1
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Gutensohn M, Schaefer JK, Yunda E, Skyllberg U, Björn E. The Combined Effect of Hg(II) Speciation, Thiol Metabolism, and Cell Physiology on Methylmercury Formation by Geobacter sulfurreducens. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:7185-7195. [PMID: 37098211 PMCID: PMC10173453 DOI: 10.1021/acs.est.3c00226] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The chemical and biological factors controlling microbial formation of methylmercury (MeHg) are widely studied separately, but the combined effects of these factors are largely unknown. We examined how the chemical speciation of divalent, inorganic mercury (Hg(II)), as controlled by low-molecular-mass thiols, and cell physiology govern MeHg formation by Geobacter sulfurreducens. We compared MeHg formation with and without addition of exogenous cysteine (Cys) to experimental assays with varying nutrient and bacterial metabolite concentrations. Cysteine additions initially (0-2 h) enhanced MeHg formation by two mechanisms: (i) altering the Hg(II) partitioning from the cellular to the dissolved phase and/or (ii) shifting the chemical speciation of dissolved Hg(II) in favor of the Hg(Cys)2 complex. Nutrient additions increased MeHg formation by enhancing cell metabolism. These two effects were, however, not additive since cysteine was largely metabolized to penicillamine (PEN) over time at a rate that increased with nutrient addition. These processes shifted the speciation of dissolved Hg(II) from complexes with relatively high availability, Hg(Cys)2, to complexes with lower availability, Hg(PEN)2, for methylation. This thiol conversion by the cells thereby contributed to stalled MeHg formation after 2-6 h Hg(II) exposure. Overall, our results showed a complex influence of thiol metabolism on microbial MeHg formation and suggest that the conversion of cysteine to penicillamine may partly suppress MeHg formation in cysteine-rich environments like natural biofilms.
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Affiliation(s)
| | - Jeffra K Schaefer
- Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, New Jersey 08901, United States
| | - Elena Yunda
- Department of Chemistry, Umeå University, SE- 90187 Umeå, Sweden
| | - Ulf Skyllberg
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden
| | - Erik Björn
- Department of Chemistry, Umeå University, SE- 90187 Umeå, Sweden
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2
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Capo E, Feng C, Bravo AG, Bertilsson S, Soerensen AL, Pinhassi J, Buck M, Karlsson C, Hawkes J, Björn E. Expression Levels of hgcAB Genes and Mercury Availability Jointly Explain Methylmercury Formation in Stratified Brackish Waters. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:13119-13130. [PMID: 36069707 PMCID: PMC9494745 DOI: 10.1021/acs.est.2c03784] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Neurotoxic methylmercury (MeHg) is formed by microbial methylation of inorganic divalent Hg (HgII) and constitutes severe environmental and human health risks. The methylation is enabled by hgcA and hgcB genes, but it is not known if the associated molecular-level processes are rate-limiting or enable accurate prediction of MeHg formation in nature. In this study, we investigated the relationships between hgc genes and MeHg across redox-stratified water columns in the brackish Baltic Sea. We showed, for the first time, that hgc transcript abundance and the concentration of dissolved HgII-sulfide species were strong predictors of both the HgII methylation rate and MeHg concentration, implying their roles as principal joint drivers of MeHg formation in these systems. Additionally, we characterized the metabolic capacities of hgc+ microorganisms by reconstructing their genomes from metagenomes (i.e., hgc+ MAGs), which highlighted the versatility of putative HgII methylators in the water column of the Baltic Sea. In establishing relationships between hgc transcripts and the HgII methylation rate, we advance the fundamental understanding of mechanistic principles governing MeHg formation in nature and enable refined predictions of MeHg levels in coastal seas in response to the accelerating spread of oxygen-deficient zones.
