| 1. |
- Balzer, Laura, et al.
(författare)
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Role of formation and decay of seston organic matter in the fate of methylmercury within the water column of a eutrophic lake
- 2023
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Ingår i: Biogeosciences. - 1726-4170 .- 1726-4189. ; 20:7, s. 1459-1472
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Tidskriftsartikel (refereegranskat)abstract
- Anoxic microniches in sinking particles in lakes have been identified as important water phase production zones of monomethylmercury (MeHg). However, the production and decay of MeHg during organic matter (OM) decomposition in the water column and its relation to the total Hg concentration in seston are poorly understood. We investigated total Hg and MeHg in relation to chemical changes in sinking seston and hydrochemical settings in a small and shallow (12 m deep) eutrophic lake during phytoplankton blooms from April to November 2019. The results show that MeHg proportions reach up to 22 % in seston in oxygen super saturation at the water surface and highest values (up to 26 %) at the oxic–suboxic redox boundary. MeHg concentrations were highest in May and November when algal biomass production was low and seston were dominated by zooplankton. Biodilution of MeHg concentrations could not be observed in the months of the highest algal biomass production; instead, MeHg and THg concentrations in seston were comparatively high. During suboxic OM decomposition and with decreasing redox potential (Mn and nitrate reduction), the concentration and proportion of MeHg in seston strongly decreased (<0.5 %), whereas total Hg concentrations show a 3.8- to 26-fold increase with water depth. Here, it remains unclear to which extent biodilution on the one hand and OM decomposition on the other alter the MeHg and THg concentration in seston. Changes in OM quality were most intense within or slightly below the redox transition zone (RTZ). The concentrations of MeHg and THg in seston from the RTZ were comparable to those found in the sediment trap material which integrated the changes in seston composition during the entire sampling period, suggesting that changes in the MeHg and THg content in the hypolimnion below the RTZ are comparatively small. Our study suggests that, in shallow eutrophic lakes, the water phase formation and decomposition of MeHg is intense and controlled by the decomposition of algal biomass and is, assumedly, largely disconnected from Hg methylation in sediments, similar to what has been observed in deep oligotrophic lakes.
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| 2. |
- Baptista-Salazar, Carluvy, et al.
(författare)
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Experiments revealing the formation of refractory methylmercury pools in natural sediments and soils
- 2022
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 328, s. 76-84
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Tidskriftsartikel (refereegranskat)abstract
- Methylation and demethylation of mercury (Hg) are well recognized as processes controlling the concentrations of monomethylmercury (MeHg) in natural environments, and thus the pool of Hg available for biological uptake. In addition, studies have indicated the potential role of refractory MeHg pools (not readily available for demethylation) on the pool of MeHg in, for example, sediments and soils. These studies, however, remain scarce and often the role of refractory MeHg pools is overlooked. Here, we have conducted incubation experiments aiming to quantify refractory MeHg pools in contrasting environments. In our study, sediments (from lakes and brackish seawater sites) and soils (from forests and marshes) were incubated with isotopically enriched Hg tracers (Me201Hg and 198Hg) for up to 6 weeks. To follow the potential formation of refractory MeHg pools, %MeHg (fraction of Hg occurring as MeHg) after the first week of incubation for the added 198Hg and Me201Hg tracers, and ambient Hg was compared. The high %MeHg for the 198Hg tracer compared to the %MeHg of ambient Hg suggests a higher initial availability of added 198Hg in comparison to the ambient Hg in the sediments. For the soils, low %MeHg for the 198Hg tracer suggests low Hg methylation rates. The discrepancy observed between the sediments and soils can be explained by a higher availability of inorganic Hg in the sediments, as suggested by the Hg thermal fractional analysis conducted. The %MeHg steady state for the added Me201Hg tracer remained high (>17%) throughout the experiment, suggesting refractory pools of MeHg to be built-up in all tested sediments and soils. Together, the %MeHg for the added Hg tracers demonstrate that a significant fraction of the MeHg produced in sediments and soils is sequestered into refractory pools not readily available for demethylation. Furthermore, these results show that conditions favoring net methylation in sediments and soil could result in elevated concentrations of MeHg for a significant amount of time (months) even if the conditions favoring Hg net methylation are only temporary.
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| 3. |
- Baptista-Salazar, Carluvy, et al.
(författare)
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Insights into the factors influencing mercury concentrations in tropical reservoir sediments
- 2021
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Ingår i: Environmental Science. - : Royal Society of Chemistry (RSC). - 2050-7887 .- 2050-7895. ; 23:10, s. 1542-1553
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Tidskriftsartikel (refereegranskat)abstract
- Thousands of dams are currently under construction or planned worldwide to meet the growing need for electricity. The creation of reservoirs could, however, lead to conditions that promote the accumulation of mercury (Hg) in surface sediments and the subsequent production of methylmercury (MeHg). Once produced, MeHg can bioaccumulate to harmful levels in organisms. It is unclear to what extent variations in physical features and biogeochemical factors of the reservoir impact Hg accumulation. The objective of this study was to identify key drivers of the accumulation of total Hg (THg) in tropical reservoir sediments. The concentration of THg in all analyzed depth intervals of 22 sediment cores from the five contrasting reservoirs investigated ranged from 16 to 310 ng g(-1) (n = 212, in the different sediment cores, the maximum depth varied from 18 to 96 cm). Our study suggests reservoir size to be an important parameter determining the concentration of THg accumulating in tropical reservoir sediments, with THg ranging up to 50 ng g(-1) in reservoirs with an area exceeding 400 km(2) and from 100 to 200 ng g(-1) in reservoirs with an area less than 80 km(2). In addition to the reservoir size, the role of land use, nutrient loading, biome and sediment properties (e.g., organic carbon content) was tested as potential drivers of THg levels. The principal component analysis conducted suggested THg to be related to the properties of the watershed (high degree of forest cover and low degree of agricultural land use), size and age of the reservoir, water residence time and the levels of nutrients in the reservoir. A direct correlation between THg and tested variables was, however, only observed with the area of the reservoir.
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| 4. |
- Carlsson, Gunilla, et al.
