Browsing by Subject "Mercury"
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Item Bench Scale Tests to Separate Mercury from Wet‐Scrubber Solids from Taconite Plants(University of Minnesota Duluth, 2007) Benner, Blair RItem Characterization and modeling of materials responsible for planetary crustal magnetism(2016-08) Strauss, BeckyEarth and Mercury are the only terrestrial planets in our solar system with present-day magnetic dipole fields generated by internal dynamo systems. In contrast, Mars and the Moon show evidence of past dipole fields in the form of crustal magnetic anomalies; to hold measurable magnetizations, crustal materials must have been exposed to an applied field. While the physical principles of magnetic recording are consistent between terrestrial planets, the particular conditions at each planet control the mechanisms by which crustal materials may be magnetized and limit the types of minerals that can retain magnetic remanence. As the suite of magnetic materials used for studies of remanence expands, the need for new methods follows. The integration of rock magnetic techniques with microscopy and chemical analyses enables the reconstruction of increasingly comprehensive narratives of remanence acquisition and alteration, even in materials that are challenging to study using traditional methods. This thesis demonstrates the utility of a materials approach to rock magnetism by applying techniques designed for terrestrial use in a planetary context. The first of two case studies focuses on calcite cave deposits as a means to demonstrate how novel techniques can be used to unlock previously inaccessible archives of magnetic information. Tandem magnetic and microscopic analyses improve our understanding of the rock magnetic properties of weakly magnetic stalagmites and their potential for paleomagnetic research, as well as illuminating the pathways of remanence acquisition in cave systems. The second case study addresses the magnetic anomalies recently detected by the MESSENGER orbiter at Mercury. These anomalies are consistent with remanence acquired in a dipole field. However, in the absence of physical samples, the types of magnetic minerals that could be holding remanence in Mercury’s hot, highly reducing surface environment have not yet been determined. Orbital data is combined with fundamental rock magnetic principles to constrain the magnetic mineralogy of Mercury and to propose mechanisms of magnetization and remagnetization in the lithosphere.Item The Effect Of Climate Change On Mercury In Boreal Peatlands(2023-09) Pierce, CarolineMercury is a ubiquitous pollutant that accumulates in peatlands, an ecosystem highly sensitive to climate change. Methylmercury (MeHg) is a neurotoxin that is capable of biomagnifying in food webs. We examined the effects of increasing temperature and elevated atmospheric carbon dioxide (CO2) on the concentration of total mercury (THg) and MeHg in peatland soil. This research was performed at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment, an ecosystem-scale manipulation in an ombrotrophic bog in northern Minnesota, USA, which includes five temperature levels (ambient plus above- and below-ground warming), with ambient or enhanced CO2 concentration. Increased temperature led to decreased MeHg concentrations in peat and increased THg and MeHg in porewaters. This decrease in peat MeHg, and increases in THg and MeHg in porewater could be caused by more rapid decomposition of the peat leading to mercury mobilization, increased methylation/demethylation rates, or increased gaseous mercury emission. The response to elevated atmospheric CO2 was limited to the surface depths of peat. Total mercury and MeHg decreased in the peat and increased in the porewater. There are no known direct effects of CO2 on mercury cycling so this finding is likely due to changes in other response variables such as the lowering of the water table or changes in the proportion of different plant species. Overall, we observed that temperature and CO2 had significant but subtle effects on THg and MeHg retention in peat. Our findings indicate that mercury concentrations in peat may decrease with climate change which may shift the system from a mercury sink to a mercury source.Item Identification of Methylmercury Export Hotspots in an Industrially-Influenced Great Lakes Coastal Wetland(2020-12) White, AmberThe production and export of methylmercury (MeHg) is a critical first step to accumulation of mercury (Hg) in the lower food web and subsequent magnification in game fish. The purpose of this thesis was to identify areas of MeHg production and export in a freshwater estuary with a history of industrial influence by using ecological boundary delineations. Sediment, porewater and surface water was collected over two seasons from eleven sites encompassing four high-carbon sheltered embayments, two intermediate-carbon clay-influenced bays, and five low-carbon industrially influenced bays in the St. Louis River Estuary (Duluth, Minnesota). Ecologically delineated areas contained characteristically