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Affiliation(s)
- Eric Capo
- Department
of Chemistry, Umeå University, Umeå 901 87, Sweden
- Department
of Aquatic Sciences and Assessment, Swedish
University of Agricultural Sciences, Uppsala 750 07, Sweden
| | - Caiyan Feng
- Department
of Chemistry, Umeå University, Umeå 901 87, Sweden
| | - Andrea G. Bravo
- Department
of Marine Biology and Oceanography, Institute of Marine Sciences, Spanish National Research Council (CSIC), Barcelona 08003, Spain
| | - Stefan Bertilsson
- Department
of Aquatic Sciences and Assessment, Swedish
University of Agricultural Sciences, Uppsala 750 07, Sweden
| | - Anne L. Soerensen
- Department
of Environmental Research and Monitoring, Swedish Museum of Natural History, Stockholm 104 05, Sweden
| | - Jarone Pinhassi
- Centre
for Ecology and Evolution in Microbial Model Systems—EEMiS, Linnaeus University, Kalmar 391 82, Sweden
| | - Moritz Buck
- Department
of Aquatic Sciences and Assessment, Swedish
University of Agricultural Sciences, Uppsala 750 07, Sweden
| | - Camilla Karlsson
- Centre
for Ecology and Evolution in Microbial Model Systems—EEMiS, Linnaeus University, Kalmar 391 82, Sweden
| | - Jeffrey Hawkes
- Department
of Chemistry, Uppsala University, Uppsala 751 23, Sweden
| | - Erik Björn
- Department
of Chemistry, Umeå University, Umeå 901 87, Sweden
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3
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Rodríguez J, Andersson A, Björn E, Timonen S, Brugel S, Skrobonja A, Rowe O. Inputs of Terrestrial Dissolved Organic Matter Enhance Bacterial Production and Methylmercury Formation in Oxic Coastal Water. Front Microbiol 2022; 13:809166. [PMID: 35966696 PMCID: PMC9363918 DOI: 10.3389/fmicb.2022.809166] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Accepted: 06/22/2022] [Indexed: 11/16/2022] Open
Abstract
Methylmercury (MeHg) is a potent neurotoxin commonly found in aquatic environments and primarily formed by microbial methylation of inorganic divalent mercury (Hg(II)) under anoxic conditions. Recent evidence, however, points to the production of MeHg also in oxic pelagic waters, but the magnitude and the drivers for this process remain unclear. Here, we performed a controlled experiment testing the hypothesis that inputs of terrestrial dissolved organic matter (tDOM) to coastal waters enhance MeHg formation via increased bacterial activity. Natural brackish seawater from a coastal area of the Baltic Sea was exposed to environmentally relevant levels of Hg(II) and additions of tDOM according to climate change scenarios. MeHg formation was observed to be coupled to elevated bacterial production rates, which, in turn, was linked to input levels of tDOM. The increased MeHg formation was, however, not coupled to any specific change in bacterial taxonomic composition nor to an increased abundance of known Hg(II) methylation genes. Instead, we found that the abundance of genes for the overall bacterial carbon metabolism was higher under increased tDOM additions. The findings of this study may have important ecological implications in a changing global climate by pointing to the risk of increased exposure of MeHg to pelagic biota.
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Affiliation(s)
- Juanjo Rodríguez
- Department of Ecology and Environmental Sciences, Umeå University, Umeå, Sweden
- Department of Microbiology, University of Helsinki, Helsinki, Finland
- *Correspondence: Juanjo Rodríguez,
| | - Agneta Andersson
- Department of Ecology and Environmental Sciences, Umeå University, Umeå, Sweden
- Umeå Marine Research Centre (UMF), Umeå University, Hörnefors, Sweden
| | - Erik Björn
- Department of Chemistry, Umeå University, Umeå, Sweden
| | - Sari Timonen
- Department of Microbiology, University of Helsinki, Helsinki, Finland
| | - Sonia Brugel
- Department of Ecology and Environmental Sciences, Umeå University, Umeå, Sweden
- Umeå Marine Research Centre (UMF), Umeå University, Hörnefors, Sweden
| | | | - Owen Rowe
- Helsinki Commission (HELCOM), Baltic Marine Environment Protection Commission, Helsinki, Finland
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4
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Liem-Nguyen V, Skyllberg U, Björn E. Methylmercury formation in boreal wetlands in relation to chemical speciation of mercury(II) and concentration of low molecular mass thiols. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 755:142666. [PMID: 33059147 DOI: 10.1016/j.scitotenv.2020.142666] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 09/22/2020] [Accepted: 09/22/2020] [Indexed: 06/11/2023]
Abstract
Methylmercury (MeHg) is a neurotoxin formed from inorganic divalent mercury (HgII) via microbial methylation, and boreal wetlands have been identified as major sources of MeHg. There is however a lack of studies investigating the relationship between the chemical speciation of HgII and MeHg formation in such environments, in particular regarding to role of thiol compounds. We determined HgII methylation potentials, kmeth, in boreal wetland soils using two HgII isotope tracers: 198Hg(OH)2(aq) and HgII bonded to thiol groups in natural organic matter, 200HgII-NOM(ads), representing HgII sources with high and low availability for methylation. The 198Hg(OH)2(aq) tracer was consistently methylated to a 5-fold higher extent than 200HgII-NOM(ads), independent of environmental conditions. This suggests that the concentration of HgII in porewater was a decisive factor for HgII methylation. A comprehensive thermodynamic speciation model (including HgII complexes with inorganic sulfide (H2S), polysulfides (H2Sn), thiols associated with natural organic matter (NOM-RSH) and specific low molecular mass thiols (LMM-RSH) provided new insights on the speciation of HgII in boreal wetland porewaters, but did not demonstrate any clear relationship between kmeth and the calculated chemical speciation. In contrast, significant positive relationships were observed between kmeth and the sum of LMM thiol compounds of biological origin. We suggest two possible mechanisms underlying these correlations: 1) LMM thiols kinetically control the size and composition of the HgII pool available for microbial uptake, and/or 2) LMM thiols are produced by microbes such that the correlation reflects a relation between microbial activity and MeHg formation.