(författare)
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A hundred days in confinement : Doing, being, becoming, and belonging among older people in Sweden during the COVID-19 pandemic
- 2022
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Ingår i: Journal of Occupational Science. - : Informa UK Limited. - 1442-7591 .- 2158-1576. ; 29:3, s. 402-416
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Tidskriftsartikel (refereegranskat)abstract
- Background: When and how people were able to engage in everyday occupations changed suddenly with the coronavirus pandemic. Defined as a risk group due to their age, people 70 years and older in Sweden experienced confinement, as did older adults globally. Aim: To explore how doing, being, becoming, and belonging as dimensions of occupation were manifested in the lives of Swedish people 70 years or older, 100 days into the coronavirus pandemic. Method: Data were elicited through semi-structured interviews with 17 participants (11 women, 6 six men, mean age 76 years), living in ordinary housing in Sweden. Interviews were conducted in June 2020 as part of a larger longitudinal research project. A directed content analysis approach was used to analyse the data based on the occupational dimensions of doing, being, becoming, and belonging. Results: After 100 days of confinement, daily occupations had been changed, and habits and routines disrupted. However, the need to engage in occupations was strong. Participants expressed how they adapted their occupations to the restrictions, but also how their doing affected their well-being, further development, and opportunities for social interactions. Conclusion: The participants, who were older people without any specific diagnosis, reflected upon their daily occupations during an unrehearsed natural experiment when, more than anything else, the social environmental circumstances changed. The analysis elucidates how doing, being, becoming, and belonging is embedded in people’s lives. The study can serve as a foundation to further research on understanding people’s individual needs as occupational beings.
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| 5. |
- Carrasco, Nathalie, et al.
(författare)
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Seasonal riverine inputs may affect diet and mercury bioaccumulation in Arctic coastal zooplankton
- 2024
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Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 906
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Tidskriftsartikel (refereegranskat)abstract
- Climate change driven increases in permafrost thaw and terrestrial runoff are expected to facilitate the mobilization and transport of mercury (Hg) from catchment soils to coastal areas in the Arctic, potentially increasing Hg exposure of marine food webs. The main aim of this study was to determine the impacts of seasonal riverine inputs on land -ocean Hg transport, zooplankton diet and Hg bioaccumulation in an Arctic estuary (Adventfjorden, Svalbard). The Adventelva River was a source of dissolved and particulate Hg to Adventfjorden, especially in June and July during the river's main discharge period. Stable isotope and fatty acid analyses suggest that zooplankton diet varied seasonally with diatoms dominating during the spring phytoplankton bloom in May and with increasing contributions of dinoflagellates in the summer months. In addition, there was evidence of increased terrestrial carbon utilization by zooplankton in June and July, when terrestrial particles contributed substantially to the particulate organic matter pool. Total (TotHg) and methyl Hg (MeHg) concentrations in zooplankton increased from April to August related to increased exposure to riverine inputs, and to shifts in zooplankton diet and community structure. Longer and warmer summer seasons will probably increase riverine runoff and thus Hg exposure to Arctic zooplankton.
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| 6. |
- Fristedt, Sofi, 1969-, et al.
(författare)
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Changes in daily life and wellbeing in adults, 70 years and older, in the beginning of the COVID-19 pandemic
- 2021
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Ingår i: Scandinavian Journal of Occupational Therapy. - : Taylor & Francis. - 1103-8128 .- 1651-2014. ; 29:6, s. 511-521
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: In the beginning of the COVID-19 pandemic, Swedish authorities enforced specific recommendations on social distancing for adults 70 years and older (70+). Day-to-day life changed for 15% of the Swedish population. The aim of the study was to explore how adults 70+ experienced and managed changes in everyday life due to the COVID-19 pandemic and how those changes affected wellbeing at the beginning of the virus outbreak.METHODS: Eleven women and six men, (mean age 76 years), living in ordinary housing, participated in remote semi-structured interviews in April 2020. The interviews were analysed with qualitative content analysis.FINDINGS: The theme Suddenly at risk - '…but it could have been worse' included four categories My world closed down; Negotiations, adaptations and prioritizations to manage staying at home; Barriers and facilitators to sustain occupational participation; and Considerations of my own and other's health and wellbeing emerged from the data analysis.CONCLUSION: Everyday life changes had implications for health and well-being. The participants questioned previous conceptions of meaning in relation to habitual activities, likely leading to consistent occupational changes. However, these long-term effects remain to be explored, and considered to enable older adult's health during the pandemic and beyond.
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| 7. |
- Fristedt, Sofi, et al.
(författare)
-
Suddenly at risk: Older adults’ changes in everyday life early on during the COVID-19 pandemic
- 2022
-
Konferensbidrag (refereegranskat)abstract
- ABSTRACT:Introduction / Rationale: From the onset of the COVID-19 pandemic, social distancing was recommended for adults 70 years and older (70+) in Sweden. From an outside view, they then became deprived of possibilities to engage in meaningful activities. However, as meaning is highly subjective, we need to listen to older adults’ voices to really know.Objectives: To explore how adults 70+ experienced and managed changes in everyday life due to the COVID-19 pandemic and how those changes affected wellbeing at the beginning of the virus outbreak.Method / Approach: Eleven women and six men, (mean age 76 years), living in ordinary housing, participated in remote semi-structured interviews in April and June 2020. The interviews were analysed with qualitative content analysis.Results: An overall theme Suddenly at risk – “…but it could have been worse” and four categories emerged from the data analysis. The participants had to accept some changes summarized in the first category; my world closed down. They described continuous negotiations, adaptations and prioritizations to manage staying at home in the second category, but they also experienced contextual barriers and facilitators to sustain occupational participation as the third category elucidate, where e.g. the shift of seasons facilitated social activities. Their experiences of health and wellbeing varied and are captured in the fourth category, considerations about my own and other’s health and wellbeing.Conclusion: The participants questioned previous conceptions of meaning in relation to habitual activities, likely leading to consistent occupational changes, potentially affecting health and well-bring also beyond the pandemic.
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| 8. |
- Granbom, Marianne, et al.
(författare)
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'Normality in all the abnormality' : Older adults' experiences of holidays and celebrations from the COVID-19 pandemic
- 2024
-
Ingår i: Australian Occupational Therapy Journal. - : John Wiley & Sons. - 1440-1630 .- 0045-0766.
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: The importance of holidays, traditions, and family celebrations to human culture and occupational engagement has been neglected. The aim of this study was to explore how older adults experienced holidays and celebrations with social and physical distancing during the COVID-19 pandemic.METHODS: A secondary analysis was made on data from the At-Risk Study. Seventeen community-living adults (11 women and 6 men) aged 71-87 years, from Sweden participated. They were interviewed remotely four times during the first year of the pandemic. Data were analysed with qualitative content analysis. No consumer/community involvement occurred.FINDINGS: Three categories on how the participants hoped for, planned, decided, adapted, avoided, and experienced holidays and celebrations with social and physical distancing included expectations and preparations in unpredictable times; the constant need for re-evaluation; and almost everything turned out differently.CONCLUSIONS: The desire to celebrate despite pandemic restrictions shows the importance and meaning holidays hold for older adults. Celebrations can be disrupted for many reasons, not only as extreme as the ongoing pandemic. For wellbeing in later life health care, social care, and society need to understand the inherent components and acknowledge ways of supporting participation in occasional events such as holidays, traditions, and family celebrations.
