation rate constant (k(d) ) in soil incubations was similar to 3 times higher in the downstream (EHT-D: k(d) similar to 0.14 d(-1)) as compared to the upstream part of the swamp (EHT-U: k(d) 0.05 d(-1)). This difference concurred with increased stream and soil pH, and a change in plant community composition. Electron acceptor and inhibitor addition experiments revealed that abiotic demethylation dominated at EHT-U while an additional and equally large contribution from biotic degradation was observed at EHT-D, explaining the increase in MeHg degradation. Biotic demethylation (EHT-D) was primarily due to methanogens, inferred by a decrease in k(d) to autoclaved levels following selective inhibition of methanogens. Though methanogen-specific transcripts (mcrA) were found throughout the wetland, transcripts clustering with Methanosaetaceae were exclusive to EHT-D, suggesting a possible role for these acetoclastic methanogens in the degradation of MeHg.

  • 46. Kronberg, Rose-Marie
    et al.
    Tjerngren, Ida
    Drott, Andreas
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Net degradation of methyl mercury in alder swamps2012In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 46, no 24, p. 13144-13151Article in journal (Refereed)
    Abstract [en]

    Wetlands are generally considered to be sources of methyl mercury (MeHg) in northern temperate landscapes. However, a recent input-output mass balance study during 2007-2010 revealed a black alder (Alnus glutinosa) swamp in southern Sweden to be a consistent and significant MeHg sink, with a 30-60% loss of MeHg. The soil pool of MeHg varied substantially between years, but it always decreased with distance from the stream inlet to the swamp. The soil MeHg pool was significantly lower in the downstream as compared to the upstream half of the swamp (0.66 and 1.34 ng MeHg g(-1) SOC(-1) annual average(-1), respectively, one-way ANOVA, p = 0.0006). In 2008 a significant decrease of %MeHg in soil was paralleled by a significant increase in potential demethylation rate constant (k(d), p < 0.02 and p < 0.004, respectively). In contrast, the potential methylation rate constant (k(m)) was unrelated to distance (p = 0.3). Our results suggest that MeHg was net degraded in the Alnus swamp, and that it had a rapid and dynamic internal turnover of MeHg. Snapshot stream input-output measurements at eight additional Alnus glutinosa swamps in southern Sweden indicate that Alnus swamps in general are sinks for MeHg. Our findings have implications for forestry practices and landscape planning, and suggest that restored or preserved Alnus swamps may be used to mitigate MeHg produced in northern temperate landscapes.

  • 47. Kwong, Wai Ling
    et al.
    Lee, Cheng Choo
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Chemistry-Ångström Laboratory, Molecular Biomimetics, Uppsala University, 75120 Uppsala, Sweden.
    High-performance iron (III) oxide electrocatalyst for water oxidation in strongly acidic media2018In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 365, p. 29-35Article in journal (Refereed)
    Abstract [en]

    Stable and efficient oxygen evolution reaction (OER) catalysts for the oxidation of water to dioxygen in highly acidic media are currently limited to expensive noble metal (Ir and Ru) oxides since presently known OER catalysts made of inexpensive earth-abundant materials generally suffer anodic corrosion at low pH. In this study, we report that a mixed-polymorph film comprising maghemite and hematite, prepared using spray pyrolysis deposition followed by low-temperature annealing, showed a sustained OER rate (>24 h) corresponding to a current density of 10 mA cm−2 at an initial overpotential of 650 mV, with a Tafel slope of only 56 mV dec−1 and near-100% Faradaic efficiency in 0.5 M H2SO4 (pH 0.3). This performance is remarkable, since iron (III) oxide films comprising only maghemite were found to exhibit a comparable intrinsic activity, but considerably lower stability for OER, while films of pure hematite were OER-inactive. These results are explained by the differences in the polymorph crystal structures, which cause different electrical conductivity and surface interactions with water molecules and protons. Our findings not only reveal the potential of iron (III) oxide as acid-stable OER catalyst, but also highlight the important yet hitherto largely unexplored effect of crystal polymorphism on electrocatalytic OER performance.

  • 48.
    Lambertsson, Lars
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Validation of a simplified field-adapted procedure for routine determinations of methyl mercury at trace levels in natural water samples using species-specific isotope dilution mass spectrometry2004In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642 (Print) 1618-2650 (Online), Vol. 380, no 7-8, p. 871-5Article in journal (Refereed)
    Abstract [en]