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Affiliation(s)
- Van Liem-Nguyen
- Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden; Laboratory of Advanced Materials Chemistry, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City, Viet Nam
| | - Ulf Skyllberg
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden
| | - Erik Björn
- Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden.
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5
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Åkerblom S, Nilsson MB, Skyllberg U, Björn E, Jonsson S, Ranneby B, Bishop K. Formation and mobilization of methylmercury across natural and experimental sulfur deposition gradients. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2020; 263:114398. [PMID: 32229372 DOI: 10.1016/j.envpol.2020.114398] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 03/11/2020] [Accepted: 03/16/2020] [Indexed: 06/10/2023]
Abstract
We investigated the influence of sulfate (SO42-) deposition and concentrations on the net formation and solubility of methylmercury (MeHg) in peat soils. We used data from a natural sulfate deposition gradient running 300 km across southern Sweden to test the hypothesis posed by results from an experimental field study in northern Sweden: that increased loading of SO42- both increases net MeHg formation and redistributes methylmercury (MeHg) from the peat soil to its porewater. Sulfur concentrations in peat soils correlated positively with MeHg concentrations in peat porewater, along the deposition gradient similar to the response to added SO42- in the experimental field study. The combined results from the experimental field study and deposition gradient accentuate the multiple, distinct and interacting roles of SO42- deposition in the formation and redistribution of MeHg in the environment.
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Affiliation(s)
- Staffan Åkerblom
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Lennart Hjelms väg 9, SE-756 51, Uppsala, Sweden.
| | - Mats B Nilsson
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden
| | - Ulf Skyllberg
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden
| | - Erik Björn
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden
| | - Sofi Jonsson
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden; Department of Environmental Science and Analytical Chemistry, SE-11418 Stockholm University Stockholm, Sweden
| | - Bo Ranneby
- Department of Forest Economics, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden
| | - Kevin Bishop
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Lennart Hjelms väg 9, SE-756 51, Uppsala, Sweden
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6
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Skrobonja A, Gojkovic Z, Soerensen AL, Westlund PO, Funk C, Björn E. Uptake Kinetics of Methylmercury in a Freshwater Alga Exposed to Methylmercury Complexes with Environmentally Relevant Thiols. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:13757-13766. [PMID: 31682417 DOI: 10.1021/acs.est.9b05164] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Cellular uptake of dissolved methylmercury (MeHg) by phytoplankton is the most important point of entry for MeHg into aquatic food webs. However, the process is not fully understood. In this study we investigated the influence of chemical speciation on rate constants for MeHg accumulation by the freshwater green microalga Selenastrum capricornutum. We used six MeHg-thiol complexes with moderate but important structural differences commonly found in the environment. Rate constants for MeHg interactions with cells were determined for the MeHg-thiol treatments and a control assay containing the thermodynamically less stable MeHgOH complex. We found both elevated amounts of MeHg associated with whole cells and higher MeHg association rate constants in the control compared to the thiol treatments. Furthermore, the association rate constants were lower when algae were exposed to MeHg complexes with thiols of larger size and more "branched" chemical structure compared to complexes with simpler structure. The results further demonstrated that the thermodynamic stability and chemical structure of MeHg complexes in the medium is an important controlling factor for the rate of MeHg interactions with the cell surface, but not for the MeHg exchange rate across the membrane. Our results are in line with uptake mechanisms involving formation of MeHg complexes with cell surface ligands prior to internalization.
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Affiliation(s)
| | - Zivan Gojkovic
- Umeå University , Department of Chemistry , SE-901 87 Umeå , Sweden
| | - Anne L Soerensen
- Stockholm University , Department of Environmental Science and Analytical Chemistry , SE-106 97 Stockholm , Sweden
| | | | - Christiane Funk
- Umeå University , Department of Chemistry , SE-901 87 Umeå , Sweden
| | - Erik Björn
- Umeå University , Department of Chemistry , SE-901 87 Umeå , Sweden
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7
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Adediran GA, Liem-Nguyen V, Song Y, Schaefer JK, Skyllberg U, Björn E. Microbial Biosynthesis of Thiol Compounds: Implications for Speciation, Cellular Uptake, and Methylation of Hg(II). ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:8187-8196. [PMID: 31257868 DOI: 10.1021/acs.est.9b01502] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
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)2 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)2 complexes. The Hg(II) methylation rate across different Hg(LMM-RS)2 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.