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| 9. |
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| 10. |
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| 11. |
- Hambäck, Peter A., et al.
(författare)
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Tradeoffs and synergies in wetland multifunctionality : A scaling issue
- 2023
-
Ingår i: Science of the Total Environment. - Amsterdam : Elsevier BV. - 0048-9697 .- 1879-1026. ; 862
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Forskningsöversikt (refereegranskat)abstract
- Wetland area in agricultural landscapes has been heavily reduced to gain land for crop production, but in recent years there is increased societal recognition of the negative consequences from wetland loss on nutrient retention, biodiversity and a range of other benefits to humans. The current trend is therefore to re-establish wetlands, often with an aim to achieve the simultaneous delivery of multiple ecosystem services, i.e., multifunctionality. Here we review the literature on key objectives used to motivate wetland re-establishment in temperate agricultural landscapes (provision of flow regulation, nutrient retention, climate mitigation, biodiversity conservation and cultural ecosystem services), and their relationships to environmental properties, in order to identify potential for tradeoffs and synergies concerning the development of multifunctional wetlands. Through this process, we find that there is a need for a change in scale from a focus on single wetlands to wetlandscapes (multiple neighboring wetlands including their catchments and surrounding landscape features) if multiple societal and environmental goals are to be achieved. Finally, we discuss the key factors to be considered when planning for re-establishment of wetlands that can support achievement of a wide range of objectives at the landscape scale.
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| 12. |
- Hsu-Kim, Heileen, et al.
(författare)
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Challenges and opportunities for managing aquatic mercury pollution in altered landscapes
- 2018
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 47:2, s. 141-169
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Tidskriftsartikel (refereegranskat)abstract
- The environmental cycling of mercury (Hg) can be affected by natural and anthropogenic perturbations. Of particular concern is how these disruptions increase mobilization of Hg from sites and alter the formation of monomethylmercury (MeHg), a bioaccumulative form of Hg for humans and wildlife. The scientific community has made significant advances in recent years in understanding the processes contributing to the risk of MeHg in the environment. The objective of this paper is to synthesize the scientific understanding of how Hg cycling in the aquatic environment is influenced by landscape perturbations at the local scale, perturbations that include watershed loadings, deforestation, reservoir and wetland creation, rice production, urbanization, mining and industrial point source pollution, and remediation. We focus on the major challenges associated with each type of alteration, as well as management opportunities that could lessen both MeHg levels in biota and exposure to humans. For example, our understanding of approximate response times to changes in Hg inputs from various sources or landscape alterations could lead to policies that prioritize the avoidance of certain activities in the most vulnerable systems and sequestration of Hg in deep soil and sediment pools. The remediation of Hg pollution from historical mining and other industries is shifting towards in situ technologies that could be less disruptive and less costly than conventional approaches. Contemporary artisanal gold mining has well-documented impacts with respect to Hg; however, significant social and political challenges remain in implementing effective policies to minimize Hg use. Much remains to be learned as we strive towards the meaningful application of our understanding for stakeholders, including communities living near Hg-polluted sites, environmental policy makers, and scientists and engineers tasked with developing watershed management solutions. Site-specific assessments of MeHg exposure risk will require new methods to predict the impacts of anthropogenic perturbations and an understanding of the complexity of Hg cycling at the local scale.
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| 13. |
- Jonsson, C, et al.
(författare)
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Influence of the membrane material on the adsorptive fouling of ultra-filtration membranes
- 1995
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 108:1-2, s. 79-87
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Tidskriftsartikel (refereegranskat)abstract
- The hydrophilic/hydrophobic properties of the membrane material have an important influence on the membrane flux reduction when treating solutions containing hydrophobic solutes. Different methods of measuring the hydrophobic properties of membranes have been evaluated; measurement of the contact angle being the most commonly used method. In this investigation the flux reduction of eight membranes of approximately the same cut-off, but of different materials, was determined and related to the contact angle. A low-molecular weight hydrophobic solute (octanoic acid) was used as foulant. The flux of the hydrophilic membrane was only marginally reduced, whereas the flux reduction of hydrophobic membranes was significant. Membranes of polyvinylidene fluoride had the lowest flux reduction of the hydrophobic membranes. Differences between membranes of the same material (polyethersulfone), but from different manufacturers, were observed. No relation was found between the flux reduction and the contact angle of the membrane, the initial pure water flux or the retention of a hydrophilic macromolecule (PEG20). The pure water flux of two of the hydrophobic membranes increased significantly during the experiments, whereas the pure water flux of the other hydrophobic membranes decreased. A membrane of polyaramide, with a contact angle of the same order of magnitude as the other hydrophobic membranes, behaved as a hydrophilic membrane, with no influence on the flux at concentrations below the solubility limit of the hydrophobic solute, but experienced the most severe flux decline of all the membranes included in the investigation at the solubility limit. Two modified membranes were included in the investigation. The flux reduction of these membranes was not significantly lower than for the corresponding unmodified membranes of the same materials.
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| 14. |
- Jonsson, C, et al.
(författare)
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The influence of degreasing agents used at car washes on the performance of ultrafiltration membranes
- 1995
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Ingår i: Desalination. - : Elsevier BV. - 1873-4464 .- 0011-9164. ; 100:1-3, s. 115-123
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Tidskriftsartikel (refereegranskat)abstract
- The influence of washing chemicals used at car washes on the flux and retention of three ultrafiltration (UF) membranes has been studied. Eleven commercial degreasing agents, two shampoo agents and a wax were included in the investigation. The membrane performance when treating waste water collected at a car wash at different times of the year was also studied. The retention of the different chemicals varied greatly, but there was no significant difference in COD retention among the three UF membranes. The highest flux was observed when treating the alkaline degreasing agents and the shampoo solutions. The flux and COD retention when treating the waste water from the car wash were 30-50 l/m(2) h and 60%, respectively. One of the low-retention degreasing agents was treated by nanofiltration (NF). The retention was significantly higher when using NF, but the COD concentration in the permeate was still too high to allow the permeate to be discharged without further treatment.
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| 15. |
- Jonsson, Sofi, et al.
