| 1. |
- Regnell, Olof, et al.
(författare)
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Linking Cellulose Fiber Sediment Methyl Mercury Levels to Organic Matter Decay and Major Element Composition.
- 2014
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Ingår i: Ambio: a Journal of Human Environment. - : Springer Science and Business Media LLC. - 0044-7447. ; 43:7, s. 878-890
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Tidskriftsartikel (refereegranskat)abstract
- Methylation of mercury (Hg) to highly toxic methyl Hg (MeHg), a process known to occur when organic matter (OM) decomposition leads to anoxia, is considered a worldwide threat to aquatic ecosystems and human health. We measured temporal and spatial variations in sediment MeHg, total Hg (THg), and major elements in a freshwater lagoon in Sweden polluted with Hg-laden cellulose fibers. Fiber decomposition, confined to a narrow surface layer, resulted in loss of carbon (C), uptake of nitrogen (N), phosphorus (P), and sulfur (S), and increased MeHg levels. Notably, fiber decomposition and subsequent erosion of fiber residues will cause buried contaminants to gradually come closer to the sediment-water interface. At an adjacent site where decomposed fiber accumulated, there was a gain in C and a loss of S when MeHg increased. As evidenced by correlation patterns and vertical chemical profiles, reduced S may have fueled C-fixation and Hg methylation at this site.
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| 2. |
- Regnell, Olof, et al.
(författare)
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Methyl mercury production in freshwater microcosms affected by dissolved oxygen levels : Role of cobalamin and microbial community composition
- 1996
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 53:7, s. 1535-1545
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Tidskriftsartikel (refereegranskat)abstract
- Radiolabelled Hg(NO(NO3)2 was added to microcosms containing water and sediment from a lake contaminated with cellulose fibres and mercury. We found that anoxic incubation resulted in methyl 203Hg concentrations in the water at least an order of magnitude higher than the levels in oxygenated incubation. This was explained by the fact that both the production and the water solubility of methyl mercury were higher under anoxic conditions than under oxic conditions. Demethylation, however, seemed to play a minor role, if any, in regulating methyl mercury concentrations. In the sediment, the level of methyl 203Hg was strongly correlated with the level of cobalamin and the levels of the phospholipid fatty acids i15:0 and 10Mel 6:0, the latter indicating the presence of Desulfobacter, a genus of sulphate-reducing bacteria.
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| 3. |
- Eckley, CS, et al.
(författare)
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Mercury methylation in the hypolimnetic waters of lakes with and without connection to wetlands in northern Wisconsin
- 2005
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 1205-7533. ; 62:2, s. 400-411
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Tidskriftsartikel (refereegranskat)abstract
- Rates of Hg methylation and demethylation were measured in anoxic hypolimnetic waters of two pristine Wisconsin lakes using stable isotopes of Hg as tracers. One of the lakes is a clear-water seepage lake situated in sandy terrain with minimal wetland influence. The other is a dark-water lake receiving channelized inputs from a relatively large terrestrial wetland. Methyl mercury (MeHg) accumulated in the anoxic hypolimnia of both lakes during summer stratification, reaching concentrations of 0.8 ng center dot L-1 in the clear-water lake and 5 ng center dot L-1 in the dark-water lake. The stable isotopic assays indicated that rate constants of Hg-(II) methylation (K-m) ranged from 0.01 to 0.04 center dot day(-1) in the clear-water lake and from 0.01 to 0.09 center dot day(-1) in the dark-water lake, depending on the depth stratum. On average, K-m was threefold greater in the dark-water lake. Hypolimnetic demethylation rate constants (K-dm) averaged 0.03 center dot day(-1) in the clear-water lake and 0.05 center dot day(-1) in the dark-water lake. These methylation rates were sufficient to account for the observed accumulation of MeHg in hypolimnetic water during summer in both lakes. Despite substantial export of MeHg from the wetland to the dark-water lake, our study indicates that in-lake production and decomposition of MeHg dominated the MeHg cycle in both lakes.