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Affiliation(s)
| | - Van Liem-Nguyen
- Department of Chemistry , Umeå University , SE- 90187 Umeå , Sweden
- School of Science and Technology , Örebro University , SE-70182 Örebro , Sweden
| | - Yu Song
- Department of Forest Ecology and Management , Swedish University of Agricultural Sciences , SE-901 83 Umeå , Sweden
| | - Jeffra K Schaefer
- Department of Environmental Sciences , Rutgers University , 14 College Farm Road , New Brunswick , New Jersey 08901 , United States
| | - Ulf Skyllberg
- Department of Forest Ecology and Management , Swedish University of Agricultural Sciences , SE-901 83 Umeå , Sweden
| | - Erik Björn
- Department of Chemistry , Umeå University , SE- 90187 Umeå , Sweden
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8
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Soerensen AL, Schartup AT, Skrobonja A, Björn E. Organic matter drives high interannual variability in methylmercury concentrations in a subarctic coastal sea. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2017. [PMID: 28646796 DOI: 10.1016/j.envpol.2017.06.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Levels of neurotoxic methylmercury (MeHg) in phytoplankton are strongly associated with water MeHg concentrations. Because uptake by phytoplankton is the first and largest step of bioaccumulation in aquatic food webs many studies have investigated factors driving seasonal changes in water MeHg concentrations. Organic matter (OM) is widely accepted as an important driver of MeHg production and uptake by phytoplankton but is also known for strong interannual variability in concentration and composition within systems. In this study, we explore the role of OM on spatial and interannual variability of MeHg in a subarctic coastal sea, the northern Baltic Sea. Using MeHg (2014: 80 ± 25 fM; 2015: <LOD; 2016: 21 ± 9 fM) and OM measurements during late summer/early fall, we find that dissolved organic carbon (DOC) and humic matter content explain 60% of MeHg variability. We find that while labile DOC increases MeHg levels in the water, humic content reduces it. We propose that the positive association between MeHg and labile DOC shows that labile DOC is a proxy for OM remineralization rate in nearshore and offshore waters. This is consistent with other studies finding that in situ MeHg production in the water column occurs during OM remineralization. The negative association between water humic content and MeHg concentration is most likely due to humic matter decreasing inorganic mercury (HgII) bioavailability to methylating microbes. With these relationships, we develop a statistical model and use it to calculate MeHg concentrations in late summer nearshore and offshore waters between 2006 and 2016 using measured values for water DOC and humic matter content. We find that MeHg concentrations can vary by up to an order of magnitude between years, highlighting the importance of considering interannual variability in water column MeHg concentrations when interpreting both short and long term MeHg trends in biota.
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Affiliation(s)
- A L Soerensen
- Stockholm University, Department of Environmental Science and Analytical Chemistry, Stockholm, Sweden.
| | - A T Schartup
- Harvard University, John A. Paulson School of Engineering and Applied Sciences, Cambridge MA, USA
| | - A Skrobonja
- Umeå University, Department of Chemistry, Umeå, Sweden
| | - E Björn
- Umeå University, Department of Chemistry, Umeå, Sweden
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9
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Affiliation(s)
- Eva M. Krupp
- University of Aberdeen; Chemistry Department; Meston Walk Aberdeen AB24 3UE UK
| | - Zuzana Gajdosechova
- University of Aberdeen; Chemistry Department; Meston Walk Aberdeen AB24 3UE UK
| | - Tanja Schwerdtle
- University of Potsdam, Institute of Nutritional Science; Department of Food Chemistry; Arthur-Scheunert-Allee 114-116 14558 Nuthetal Germany
| | - Hanna Lohren
- University of Potsdam, Institute of Nutritional Science; Department of Food Chemistry; Arthur-Scheunert-Allee 114-116 14558 Nuthetal Germany
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10
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Levanoni O, Bishop K, Mckie BG, Hartman G, Eklöf K, Ecke F. Impact of Beaver Pond Colonization History on Methylmercury Concentrations in Surface Water. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2015; 49:12679-12687. [PMID: 26450629 DOI: 10.1021/acs.est.5b03146] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Elevated concentrations of methylmercury (MeHg) in freshwater ecosystems are of major environmental concern in large parts of the northern hemisphere. Beaver ponds have been identified as a potentially important source of MeHg. The role of beavers might be especially pronounced in large parts of Europe, where beaver populations have expanded rapidly following near-extirpation. This study evaluates the role of the age and colonization history (encompassing patterns of use and reuse) of ponds constructed by the Eurasian beaver Castor fiber in regulating MeHg concentrations in Swedish streams. In 12 beaver systems located in three regions, we quantified MeHg concentrations together with other relevant parameters on five occasions per year in 2012-2013. Five were pioneer systems, inundated for the first time since beaver extirpation, and seven were recolonized, with dams reconstructed by newly recolonizing beavers. MeHg concentrations in pioneer but not in recolonized beaver systems were up to 3.5 fold higher downstream than upstream of the ponds, and varied between seasons and years. Our results show that pioneer inundation by beavers can increase MeHg concentrations in streams, but that this effect is negligible when dams are reconstructed on previously used ponds. We therefore expect that the recovery and expansion of beavers in the boreal system will only have a transitional effect on MeHg in the environment.