(författare)
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Arctic methylmercury cycling
- 2022
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 850
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic mercury (Hg) undergoes long-range transport to the Arctic where some of it is transformed into methylmercury (MeHg), potentially leading to high exposure in some Arctic inhabitants and wildlife. The environmental exposure of Hg is determined not just by the amount of Hg entering the Arctic, but also by biogeochemical and ecological processes occurring in the Arctic. These processes affect MeHg uptake in biota by regulating the bioavailability, methylation and demethylation, bioaccumulation and biomagnification of MeHg in Arctic ecosystems. Here, we present a new budget for pools and fluxes of MeHg in the Arctic and review the scientific advances made in the last decade on processes leading to environmental exposure to Hg. Methylation and demethylation are key processes controlling the pool of MeHg available for bioaccumulation. Methylation of Hg occurs in diverse Arctic environments including permafrost, sediments and the ocean water column, and is primarily a process carried out by microorganisms. While microorganisms carrying the hgcAB gene pair (responsible for Hg methylation) have been identified in Arctic soils and thawing permafrost, the formation pathway of MeHg in oxic marine waters remains less clear. Hotspots for methylation of Hg in terrestrial environments include thermokarst wetlands, ponds and lakes. The shallow sub-surface enrichment of MeHg in the Arctic Ocean, in comparison to other marine systems, is a possible explanation for high MeHg concentrations in some Arctic biota. Bioconcentration of aqueous MeHg in bacteria and algae is a critical step in the transfer of Hg to top predators, which may be dampened or enhanced by the presence of organic matter. Variable trophic position has an important influence on MeHg concentrations among populations of top predator species such as ringed seal and polar bears distributed across the circumpolar Arctic. These scientific advances highlight key processes that affect the fate of anthropogenic Hg deposited to Arctic environments.
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| 16. |
- Jonsson, Sofi, et al.
(författare)
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Differentiated availability of geochemical mercury pools controls methylmercury levels in estuarine sediment and biota
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 4624-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 17. |
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| 18. |
- Jonsson, Sofi, et al.
(författare)
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Dimethylmercury Formation Mediated by Inorganic and Organic Reduced Sulfur Surfaces
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Underlying formation pathways of dimethylmercury ((CH3)2Hg) in the ocean are unknown. Early work proposed reactions of inorganic Hg (Hg II) with methyl cobalamin or of dissolved monomethylmercury (CH3Hg) with hydrogen sulfide as possible bacterial mediated or abiotic pathways. A significant fraction (up to 90%) of CH3Hg in natural waters is however adsorbed to reduced sulfur groups on mineral or organic surfaces. We show that binding of CH3Hg to such reactive sites facilitates the formation of (CH3)2 Hg by degradation of the adsorbed CH3Hg. We demonstrate that the reaction can be mediated by different sulfide minerals, as well as by dithiols suggesting that e.g. reduced sulfur groups on mineral particles or on protein surfaces could mediate the reaction. The observed fraction of CH3Hg methylated on sulfide mineral surfaces exceeded previously observed methylation rates of CH3Hg to (CH3)2 Hg in seawaters and we suggest the pathway demonstrated here could account for much of the (CH3)2 Hg found in the ocean.
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| 19. |
- Jonsson, Sofi, et al.
(författare)
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Distribution of total mercury and methylated mercury species in Central Arctic Ocean water and ice
- 2022
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203 .- 1872-7581. ; 242
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Tidskriftsartikel (refereegranskat)abstract
- The central Arctic Ocean remains largely unexplored when it comes to the presence and cycling of mercury and its methylated forms including mono- and dimethylmercury (MMeHg and DMeHg, respectively). In this study, we quantified total Hg (HgT) and methylated Hg species in seawater, ice cores, snow, brine, and water from melt ponds collected during the SWEDARCTIC 2016 expedition to the Amerasian and Eurasian side of the Lomonosov Ridge. In the water column, concentrations of HgT, MMeHg and DMeHg ranged from 0.089 to 1.5 pM, <25 to 520 fM and from <1.6 to 160 fM, respectively. HgT was enriched in surface waters while MMeHg and DMeHg were low at the surface (i.e. in the polar mixed layer) and enriched at a water depth of around 200–400 m. A 1:2 ratio of DMeHg to MMeHg was observed in the water column suggesting a lower ratio in the central parts of the Arctic Ocean than what has previously been reported from other parts of the Arctic Ocean. At the ice stations, average HgT ranged from 0.97 ± 1.2 pM in the ice cores to 27 ± 17 pM in melt pond waters and average MeHgT (total MeHg) from 28 ± 15 fM in brine to 130 ± 18 fM in melt pond water. The HgT observed in melt ponds and brine was an order of magnitude greater than HgT observed in surface waters and HgT in the upper part of the ice-cores was ~4–8 times higher HgT in comparison to lower layers. Our study suggests that ice may act as a source of HgT to surface waters but not to be a likely source of the methylated Hg forms. Unlike elemental Hg, DMeHg did not enrich in surface waters covered by ice. Concentrations of DMeHg observed in the ice cores and other samples collected from the ice stations were low, suggesting ice to not act as a source of DMeHg to the atmosphere nor to surface waters.
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| 20. |
- Jonsson, Sofi, 1984-, et al.
(författare)
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Geochemical and Dietary Drivers of Mercury Bioaccumulation in Estuarine Benthic Invertebrates
- 2022
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 56:14, s. 10141-10148
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Tidskriftsartikel (refereegranskat)abstract
- Sediments represent the main reservoir of mercury (Hg) in aquatic environments and may act as a source of Hg to aquatic food webs. Yet, accumulation routes of Hg from the sediment to benthic organisms are poorly constrained. We studied the bioaccumulation of inorganic and methylmercury (HgII and MeHg, respectively) from different geochemical pools of Hg into four groups of benthic invertebrates (amphipods, polychaetes, chironomids, and bivalves). The study was conducted using mesocosm experiments entailing the use of multiple isotopically enriched Hg tracers and simulation of estuarine systems with brackish water and sediment. We applied different loading regimes of nutrients and terrestrial organic matter and showed that the vertical localization and the chemical speciation of HgII and MeHg in the sediment, in combination with the diet composition of the invertebrates, consistently controlled the bioaccumulation of HgII and MeHg into the benthic organisms. Our results suggest a direct link between the concentration of MeHg in the pelagic planktonic food web and the concentration of MeHg in benthic amphipods and, to some extent, in bivalves. In contrast, the quantity of MeHg in benthic chironomids and polychaetes seems to be driven by MeHg accumulation via the benthic food web. Accounting for these geochemical and dietary drivers of Hg bioaccumulation in benthic invertebrates will be important to understand and predict Hg transfer between the benthic and the pelagic food web, under current and future environmental scenarios.
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| 21. |
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| 22. |
- Jonsson, Sofi, 1984-, et al.
(författare)
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Mercury methylation rates for geochemically relevant HgII species in sediments
- 2012
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 46:21, s. 11653-11659
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 23. |
- Jonsson, Sofi, 1984-, et al.