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| 4. |
- Ekström, Sara M., et al.
(författare)
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Increasing concentrations of iron in surface waters as a consequence of reducing conditions in the catchment area
- 2016
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 121:2, s. 479-493
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies report trends of strongly increasing iron (Fe) concentrations in freshwaters. Since Fe is a key element with a decisive role in the biogeochemical cycling of major elements, it is important to understand the mechanisms behind these trends. We hypothesized that variations in Fe concentration are driven mainly by redox dynamics in hydraulically connected soils. Notably, Fe(III), which is the favored oxidation state except in environments where microbial activity provide strong reducing intensity, has several orders of magnitude lower water solubility than Fe(II). To test our hypothesis, seasonal variation in water chemistry, discharge, and air temperature was studied in three Swedish rivers. Methylmercury and sulfate were used as indicators of seasonal redox changes. Seasonal variability in water chemistry, discharge, and air temperature in the Eman and Lyckeby Rivers implied that the variation in Fe was primarily driven by the prevalence of reducing conditions in the catchment. In general, high Fe concentrations were observed when methylmercury was high and sulfate was low, indicative of reducing conditions. The Fe concentrations showed no or weak relationships with variations in dissolved organic matter concentration and aromaticity. The seasonal variation in Fe concentration of the Ume river was primarily dependent on timing of the snowmelt in high- versus low-altitude areas of the catchment. There were long-term trends of increasing temperature in all catchments and also trends of increasing discharge in the southern rivers, which should increase the probability for anaerobic conditions in space and time and thereby increase Fe transport to the aquatic systems.
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| 5. |
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| 6. |
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| 7. |
- Regnell, Olof, et al.
(författare)
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Coupling of methyl and total mercury in a minerotrophic peat bog in southeastern Sweden
- 2004
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 1205-7533. ; 61:10, s. 2014-2023
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Tidskriftsartikel (refereegranskat)abstract
- During most of an annual cycle, we studied the temporal variation of total mercury (Hg-T) and methyl mercury (MeHg) in unfiltered and filtered (0.45 mu) peat water from a minerotrophic peat bog in southeastern Sweden. MeHg in bulk water ([MeHgT]) and total Hg in filtered water in discharge water from the peat bog ([Hg-D]) were an order of magnitude higher than in upland runoff water entering the peat bog. At the discharge end, peat-water [Hg-D] and [MeHgD] ranged from 8 to 54 pmol.L-1 and from 1 to 32 pmol.L-1, respectively. Whereas the variation of [MeHgT] was explained by changes in [MeHgD], the variation of inorganic Hg-T [IHgT] = [Hg-T] - [MeHgT] was explained by changes in particle-bound IHg [IHgP] = [IHgT] - [IHgD]. Filterable organic matter and sulfide in the water both correlated poorly with [Hg-D]. Neither did the amount of Hg-T in precipitation and upland runoff water correlate well with the estimated discharge of Hg-D from the peat bog. However, there was a strong correlation between [Hg-D] and [MeHgT] in the peat water (r = 0.96). Furthermore, a significant fraction of Hg-D was MeHg (mean 28%; range 8-60%). These results suggest that methylation increased the mobility of Hg.
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| 8. |
- Regnell, Olof, et al.