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Affiliation(s)
- Oded Levanoni
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden
| | - Kevin Bishop
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden
- Department of Earth Sciences, Air Water and Landscape Sciences, Villavägen 16, Uppsala University , SE-752 36 Uppsala, Sweden
| | - Brendan G Mckie
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden
| | - Göran Hartman
- Department of Ecology, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden
| | - Karin Eklöf
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden
| | - Frauke Ecke
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden
- Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, (SLU) , SE-901 83 Umeå, Sweden
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11
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Eklöf K, Schelker J, Sørensen R, Meili M, Laudon H, von Brömssen C, Bishop K. Impact of forestry on total and methyl-mercury in surface waters: distinguishing effects of logging and site preparation. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:4690-8. [PMID: 24666406 DOI: 10.1021/es404879p] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Forestry operations can increase the export of mercury (both total and methyl) to surface waters. However, little is known about the relative contribution of different forestry practices. We address this question using a paired-catchment study that distinguishes the effects of site preparation from the antecedent logging. Runoff water from three catchments, two harvested and one untreated control, was sampled biweekly during one year prior to logging, two years after logging, and three years after site preparation. The logging alone did not significantly increase the concentrations of either total or methyl-mercury in runoff, but export increased by 50-70% in one of the harvested catchments as a consequence of increased runoff volume. The combined effects of logging and site preparation increased total and methyl-mercury concentrations by 30-50% relative to preharvest conditions in both treated catchments. The more pronounced concentration effect after site preparation compared to logging could be related to site preparation being conducted during summer. This caused more soil disturbance than logging, which was done during winter with snow covering the ground. The results suggest that the cumulative impact of forest harvest on catchment mercury outputs depends on when and how forestry operations are implemented.
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Affiliation(s)
- Karin Eklöf
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences , Box 7050, SE-75007, Uppsala, Sweden
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12
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Trümpler S, Meermann B, Nowak S, Buscher W, Karst U, Sperling M. In vitro study of thimerosal reactions in human whole blood and plasma surrogate samples. J Trace Elem Med Biol 2014; 28:125-130. [PMID: 24613139 DOI: 10.1016/j.jtemb.2014.01.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/24/2013] [Revised: 01/28/2014] [Accepted: 01/29/2014] [Indexed: 01/28/2023]
Abstract
Because of its bactericidal and fungicidal properties, thimerosal is used as a preservative in drugs and vaccines and is thus deliberately injected into the human body. In aqueous environment, it decomposes into thiosalicylic acid and the ethylmercury cation. This organomercury fragment is a potent neurotoxin and is suspected to have similar toxicity and bioavailability like the methylmercury cation. In this work, human whole blood and physiological simulation solutions were incubated with thimerosal to investigate its behaviour and binding partners in the blood stream. Inductively coupled plasma with optical emission spectrometry (ICP-OES) was used for total mercury determination in different blood fractions, while liquid chromatography (LC) coupled to electrospray ionisation time-of-flight (ESI-TOF) and inductively coupled plasma-mass spectrometry (ICP-MS) provided information on the individual mercury species in plasma surrogate samples. Analogous behaviour of methylmercury and ethylmercury species in human blood was shown and an ethylmercury-glutathione adduct was identified.
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Affiliation(s)
- Stefan Trümpler
- University of Münster, Institute of Inorganic and Analytical Chemistry, Corrensstr. 30, Münster 48149, Germany
| | - Björn Meermann
- University of Münster, Institute of Inorganic and Analytical Chemistry, Corrensstr. 30, Münster 48149, Germany; Federal Institute of Hydrology, Department G2 - Aquatic Chemistry, Am Mainzer Tor 1, 56068 Koblenz, Germany
| | - Sascha Nowak
- University of Münster, Institute of Inorganic and Analytical Chemistry, Corrensstr. 30, Münster 48149, Germany
| | - Wolfgang Buscher
- University of Münster, Institute of Inorganic and Analytical Chemistry, Corrensstr. 30, Münster 48149, Germany
| | - Uwe Karst
- University of Münster, Institute of Inorganic and Analytical Chemistry, Corrensstr. 30, Münster 48149, Germany
| | - Michael Sperling
- University of Münster, Institute of Inorganic and Analytical Chemistry, Corrensstr. 30, Münster 48149, Germany; European Virtual Institute for Speciation Analysis, Mendelstr. 11, Münster 48149, Germany.