(författare)
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Substantial emission of gaseous monomethylmercury from contaminated water-sediment microcosms
- 2010
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 44:1, s. 278-283
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Tidskriftsartikel (refereegranskat)abstract
- 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).
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| 24. |
- Jonsson, Sofi, et al.
(författare)
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Terrestrial discharges mediate trophic shifts and enhance methylmercury accumulation in estuarine biota
- 2017
-
Ingår i: Science Advances. - : American association for the advancement of science. - 2375-2548. ; 3:1
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 25. |
- Jonsson, Sofi, 1984-
(författare)
-
Unraveling the importance of solid and adsorbed phase mercury speciation for methylmercury formation, evasion and bioaccumulation
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Monomethylmercury, MeHg, is formed under anoxic conditions in waters, sediments and soils and then bioaccumulated and biomagnified in aquatic food webs, negatively effecting both human and wildlife health. It is generally accepted that precipitation of mercury, Hg, and adsorption of Hg to e.g. organic matter and mineral surfaces are important processes limiting the reactivity of Hg mobilized in the environment by natural and anthropogenic activities. However, knowledge concerning the role of different solid and adsorbed chemical forms of Hg for MeHg formation, evasion and bioaccumulation is missing. Such information is vital for the understanding of environmental processes controlling MeHg formation and bioaccumulation, as well as for predicting how changes in e.g. loading rates of atmospheric Hg and the outcome of climate change scenarios and anthropogenic land use could alter Hg concentrations in biota.In this thesis, a novel experimental approach, using isotopically enriched solid and adsorbed phases of inorganic Hg, HgII, as tracers, was developed. Using this approach, we successfully determined rates of MeHg formation from solid and adsorbed Hg species in sediment slurries and in mesocosm systems under conditions closely resembling those in field. We conclude that the solid/adsorbed phase speciation of HgII is a major controlling factor for MeHg net formation rates. Microcosm experiments revealed that newly formed MeHg was a major contributor to the evasion of MeHg from the water‒sediment system, emphasizing the importance of MeHg formation rate, rather than MeHg concentration, in the sediment for this process. From mesocosm systems, we provide experimental evidence, as well as quantitate data, for that terrestrial and atmospheric sources of HgII and MeHg are more available for methylation and bioaccumulation processes than HgII and MeHg stored and formed in sediments. This suggests that the contribution from terrestrial and atmospheric sources to the accumulation of Hg in fish may have been underestimated. As a consequence, in regions where climate change is expected to further increase land runoff, terrestrial MeHg sources may have even higher negative effects on biota than previously thought. Data and concepts presented in this thesis lay the basis for unprecedented in-depth modeling of processes in the Hg biogeochemical cycle that will improve our understanding and the predicting power on how aquatic ecosystems may respond to environmental changes or differences in loading rates for atmospheric Hg.
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| 26. |
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| 27. |
- Jönsson, Ann-Sofi, et al.
(författare)
-
Treatment of paper coating colour effluents by membrane filtration
- 1996
-
Ingår i: Desalination. - : Elsevier BV. - 1873-4464 .- 0011-9164. ; 105:3, s. 263-276
-
Tidskriftsartikel (refereegranskat)abstract
- Dilute coating colour effluents are created during the coating of paper and board. After treating the colour effluents with ultrafiltration, the retentate can be reused as coating colour and the permeate can replace fresh water. At the same time, the load on the external treatment plant is reduced. In this investigation, pilot-plant experiments were performed at a paper mill. A high and steady flux, 120 l/m(2) h, was achieved at a colour concentration of 10-15%. The flux at 40% was lower but steady, 50 l/m(2) h. The membrane performance when treating five coating colours with varying composition was studied in laboratory experiments. The composition of the colour had a significant influence on the membrane performance. A colour containing starch exhibited the lowest flux and the lowest COD retention of the colours included in the study, while a colour in which the clay had been replaced by CaCO3 exhibited the highest final concentration of 60%.
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| 28. |
- Kakar, Allauddin, et al.
(författare)
-
Elevated concentrations of mercury and methylmercury in the Gadani shipbreaking area, Pakistan
- 2021
-
Ingår i: Marine Pollution Bulletin. - : Elsevier BV. - 0025-326X .- 1879-3363. ; 165
-
Tidskriftsartikel (refereegranskat)abstract
- Gadani shipbreaking area, Pakistan, is the world's third largest shipbreaking unit. However, to date, only a few studies on the environmental impacts of the industry, including mercury (Hg) pollution, have been conducted. To address this, concentrations of total Hg (HgT) and methylmercury (MeHg) were measured in surface sediments collected from the Gadani shipbreaking area as well as a local reference area. The highest concentrations of HgT and MeHg (median +/- interquartile range) were detected in samples from the beach at the yard zone (HgT: 270 +/- 230 mu g kg(-1), MeHg: 0.65 +/- 0.69 mu g kg(-1)), followed by sediment samples from the inter/sub-tidal zone where ships are dismantled (HgT: 20 +/- 5.8 mu g kg(-1), MeHg: 0.043 +/- 0.016 mu g kg(-1)). These concentrations were on average 4-50 and 3-30 times greater than the concentrations of HgT and MeHg, respectively, observed in the reference area. Capsule: Elevated concentrations of total and methylated mercury observed in the Gadani Shipbreaking area sediments.
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| 29. |
- Lian, Peng, et al.
(författare)
-
Mechanistic Investigation of Dimethylmercury Formation Mediated by a Sulfide Mineral Surface
- 2021
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 125:24, s. 5397-5405
-
Tidskriftsartikel (refereegranskat)abstract
- Mercury (Hg) pollution is a global environmental problem. The abiotic formation of dimethylmercury (DMeHg) from monomethylmercury (MMeHg) may account for a large portion of DMeHg in oceans. Previous experimental work has shown that abiotic formation of DMeHg from MMeHg can be facilitated by reduced sulfur groups on sulfide mineral surfaces. In that work, a mechanism was proposed in which neighboring MMeHg moieties bound to sulfide sites on a mineral surface react through an SN2-type mechanism to form DMeHg and incorporate the remaining Hg atoms into the mineral surface. Here, we perform density functional theory calculations to explore the mechanisms of DMeHg formation on the 110 surface of a CdS(s) (hawleyite) nanoparticle. We show that coordination of MMeHg substituents to adjacent reduced sulfur groups protruding from the surface indeed facilitates DMeHg formation and that the reaction proceeds through direct transmethylation from one MMeHg substituent to another. Coordination of Hg by multiple S atoms provides a transition-state stabilization and activates a C–Hg bond for methyl transfer. In addition, solvation effects play an important role in the surface reconstruction of the nanoparticle and in decreasing the energetic barrier for DMeHg formation relative to the corresponding reaction in vacuo.