different quantities of Hg and MeHg and appear to be a useful framework for identifying locations likely to experience a net production of MeHg. The results provide a basis for understanding how MeHg can move through freshwater aquatic environments with complex hydrogeochemistry and could form the basis for effective resource management decisions.Item Impact Of Increased Temperature And Atmospheric Carbon Dioxide On Mercury And Sulfur Speciation In Peatland Soils(2018-08) Krupp, Anna LuciaEnvironmental mercury (Hg) pollution exists as a global public health issue without any localized borders. Volatile Hg emissions travel freely throughout the atmosphere, allowing anthropogenic point-source industrial emissions to have truly global impact. Recent research demonstrates that climate change may further impact the extent of environmental mercury pollution through increased production of monomethylmercury, more commonly known as methylmercury (MeHg), by various microorganisms within the soil, including sulfate-reducing bacteria, iron-reducing bacteria and methanogens. Continued research on the subject is warranted to fully understand the impacts of climate change on the environmental biogeochemical cycling of Hg and MeHg on various natural systems. Increasing global temperatures and levels of atmospheric CO2 could significantly increase the net conversion of Hg to MeHg by sulfate-reducing and iron-reducing bacteria in systems particularily vulnerable to climate change such as ombrotrophic peatbogs, leading to an increased size in the net MeHg pool overall. The Supplementary Files attached to this thesis document include the following files: raw data (SPRUCE_2012_2014_2015_2016_Peat_Final_Data.xlsx), untransformed multiple linear regression values (Regression_Non_Transformed.xlsx), log transformed multiple linear regression values (Regression_Log_Transformed.xlsx), maximum value calculations (Max_Calculations.xlsx), and fitted XANES data for 2012 (SPRUCE-2012-fit7-tidy.xlsx), 2015 (SPRUCE-2015-fit4-tidy.xlsx), and 2016 (SPRUCE-2016-fit4-tidy.xlsx).Item Mercury accumulation in raptors(2016-01) Keyel, EdwardMercury (Hg) is a toxic heavy metal that when methylated to form methylmercury (MeHg), bioaccumulates in exposed organisms and biomagnifies through food webs. Most studies examining Hg concentrations in birds of prey have focused on species associated with aquatic systems such as Bald Eagle (Haliaeetus leucocephalus). My goal was to assess Hg concentrations in multiple species of migrating raptors in the upper Midwestern US. From 2009-2012, 966 raptors of 11 species were captured at Hawk Ridge, Duluth, MN, USA. Breast feathers were sampled and analyzed for total Hg concentrations, which is a good analog for methlymercury. Mean Hg concentrations ranged from 0.11 – 3.46 ppm. Carbon and nitrogen stable isotope values were analyzed for Sharp-shinned Hawk (Accipiter striatus) and Merlin (Falco columbarius) because they had the highest mean Hg concentrations with 3.46 and 2.15 ppm respectively. Stable isotope analysis suggested that both species consumed terrestrial prey and that total Hg concentration increased with trophic level. Further analysis of Sharp-shinned Hawk and Merlin feather samples show Hg increases with age. The Hg concentrations observed in Sharp-shinned Hawks, Merlins, and Northern Goshawks (Accipiter gentilis) represent a concern when compared with concentrations found in the American Kestrel (Falco sparverius); one of the few raptors with enough experimental data for comparison.Item Mercury in Streams at Grand Portage National Monument: Evidence of Ecosystem Sensitivity and Ecological Risk(2012) Wiener, James GThis is a 4-page pdf, which apparently has not been published although the paper reviewers are named. The origin of the paper is unclear, and it should be regarded as “gray” literature. Key points are extracted and reproduced below. “In 2008, the University of Wisconsin-La Crosse began quantifying mercury in aquatic food webs in six national park units in the western Great Lakes region, including Grand Portage National Monument (GRPO). Principal objectives are (1) to identify parks and water bodies where concentrations of methylmercury are high enough to adversely affect fish and wildlife, and (2) to assess spatiotemporal patterns in methylmercury contamination of aquatic food webs. Methylmercury is a highly toxic compound that readily bioaccumulates in exposed organisms and can biomagnify to harmful concentrations in organisms in upper trophic levels of aquatic food webs. Study sites at GRPO include Snow Creek (beaver pond in upper reaches and lower reaches), Poplar Creek (south branch), and Grand Portage Creek (lower reach). Analytical results reveal elevated concentrations of both total mercury and methylmercury in these stream systems... Concentrations of total mercury and methylmercury in streamwater from GRPO are substantially higher than concentrations typically found in lakes and streams in the western Great Lakes region. “Bioaccumulation and ecological risk. In 2010, prey fish were sampled from