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13
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Pietilä H, Perämäki P, Piispanen J, Majuri L, Starr M, Nieminen T, Kantola M, Ukonmaanaho L. Determination of methyl mercury in humic-rich natural water samples using N2-distillation with isotope dilution and on-line purge and trap GC-ICP-MS. Microchem J 2014. [DOI: 10.1016/j.microc.2013.10.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Fernández-Gómez C, Drott A, Björn E, Díez S, Bayona JM, Tesfalidet S, Lindfors A, Skyllberg U. Towards universal wavelength-specific photodegradation rate constants for methyl mercury in humic waters, exemplified by a Boreal lake-wetland gradient. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:6279-87. [PMID: 23647363 DOI: 10.1021/es400373s] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
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.
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Yin Y, Liu J, Jiang G. Recent advances in speciation analysis of mercury, arsenic and selenium. ACTA ACUST UNITED AC 2012. [DOI: 10.1007/s11434-012-5497-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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16
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Bergman I, Bishop K, Tu Q, Frech W, Åkerblom S, Nilsson M. The influence of sulphate deposition on the seasonal variation of peat pore water methyl Hg in a boreal mire. PLoS One 2012; 7:e45547. [PMID: 23029086 PMCID: PMC3448652 DOI: 10.1371/journal.pone.0045547] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2012] [Accepted: 08/23/2012] [Indexed: 11/19/2022] Open
Abstract
In this paper we investigate the hypothesis that long-term sulphate (SO42−) deposition has made peatlands a larger source of methyl mercury (MeHg) to remote boreal lakes. This was done on experimental plots at a boreal, low sedge mire where the effect of long-term addition of SO42− on peat pore water MeHg concentrations was observed weekly throughout the snow-free portion of 1999. The additions of SO42− started in 1995. The seasonal mean of the pore water MeHg concentrations on the plots with 17 kg ha−1 yr−1 of sulphur (S) addition (1.3±0.08 ng L−1, SE; n = 44) was significantly (p<0.0001) higher than the mean MeHg concentration on the plots with 3 kg ha−1 yr−1 of ambient S deposition (0.6±0.02 ng L−1, SE; n = 44). The temporal variation in pore water MeHg concentrations during the snow free season was larger in the S-addition plots, with an amplitude of >2 ng L−1 compared to +/−0.5 ng L−1 in the ambient S deposition plots. The concentrations of pore water MeHg in the S-addition plots were positively correlated (r2 = 0.21; p = 0.001) to the groundwater level, with the lowest concentrations of MeHg during the period with the lowest groundwater levels. The pore water MeHg concentrations were not correlated to total Hg, DOC concentration or pH. The results from this study indicate that the persistently higher pore water concentrations of MeHg in the S-addition plots are caused by the long-term additions of SO42− to the mire surface. Since these waters are an important source of runoff, the results support the hypothesis that SO42− deposition has increased the contribution of peatlands to MeHg in downstream aquatic systems. This would mean that the increased deposition of SO42− in acid rain has contributed to the modern increase in the MeHg burdens of remote lakes hydrologically connected to peatlands.
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Affiliation(s)
- Inger Bergman
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden
| | - Kevin Bishop
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden
- Department of Earth Sciences, Uppsala University, Uppsala, Sweden
| | - Qiang Tu
- Department of Analytical Chemistry, University of Umeå, Umeå, Sweden
| | - Wolfgang Frech
- Department of Analytical Chemistry, University of Umeå, Umeå, Sweden
| | - Staffan Åkerblom
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Mats Nilsson
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden
- * E-mail:
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Eklöf K, Kraus A, Weyhenmeyer GA, Meili M, Bishop K. Forestry Influence by Stump Harvest and Site Preparation on Methylmercury, Total Mercury and Other Stream Water Chemistry Parameters Across a Boreal Landscape. Ecosystems 2012. [DOI: 10.1007/s10021-012-9586-3] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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18
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Tjerngren I, Meili M, Björn E, Skyllberg U. Eight boreal wetlands as sources and sinks for methyl mercury in relation to soil acidity, C/N ratio, and small-scale flooding. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2012; 46:8052-60. [PMID: 22800474 DOI: 10.1021/es300845x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Four years of catchment export and wetland input-output mass balances are reported for inorganic Hg (Hg(inorg)), methyl mercury (MeHg), dissolved organic carbon (DOC), and sulfate in eight Swedish boreal wetlands. All wetlands had a history of artificial drainage and seven were subjected to small-scale flooding during the complete study period (two sites) or the two last years (five sites). We used an approach in which specific runoff data determined at hydrological stations situated at a distance from the studied sites were used in the calculation of water and element budgets. All wetlands except one were significant sinks for Hg(inorg). Seven wetlands were consistent sources of MeHg and one (an Alnus glutinosa swamp) was a significant sink. The pattern of MeHg yields was in good agreement with previously determined methylation and demethylation rates in the wetland soils of this study, with a maximum MeHg yield obtained in wetlands with an intermediate soil acidity (pH ∼5.0) and C/N ratio (∼20). We hypothesize that an increased nutrient status from poor to intermediate conditions promotes methylation over demethylation, whereas a further increase in nutrient status and trophy to meso- and eutrophic conditions promotes demethylation over methylation. Small-scale flooding showed no or moderate changes in MeHg yield, maintaining differences among wetlands related to nutrient status.