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| 30. |
- Liem-Nguyen, Van, et al.
(författare)
-
Effects of Nutrient Loading and Mercury Chemical Speciation on the Formation and Degradation of Methylmercury in Estuarine Sediment
- 2016
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 50:13, s. 6983-6990
-
Tidskriftsartikel (refereegranskat)abstract
- Net formation of methylmercury (MeHg) in sediments is known to be affected by the availability of inorganic divalent mercury (HgII) and by the activities of HgII methylating and MeHg demethylating bacteria. Enhanced autochthonous organic matter deposition to the benthic zone, following increased loading of nutrients to the pelagic zone, has been suggested to increase the activity of HgII methylating bacteria and thus the rate of net methylation. However, the impact of increased nutrient loading on the biogeochemistry of mercury (Hg) is challenging to predict as different geochemical pools of Hg may respond differently to enhanced bacterial activities. Here, we investigate the combined effects of nutrient (N and P) supply to the pelagic zone and the chemical speciation of HgII and of MeHg on MeHg formation and degradation in a brackish sediment-water mesocosm model ecosystem. By use of Hg isotope tracers added in situ to the mesocosms or ex situ in incubation experiments, we show that the MeHg formation rate increased with nutrient loading only for HgII tracers with a high availability for methylation. Tracers with low availability did not respond significantly to nutrient loading. Thus, both microbial activity (stimulated indirectly through plankton biomass production by nutrient loading) and HgII chemical speciation were found to control the MeHg formation rate in marine sediments.
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| 31. |
- Liem-Nguyen, Van, et al.
(författare)
-
Spatial patterns and distributional controls of total and methylated mercury off the Lena River in the Laptev Sea sediments
- 2022
-
Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203 .- 1872-7581. ; 238
-
Tidskriftsartikel (refereegranskat)abstract
- A warmer climate is predicted to accelerate the export of mercury (Hg) from Siberian rivers to the Arctic Ocean, yet there is a dearth of process-oriented studies on the speciation and fate of Hg in the shelf sea system. Here, we present data on total Hg (HgT) and methylmercury (MeHg) in Laptev Sea surface sediments along a cross-shelf transect starting at the mouth of the Lena River. Concentrations of HgT along the 330 km cross-shelf transect ranged within a fairly narrow span from 480 to 150 pmol g(-1) d.w., while concentrations of MeHg decreased one hundredfold from 13 pmol g(-1) d.w. near the Lena river to 0.095 pmol g(-1) d.w. in the more distall stations. The highest concentrations of HgT and MeHg were observed close to the river delta and were associated with a high supply of organic carbon (OC). Enrichment of the OC normalized HgT concentration (HgTOC) and depletion of the OC normalized MeHg concentration (MeHgOC) across the shelf suggests bulk OC content to not be the only driver of the HgT and MeHg spatial distributions. Based on correlations observed between HgTOC and MeHgOC and proxies for sediment physics and organic matter pools we suggest the spatial distribution of Hg and MeHg to also be influenced by hydrodynamic sorting of riverine-derived material. For MeHg, depletion of the MeHgOC across the shelf is likely driven by the trapping of terrestrial MeHg in sediments close to the river delta before it is degraded in the water column.
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| 32. |
- Maryam, Afsheen, et al.
(författare)
-
Trace Metals in Sediment and Peat Cores of Remote Glacial Lakes in Hindu Kush, Karakoram, and Himalayan Region of Pakistan
- 2024
-
Ingår i: Water, Air and Soil Pollution. - 0049-6979 .- 1573-2932. ; 235:5
-
Tidskriftsartikel (refereegranskat)abstract
- Hindukush (HK), Karakoram (KK), and Himalayan (HM) ranges (collectively called HKH), an extension of the Tibetan plateau, are sensitive areas for mercury (Hg) and other trace metals (TMs) contamination. These metals reach remote regions via long-range atmospheric transport from distant transboundary pollution sources, whereas local emissions, physiography, and climatic properties of alpine regions cause further enrichment of Hg and other TMs. Little is known about the chemical cycling of Hg and other TMs in the HKH region, which was investigated in the current study. Sediment and peat cores were taken from 10 remote lakes of the region, comprising three sediments and one peat core each from HM and KK, and two sediment cores from HK region. The mean concentration of total Hg in HM lakes was 13.08 µg/g, 8.46 µg/g in HK lakes, and 4.65 µg/g in KK lakes. Other metals, including iron (Fe), manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), zinc (Zn), cadmium (Cd), arsenic (As), and selenium (Se), were also investigated in these cores. The mean concentrations of these metals in all three ranges were observed to be in decreasing order of Fe > Mn > Zn > Ni > Cr > As > Pb > Se > Cd. Overall, HM lakes were found to be highly enriched in Hg and other TMs, compared to KK and HK lakes. Both the mass burial rate (MBR) and mass burial flux (MBF) of Hg and other TMs were in decreasing order of HM > KK > HK. As a result of these findings, Hg might pose a potential risk within the remote lakes of HKH; therefore, further studies are highly recommended to understand the geochemistry, source apportionment, and bioaccumulation of Hg and other toxic metals in this pristine region.
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| 33. |
- Mazrui, N. M., et al.
(författare)
-
Enhanced availability of mercury bound to dissolved organic matter for methylation in marine sediments
- 2016
-
Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 194, s. 153-162
-
Tidskriftsartikel (refereegranskat)abstract
- The forms of inorganic mercury (HgII) taken up and methylated by bacteria in sediments still remain largely unknown. From pure cultures studies, it has been suggested that dissolved organic matter (DOM) may facilitate the uptake either by acting as a shuttle molecule, transporting the HgII atom to divalent metal transporters, or by binding HgII and then being transported into the cell as a carbon source. Enhanced availability of Hg complexed to DOM has however not yet been demonstrated in natural systems. Here, we show that HgII complexed with DOM of marine origin was up to 2.7times more available for methylation in sediments than HgII added as a dissolved inorganic complex (HgII(aq)). We argue that the DOM used to complex HgII directly facilitated the bacterial uptake of HgII whereas the inorganic dissolved HgII complex adsorbed to the sediment matrix before forming bioavailable dissolved HgII complexes. We further demonstrate that differences in net methylation in sediments with high and low organic carbon content may be explained by differences in the availability of carbon to stimulate the activity of Hg methylating bacteria rather than, as previously proposed, be due to differences in HgII binding capacities between sediments. © 2016 Elsevier Ltd
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| 34. |
- Persson, A, et al.