    A field-adapted procedure based on species-specific isotope dilution (SSID) methodology for trace-level determinations of methyl mercury (CH3Hg+) in mire, fresh and sea water samples was developed, validated and applied in a field study. In the field study, mire water samples were filtered, standardised volumetrically with isotopically enriched CH3200Hg+, and frozen on dry ice. The samples were derivatised in the laboratory without further pre-treatment using sodium tetraethyl borate (NaB(C2H5)4) and the ethylated methyl mercury was purge-trapped on Tenax columns. The analyte was thermo-desorbed onto a GC-ICP-MS system for analysis. Investigations preceding field application of the method showed that when using SSID, for all tested matrices, identical results were obtained between samples that were freeze-preserved or analysed unpreserved. For DOC-rich samples (mire water) additional experiments showed no difference in CH3Hg+ concentration between samples that were derivatised without pre-treatment or after liquid extraction. Extractions of samples for matrix–analyte separation prior to derivatisation are therefore not necessary. No formation of CH3Hg+ was observed during sample storage and treatment when spiking samples with 198Hg2+. Total uncertainty budgets for the field application of the method showed that for analyte concentrations higher than 1.5 pg g–1 (as Hg) the relative expanded uncertainty (REU) was approximately 5% and dominated by the uncertainty in the isotope standard concentration. Below 0.5 pg g–1 (as Hg), the REU was >10% and dominated by variations in the field blank. The uncertainty of the method is sufficiently low to accurately determine CH3Hg+ concentrations at trace levels. The detection limit was determined to be 4 fg g–1 (as Hg) based on replicate analyses of laboratory blanks. The described procedure is reliable, considerably faster and simplified compared to non-SSID methods and thereby very suitable for routine applications of CH3Hg+ speciation analysis in a wide range of water samples.

  • 49.
    Lambertsson, Lars
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lord, Charles J.
    Frech, Wolfgang
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rapid dissolution of cinnabar in crude oils at reservoir temperatures facilitated by reduced Sulfur Ligands2018In: ACS Earth and Space Chemistry, ISSN 2472-3452, Vol. 2, no 10, p. 1022-1028Article in journal (Refereed)
    Abstract [en]

    Mercury (Hg) is present in petrochemical samples, including crude oils, and the processing and use of petroleum products contribute to global Hg emissions. We present a refined theory on geochemical processes controlling Hg concentrations in crude oil by studying dissolution kinetics and solubility thermodynamics of cinnabar (α-HgS(s)) in different crude oils held at reservoir temperatures. In a black light crude oil, α-HgS(s) dissolved in an apparent zero-order reaction with a rate of 0.14−0.58 μmoles m−2 s −1 at 170−230 °C and an estimated activation energy of 43 kJ mol−1 . For crude oil samples with a total sulfur concentration spanning 0.15− 2.38% (w/w), the measured dissolution rate varied between 0.05 and 0.24 μmoles m−2 s−1 at 200 °C. Separate tests showed that thiols and, to a lesser extent, organic sulfides increased the solubility of α-HgS(s) in isooctane at room temperature compared to thiophenes, disulfides, and elemental sulfur. Long-term (14 days) α-HgS(s) solubility tests in a crude oil at 200 °C generated dissolved Hg concentrations in the 0.3% (w/w) range. The high α-HgS(s) dissolving capacity of the crude oils was more than 2 orders of magnitude greater than the highest reported Hg concentration in crude oils globally. On the basis of the kinetic and solubility data, it was further concluded that α-HgS(s) is not stable under typical petroleum reservoir conditions and would decompose to elemental mercury (Hg0 ). Our results suggest that source/reservoir temperature, abundance of reduced sulfur compounds in the crude oil, and dissolved Hg0 evasion processes are principal factors controlling the ultimate Hg concentration in a specific crude oil deposit.

  • 50.
    Larsson, Tom
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Frech, Wolfgang
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Species specific isotope dilution with on line derivatisation for determination of gaseous mercury species2005In: Journal of Analytical Atomic Spectrometry, ISSN 0267-9477, E-ISSN 1364-5544, Vol. 20, no 11, p. 1232-1239Article in journal (Refereed)
    Abstract [en]

    A species specific isotope dilution (SSID) method for determination of the volatile mercury (Hg) species Hg0, (CH3)2Hg, CH3HgX and HgX2(where X is a counter ion) in gaseous samples was developed. The procedure involved on line derivatisation of ionic Hg species with sodium tetraethylborate during sampling, before collection of species on a Tenax TA tube in series with an Au–Pt tube. Collected species were thermally desorbed and determined by GC-ICP-MS. The procedure provided absolute detection limits of 0.5 pg for CH3HgX and (CH3)2Hg, 5 pg for HgX2 and 25 pg for Hg0. Recoveries and transformations of the investigated species were studied for the different procedural steps and the method was tested for microcosm experiments on brackish water sediment samples, as well as for laboratory air samples. As a result of methylation and reduction processes within the sediment, gaseous emission rates could be determined for all investigated species after addition of an isotope enriched aqueous inorganic 199Hg2+ standard to the sediment. Hg0 was the only specie detected in laboratory air samples (4.5 ng m–3). The procedure for derivatisation of ionic Hg species prior to collection on Tenax TA reduces memory effects and transformations of CH3HgX and HgX2, which is especially advantageous at low sample gas flow rates and for complex gaseous matrices, such as emissions from sediment samples. SSID provides simplified methodological development, as well as efficient correction for matrix induced losses and transformations of Hg species. The method could be useful for various biogeochemical studies of Hg, as well as for reliable risk assessments during, for example, waste management and soil remediation.

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