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Affiliation(s)
- Ida Tjerngren
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences , SE-901 83 Umeå, Sweden
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Taylor VF, Carter A, Davies C, Jackson BP. Trace-Level Automated Mercury Speciation Analysis. ANALYTICAL METHODS : ADVANCING METHODS AND APPLICATIONS 2011; 3:1143-1148. [PMID: 21572543 PMCID: PMC3092719 DOI: 10.1039/c0ay00528b] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
An automated system for methyl Hg analysis by purge and trap gas chromatography (GC) was evaluated, with comparison of several different instrument configurations including chromatography columns (packed column or capillary), detector (atomic fluorescence, AFS, or inductively coupled plasma mass spectrometry, ICP-MS, using quadrupole and sector field ICP- MS instruments). Method detection limits (MDL) of 0.042 pg and 0.030 pg for CH(3)Hg(+) were achieved with the automated Hg analysis system configured with AFS and ICPMS detection, respectively. Capillary GC with temperature programming was effective in improving resolution and decreasing retention times of heavier Hg species (in this case C(3)H(7)Hg(+)) although carryover between samples was increased. With capillary GC, the MDL for CH(3)Hg(+) was 0.25 pg for AFS detection and 0.060 pg for ICP-MS detection. The automated system was demonstrated to have high throughput (72 samples analyzed in 8 hours) requiring considerably less analyst time than the manual method for methyl mercury analysis described in EPA 1630.
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Affiliation(s)
- Vivien F Taylor
- Trace Element Analysis Core, Dartmouth College, 6105 Fairchild, Hanover NH 03755
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20
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Popp M, Hann S, Koellensperger G. Environmental application of elemental speciation analysis based on liquid or gas chromatography hyphenated to inductively coupled plasma mass spectrometry—A review. Anal Chim Acta 2010; 668:114-29. [DOI: 10.1016/j.aca.2010.04.036] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2010] [Revised: 04/16/2010] [Accepted: 04/19/2010] [Indexed: 10/19/2022]
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21
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Skyllberg U, Westin MB, Meili M, Björn E. Elevated concentrations of methyl mercury in streams after forest clear-cut: a consequence of mobilization from soil or new methylation? ENVIRONMENTAL SCIENCE & TECHNOLOGY 2009; 43:8535-41. [PMID: 20028048 DOI: 10.1021/es900996z] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Concentrations of inorganic, mercuric mercury (Hg(II)), methyl mercury (MeHg) and ancillary chemistry measured in first-order streams draining 0-4 (N = 20) and 4-10 (N = 27) year-old clear-cuts of former Norway Spruce Picea abies (Karst.) forest stands were compared with concentrations in streams draining >70 year-old Norway Spruce reference stands (N = 10). Concentrations of MeHg, and ratios of MeHg TOC(-1) and Hg(II) TOC(-1), were significantly (p < 0.01) elevated in 0-4 year-old clear-cuts, as compared to references. The only ancillary variable showing a significant elevation for 0-4 year-old clear-cuts was Mn (p < 0.02). The 4-10 year-old clear-cuts showed intermediate concentrations with nonsignificant differences as compared to references. pH, nitrate, sulfate, Ca, Fe, TOC, TON, and the aromaticity of TOC (SUVA(254 nm)) showed nonsignificant differences between clear-cut age classes and references. Assuming that MeHg and Hg(II) are mobilized from soil to stream to a similar relative extent as a consequence of clear-cutting, a calculation showed that (1)/(6) of the elevated MeHg concentration was due to enhanced mobilization from soil and (5)/(6) was due to new methylation of Hg(II) 0-4 years after clear-cut. New methylation after clear-cut is suggested to be stimulated by an increased availability of electron donors for methylating bacteria, as a consequence of degradation of logging residue ("slash") and soil organic matter. A subdivision of sites situated above and below the highest postglacial coastline (HC) revealed a significant elevation of MeHg, MeHg TOC(-1) and Hg(II) TOC(-1) (p < 0.05) beyond their references in 0-4 year-old clear-cuts above (but not below) the HC. This suggests that postglacial deposits of FeS(s) and FeS(2)(s) were not an important factor for elevation of MeHg after clear-cut.