(författare)
-
Conversion of sodium lactate to lactic acid with water-splitting electrodialysis
- 2001
-
Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 94:3, s. 197-211
-
Tidskriftsartikel (refereegranskat)abstract
- The conversion of sodium lactate to lactic acid with water-splitting electrodialysis was investigated. One way of reducing the power consumption is to add a conductive layer to the acid compartment. Doing this reduced the power consumption by almost 50% in a two-compartment cell, whereas the electric current efficiency was not affected at all. Three different solutions were treated in the electrodialysis unit: a model solution with 70 g/L of sodium lactate and a fermentation broth that had been prefiltered two different ways. The fermentation broth was either filtered in an open ultrafiltration membrane (cut-off of 100,000 Dalton) in order to remove the microorganisms or first filtered in the open ultrafiltration membrane and then in an ultrafiltration membrane with a cut-off of 2000 Dalton to remove most of the proteins. The concentration of sodium lactate in the fermentation broth was 70 g/L, as well. Organic molecules present in the broth (peptides and similar organic material) fouled the membranes and, therefore, increased power consumption. Power consumption increased more when permeate from the more open ultrafiltration membrane was treated in the electrodialysis unit than when permeate from the membrane with the lower cut-off was treated, since there was a higher amount of foulants in the former permeate. However, the electrodialysis membranes could be cleaned efficiently with a 0.1 M sodium hydroxide solution.
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| 35. |
- Skogsberg, Emelie, et al.
(författare)
-
Seasonal pollutant levels in littoral high-Arctic amphipods in relation to food sources and terrestrial run-off
- 2022
-
Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491 .- 1873-6424. ; 306
-
Tidskriftsartikel (refereegranskat)abstract
- Increasing terrestrial run-off from melting glaciers and thawing permafrost to Arctic coastal areas is expected to facilitate re-mobilization of stored legacy persistent organic pollutants (POPs) and mercury (Hg), potentially increasing exposure to these contaminants for coastal benthic organisms. We quantified chlorinated POPs and Hg concentrations, lipid content and multiple dietary markers, in a littoral deposit-feeding amphipod Gammarus setosus and sediments during the melting period from April to August in Adventelva river estuary in Svalbard, a Norwegian Arctic Aarchipelago. There was an overall decrease in concentrations of ∑POPs from April to August (from 58 ± 23 to 13 ± 4 ng/g lipid weight; lw), Hg (from 5.6 ± 0.7 to 4.1 ± 0.5 ng/g dry weight; dw) and Methyl Hg (MeHg) (from 5 ± 1 to 0.8 ± 0.7 ng/g dw) in G. setosus. However, we observed a seasonal peak in penta- and hexachlorobenzene (PeCB and HCB) in May (2.44 ± 0.3 and 23.6 ± 1.7 ng/g lw). Sediment concentrations of POPs and Hg (dw) only partly correlated with the contaminant concentrations in G. setosus. Dietary markers, including fatty acids and carbon and nitrogen stable isotopes, indicated a diet of settled phytoplankton in May–July and a broader range of carbon sources after the spring bloom. Phytoplankton utilization and chlorobenzene concentrations in G. setosus exhibited similar seasonal patterns, suggesting a dietary uptake of chlorobenzenes that is delivered to the aquatic environment during spring snowmelt. The seasonal decrease in contaminant concentrations in G. setosus could be related to seasonal changes in dietary contaminant exposure and amphipod ecology. Furthermore, this decrease implies that terrestrial run-off is not a significant source of re-mobilized Hg and legacy POPs to littoral amphipods in the Adventelva river estuary during the melt season.
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| 36. |
- Tarbier, Brittany, et al.
(författare)
-
Permafrost Thaw Increases Methylmercury Formation in Subarctic Fennoscandia
- 2021
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 55:10, s. 6710-6717
-
Tidskriftsartikel (refereegranskat)abstract
- Methylmercury (MeHg) forms in anoxic environments and can bioaccumulate and biomagnify in aquatic food webs to concentrations of concern for human and wildlife health. Mercury (Hg) pollution in the Arctic environment may worsen as these areas warm and Hg, currently locked in permafrost soils, is remobilized. One of the main concerns is the development of Hg methylation hotspots in the terrestrial environment due to thermokarst formation. The extent to which net methylation of Hg is enhanced upon thaw is, however, largely unknown. Here, we have studied the formation of Hg methylation hotspots using existing thaw gradients at five Fennoscandian permafrost peatland sites. Total Hg (HgT) and MeHg concentrations were analyzed in 178 soil samples from 14 peat cores. We observed 10 times higher concentrations of MeHg and 13 times higher %MeHg in the collapse fen (representing thawed conditions) as compared to the peat plateau (representing frozen conditions). This suggests significantly greater net methylation of Hg when thermokarst wetlands are formed. In addition, we report HgT to soil organic carbon ratios representative of Fennoscandian permafrost peatlands (median and interquartile range of 0.09 +/- 0.07 mu g HgT g(-1) C) that are of value for future estimates of circumpolar HgT stocks.
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| 37. |
- West, Johannes, 1991-
(författare)
-
Degradation Pathways of Dimethylmercury in Natural Waters
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mercury (Hg) is a naturally occurring toxic trace metal whose release into the environment has been (and still is) exacerbated by human activities. The bioavailability of Hg is tied to its chemical speciation, with monomethylmercury (MMHg) being the primary form of Hg that bioaccumulates and biomagnifies. At the top of some food webs, MMHg can reach harmful levels. In addition to MMHg, a second methylated Hg species, dimethylmercury (DMHg), is found in aquatic environments. Dimethylmercury is especially abundant in the oceans, where it could potentially act as an important source of MMHg. The stability of DMHg in natural waters and which biogeochemical processes may be important for its degradation are poorly constrained. This knowledge gap could partially be related to the extreme toxicity and the volatility of DMHg, making it challenging to handle in the laboratory.Through experimental studies, this thesis work has aimed to increase the understanding of DMHg cycling in the aquatic environment. Focusing on the stability and degradation of DMHg, abiotic pathways of DMHg degradation were explored. In Paper I, DMHg degradation via a novel sulfide-mediated pathway was demonstrated for both particulate and dissolved sulfide phases. Key aspects of the process were investigated through the manipulation of pH and DMHg:S ratios. In Paper II, the previously disputed process of aqueous photochemical decomposition of DMHg was confirmed for various natural and artificial water types. This process was studied further in Paper III by investigating the impact of dissolved organic matter and chloride on DMHg photodecomposition rates and the involvement of photochemically produced reactive intermediates. Monomethylmercury was the primary product of both sulfide-mediated decomposition and photodecomposition of DMHg. Rate calculations (Paper I and II) and comparison with MMHg photodecomposition (Paper II and III) confirm that both sulfide-mediated decomposition and aqueous photodecomposition of DMHg could be environmentally significant. Paper IV presents methods and considerations for laboratory work with DMHg, providing insights into both experimental and analytical aspects. This work demonstrates that DMHg can be analyzed together with MMHg and that significant safety risks of working with DMHg can be largely avoided. These insights are important as future work on DMHg is necessary to elucidate its role in aqueous Hg cycling in general and for MMHg cycling in particular.