(författare)
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Effects of anoxia and sulfide on concentrations of total and methyl mercury in sediment and water in two Hg-polluted lakes
- 2001
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 1205-7533. ; 58:3, s. 506-517
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Tidskriftsartikel (refereegranskat)abstract
- Between May and December 1996, monthly samples of surface sediment (0-1 cm), settling matter, and water were taken at a shallow site and a deep site in each of two consecutive Hg-polluted riverine lakes. In the upper lake, the sediment was polluted also with cellulose fiber. Both hypolimnia turned anoxic, but sulfide was detected only in the upper lake. When sulfide appeared, hypolimnetic methyl mercury (MeHg) increased and reached 47 pM (9.4 ng.L-1), whereas MeHg in the sediment below decreased. The increase in hypolimnetic inorganic Hg (IHg = total Hg - MeHg), which reached a peak of 40 pM (8.0 ng.L-1), was slower, possibly because mobilized IHg was methylated. In the lower lake, hypolimnetic MeHg and IHg increased less dramatically during summer stratification, reaching only 5 and 24 pM (1.0 and 4.8 ng.L-1), respectively. There was no detectable concomitant decrease in sediment MeHg. In both lakes, MeHg appeared to increase simultaneously with total Fe and Mn in the hypolimnion, as did IHg in the lower lake. Our observations suggest that the presence of hydrous ferric and manganese oxides decreased the mobility of Hg in both lakes but increased MeHg production in the upper lake.
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| 9. |
- Regnell, Olof, et al.
(författare)
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Mercury in a Boreal Forest Stream - Role of Historical Mercury Pollution, TOC, Temperature, and Water Discharge
- 2009
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 1520-5851 .- 0013-936X. ; 43:10, s. 3514-3521
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Tidskriftsartikel (refereegranskat)abstract
- Over a one-year study period (2003), we monitored total Hg (HgT) and methyl Hg (MeHg) at two sites in a Swedish forest stream located above (Site(ref)) and below a stretch of Hg-contaminated sediments (Site(Hg)). We also monitored HgT, MeHg, and ancillary water chemistry in peat water close to the stream and HgT in open field wet deposition. Despite the presence of historical Hg contaminants, direct atmospheric Hg deposition and transfer of Hg from the catchment explained more than half of the annual HgT load at Site(Hg). The concentrations of both HgT and MeHg were sensitive to changes in water discharge (Q) and water temperature (T) at both sites, suggesting that the stream HgT and MeHg load can change dramatically in response to changing weather conditions. The 2003 data together with data from 1996 disclosed intersite differences and temporal variation in the relationships between HgT, MeHg, and TOC (total organic carbon), reflecting variable sources of HgT, MeHg, and TOC and temporal changes in factors affecting Hg speciation.
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| 10. |
- Regnell, Olof, et al.
(författare)
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Mercury–Selenium Accumulation Patterns in Muscle Tissue of Two Freshwater Fish Species, Eurasian Perch (Perca fluviatilis) and Vendace (Coregonus albula)
- 2022
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Ingår i: Water, Air, and Soil Pollution. - : Springer Science and Business Media LLC. - 0049-6979 .- 1573-2932. ; 233:7
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Tidskriftsartikel (refereegranskat)abstract
- Mercury (Hg) in the form of highly toxic methyl mercury (MeHg) accumulates in aquatic food webs to an extent where it may threaten fish health in many freshwaters. Selenium (Se) mitigates the toxicity of accumulated Hg by forming strong bonds with it, a drawback being diversion of Se from biosynthetic pathways of essential selenoenzymes. We measured Se and Hg in muscle tissue of Eurasian perch (Perca fluviatilis) and vendace (Coregonus albula). For the perch, Se and Hg correlated positively. For the vendace, a positive relationship was seen when the effect of fish size was accounted for. All fish displayed surplus Se (mol Se – mol Hg > 0). For both fish species, the Se molar surplus ((nmol Se – nmol Hg)/g ww) decreased with fish weight. It was higher in the perch than in the vendace and showed the least variation among the small perch (4–34 g). For the large perch (79–434 g), the Se molar surplus decreased with increasing Hg below 0.5 µg Hg but then increased with further Hg increment despite Hg being a negative term in the Se molar surplus. In case the Se molar surplus reflected the weight-specific Se requirement, the latter clearly decreased with increasing fish size for the vendace. This was less clear for the perch because of the strong correlation between Hg and weight. Together, these Se–Hg relationships suggest that Se accumulation was at least partly subject to homeostatic control and responded to the Hg body burden and the Se requirement. Graphical abstract: [Figure not available: see fulltext.]
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