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Affiliation(s)
- Ulf Skyllberg
- Department of Forest Ecology, Swedish University of Agricultural Sciences, SE-90183 Umeå, Sweden.
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Liu J, Li F, Lin S, Li Z, Chen Y, Lin H, Huang L, Cai J, Chen X. Solid Substrate Room Temperature Phosphorimetry for the Determination of Trace Mercury Based on the Reaction between Alkaline Phosphatase and Mercury Using Triton X-100 as a Sensitizer. CHINESE J CHEM 2009. [DOI: 10.1002/cjoc.200990301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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23
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Jackson B, Taylor V, Baker RA, Miller E. Low-level mercury speciation in freshwaters by isotope dilution GC-ICP-MS. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2009; 43:2463-9. [PMID: 19452902 PMCID: PMC2692077 DOI: 10.1021/es802656p] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Atmospheric deposition of anthropogenic Hg has led to increased Hg concentrations in many ecosystems. Modeling is an effective method for predicting the complex dynamics of Hg transport in watersheds. Such models require accurate concentrations of water column methylmercury, CH3Hg+, for input parameters, yet these concentrations are very difficult to measure precisely because they are so low. We developed a method for aqueous CH3Hg+ quantification in Lake Champlain, VT, where ambient CH3Hg+ concentrations are < 0.04 ng L(-1). The analysis utilized species-specific isotope dilution, purge and trap gas chromatography inductively coupled plasma mass spectrometry and provided instrument detection limits of about 0.3 fM (0.06 pg L(-1)) and method detection limits of 15 fM (0.003 ng L(-1)) for CH3Hg+, which are among the lowest reported. Artifactual methylation of inorganic Hg(2+) was shown to be minor, and the precision of the isotope dilution method was generally <5% relative standard deviation, which is much lower than would have been the case for an external calibration approach. The method is accurate even at low concentrations of 0.025 ng L(-1). This combination of precision, accuracy, and low detection allows for quantification of significant differences in CH3Hg+ concentration between bays and over time within bays of Lake Champlain, where mean CH3Hg+ concentrations differ by only 0.006 ng L(-1) at concentrations as low as 0.014 ng L(-1).
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Affiliation(s)
- Brian Jackson
- Trace Element Analysis Core, Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA.
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Drott A, Lambertsson L, Björn E, Skyllberg U. Do potential methylation rates reflect accumulated methyl mercury in contaminated sediments? ENVIRONMENTAL SCIENCE & TECHNOLOGY 2008; 42:153-8. [PMID: 18350890 DOI: 10.1021/es0715851] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
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 degrees 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.
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Affiliation(s)
- Andreas Drott
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, S-90183 Umeå, Sweden.
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Björn E, Larsson T, Lambertsson L, Skyllberg U, Frech W. Recent advances in mercury speciation analysis with focus on spectrometric methods and enriched stable isotope applications. AMBIO 2007; 36:443-451. [PMID: 17985698 DOI: 10.1579/0044-7447(2007)36[443:raimsa]2.0.co;2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
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.
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Affiliation(s)
- Erik Björn
- Department of Chemistry, Umeå University, Sweden.
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Drott A, Lambertsson L, Björn E, Skyllberg U. Importance of dissolved neutral mercury sulfides for methyl mercury production in contaminated sediments. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2007; 41:2270-6. [PMID: 17438774 DOI: 10.1021/es061724z] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
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 degrees 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 subsets 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 (microg 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 (microg 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).
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Affiliation(s)
- Andreas Drott
- Department of Forest Ecology, Swedish University of Agricultural Sciences, S-90183 Umeå, Sweden
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Affiliation(s)
- Carolyn J Koester
- Forensic Science Center, Technical Information Department, Lawrence Livermore National Laboratory, Livermore, California 94551-0808, USA
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Métivier R, Leray I, Lebeau B, Valeur B. A mesoporous silica functionalized by a covalently bound calixarene-based fluoroionophore for selective optical sensing of mercury(ii) in water. ACTA ACUST UNITED AC 2005. [DOI: 10.1039/b501897h] [Citation(s) in RCA: 181] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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