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| 38. |
- West, Johannes, et al.
(författare)
-
Dimethylmercury Degradation by Dissolved Sulfide and Mackinawite
- 2020
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 54:21, s. 13731-13738
-
Tidskriftsartikel (refereegranskat)abstract
- Potential degradation pathways of dimethylmercury (DMHg) remain as one of the critical knowledge gaps in the marine biogeochemical cycle of mercury (Hg). Although Hg is known to be highly reactive with reduced sulfur, demethylation of DMHg in the presence of sulfide has until now remained experimentally untested. Here, we provide the first experimental support for demethylation of DMHg to monomethylmercury (MMHg) in the presence of both dissolved sulfide and mackinawite (FeS(s)m). The degradation of DMHg was shown to be pH dependent, with higher demethylation rates at pH 9 than pH 5. At room temperature and environmentally relevant DMHg to sulfide molar ratios, we observed demethylation rates up to 0.05 d–1. When comparing the number of active sites available, FeS(s)m was found to have a higher capacity to demethylate DMHg, in comparison with dissolved sulfide. Our study suggests that dissolved sulfide and FeS(s)m mediated demethylation of DMHg may act as a sink for DMHg, and a potential source of MMHg, in aquatic systems.
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| 39. |
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| 40. |
- West, Johannes, 1991-, et al.
(författare)
-
Dimethylmercury in natural waters—analytical and experimental considerations
- 2023
-
Ingår i: Limnology and Oceanography. - 1541-5856. ; 21:12, s. 837-846
-
Tidskriftsartikel (refereegranskat)abstract
- Mono- and dimethylmercury (MMHg and DMHg, respectively) are the two primary organic forms of mercury (Hg) found in natural waters. While experimental approaches to characterize the environmental behavior of MMHg and inorganic forms of Hg are widely used today, few laboratories conduct experimental studies entailing the use of DMHg. In this paper, we have evaluated and developed different analytical and experimental approaches to quantify and use DMHg in laboratory studies. We demonstrate that DMHg can be analyzed from samples where MMHg is derivatized using sodium tetraethyl borate and where the matrix effects of dissolved sulfide are masked using copper sulfate. Tests, where the calibration curves of MMHg and DMHg were used, showed that MMHg may be used to calibrate for DMHg. For the pre-concentration of DMHg, both traps filled with Tenax® TA and Bond Elut ENV were found suitable. We observed good recoveries of DMHg added to different types of natural waters or purified water containing aquarium salt, sodium chloride and dissolved sulfide, iron sulfide, and cadmium sulfide at DMHg : sulfide molar ratios > 10−6. In addition to evaluating these analytical aspects, we present suitable subsampling techniques for DMHg-containing solutions, the recovery of DMHg when filtering DMHg through different types of filters, and experimental data on the long-term stability of DMHg added to different types of waters and stored at different temperatures. Finally, we present and discuss a new synthetization protocol for preparing aqueous solutions containing DMHg free of organic solvents and where handling DMHg in a pure form is prevented.
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| 41. |
|
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| 42. |
- West, Johannes, et al.
(författare)
-
Photochemical Degradation of Dimethylmercury in Natural Waters
- 2022
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 56:9, s. 5920-5928
-
Tidskriftsartikel (refereegranskat)abstract
- Photochemical demethylation of dimethylmercury (DMHg) could potentially be an important source of monomethylmercury (MMHg) in sunlit water. Whether or not DMHg is photochemically degraded when dissolved in water is, however, debated. While an early study suggested DMHg dissolved in natural waters to readily degrade, later work claimed DMHg to be stable in seawater under natural sunlight and that early observations may be due to experimental artifacts. Here, we present experimental data showing that DMHg is readily degraded by photochemical processes in different natural waters (including water from a DOC-rich stream, the Baltic Sea, and the Arctic Ocean) as well as in artificial seawater and purified water. For most of the waters, the degradation rate constant (kd) for DMHg measured in indoor experiments exceeded, or was close to, the kd observed for MMHg. Outdoor incubations of DMHg in purified water and Arctic Ocean surface water further confirmed that DMHg is photochemically degraded under natural sunlight. Our study shows that DMHg is photochemically degraded in a range of natural waters and that this process may be a source of MMHg in sunlit waters where the supply or formation of DMHg is sufficient.
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| 43. |
- Wiederhold, Jan G., et al.
(författare)
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Mercury Isotope Signatures in Contaminated Sediments as a Tracer for Local Industrial Pollution Sources
- 2015
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 49:1, s. 177-185
-
Tidskriftsartikel (refereegranskat)abstract
- Mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) may cause characteristic isotope signatures of different mercury (Hg) sources and help understand transformation processes at contaminated sites. Here, we present Hg isotope data of sediments collected near industrial pollution sources in Sweden contaminated with elemental liquid Hg (mainly chlor-alkali industry) or phenyl-Hg (paper industry). The sediments exhibited a wide range of total Hg concentrations from 0.86 to 99 mu g g(-1)), consisting dominantly of organically-bound Hg and smaller amounts of sulfide-bound Hg. The three phenyl-Hg sites showed very similar Hg isotope signatures (MDF delta Hg-202: -0.2 parts per thousand to -0.5 parts per thousand; MIF Delta Hg-199: -0.05 parts per thousand to -0.10 parts per thousand). In contrast, the four sites contaminated with elemental Hg displayed much greater variations (delta Hg-202: -2.1 parts per thousand to 0.6 parts per thousand; Delta Hg-199: -0.19 parts per thousand to 0.03 parts per thousand) but with distinct ranges for the different sites. Sequential extractions revealed that sulfide-bound Hg was in some samples up to 1 parts per thousand heavier in delta Hg-202 than organically-bound Hg. The selectivity of the sequential extraction was tested on standard materials prepared with enriched Hg isotopes, which also allowed assessing isotope exchange between different Hg pools. Our results demonstrate that different industrial pollution sources can be distinguished on the basis of Hg isotope signatures, which may additionally record fractionation processes between different Hg pools in the sediments.
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| 44. |
- Åkerblom, Staffan, et al.
(författare)
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Formation and mobilization of methylmercury across natural and experimental sulfur deposition gradients
- 2020
-
Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491 .- 1873-6424. ; 263
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Tidskriftsartikel (refereegranskat)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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