three streams in the park and analyzed whole for total mercury, which accumulates in fish as methylmercury. Mean concentrations were highest, exceeding 100 ng/g wet weight (nanograms per gram, equivalent to parts per billion) in blacknose dace (Rhinichthys atratulus) and longnose dace (Rhinichthys cataractae) from Poplar Creek. These mean concentrations in dace substantially exceed the estimated dietary threshold (40 ng/g wet weight in prey fish) associated with reproductive effects of mercury on piscivorous fish that feed on prey fish (Depew et al. in press). Mean concentrations of mercury in most of the other prey fishes analyzed also exceeded the 40 ng/g threshold for reproductive effects on piscivorous fish; these included creek chub (43 ng/g) and central mudminnow (56 ng/g) from Poplar Creek, fathead minnow (58 ng/g) and central mudminnow (55 ng/g) from Snow Creek, and longnose dace from Grand Portage Creek (67 ng/g). The maximal concentrations in individual fish were 242 ng/g in blacknose dace and 211 ng/g in longnose dace. These maximal values exceed dietary thresholds associated with adverse effects of methylmercury on the health and reproduction of fish-eating birds. “The high concentrations of methylmercury in larval dragonflies may indicate significant risks for insectivorous songbirds that forage and nest near streams at GRPO. Studies in eastern North America have documented unexpectedly high concentrations of mercury (present as methylmercury) in certain terrestrial invertivores, including passerine songbirds. Most songbirds with elevated concentrations of mercury are linked trophically to mercury-methylating environments—such as wetlands, streams, or lakes—and feed on spiders or emergent insects with aquatic larval stages. Methylmercury in the diet of reproducing female birds is transferred rapidly to the developing egg, and the embryo is the most sensitive life stage. Methylmercury exposure and its potential effects on reproductive success of invertivorous songbirds at GRPO has not been assessed but merits critical evaluation.”Item Mercury Methylation in Denitrifying Bioreactors: An Investigation in Pollution Swapping(2015-08) Natarajan, MichelleWoodchip and corn cob filled bioreactors have been shown repeatedly to be effective at reducing nitrate pollution from agricultural fields by supporting denitrifying bacteria. Little attention has been paid, however, to other microorganisms that may also proliferate in these environments. Of particular concern are sulfate reducing bacteria and other organisms known to convert mercury to highly toxic methylmercury, since supporting such organisms could lead to increased levels of methylmercury in downstream rivers and lakes. To investigate this concern, we conducted two studies. We measured total and methylmercury concentrations and related parameters in upflow column bioreactors filled with either woodchips or corn cobs. The temperature of the water pumped into the column bioreactors was in the range of 1.8�C to 18.6�C to simulate cooler autumn and winter weather. There was no significant mercury methylation detected at these temperatures. The concentration of methylmercury flowing out of the column bioreactors filled with corn cobs showed greater variability than that of woodchip filled bioreactors. The second study was set up to pump water with low concentrations of nitrate into four edge-of-field woodchip bioreactors to produce a residence time of 24 hours or more. We measured total and methylmercury concentrations along with other indicators of water chemistry and biological activity. While the conditions monitored in the bioreactors were consistent with documented conditions that support mercury methylating bacteria, we did not find evidence of methylmercury being generated within the bioreactors. These studies indicate that the production of methylmercury is not likely in Minnesota edge-of-field woodchip bioreactors or in woodchip or corn cob bioreactors where water temperatures are below 18.6�C and nitrates are not completely reduced.Item Mercury Release from Taconite During Heating(University of Minnesota Duluth, 2005) Benner, Blair RThe taconite industry is under pressure to reduce the emissions of mercury from their induration process. Previous studies have indicated that greater than 90 percent of the mercury in the green balls being fed to the induration process is vaporized during the induration. The Minnesota DNR is in the process of conducting a bench-scale study to determine the rate of mercury release as a function of temperature during the heating of taconite. This program is a supplement to that work. The objectives of this program were to determine the role of oxidation in the release of mercury at various temperatures and to provide samples of heated material for Mossbauer spectroscopic analysis.Item Microbial Interactions: From Microbes to Metals(2016-01) Kane, AunicaMicrobial communities are the major drivers of biochemical cycling and nutrient flux on the planet, yet despite their importance, the factors that influence and shape behavior and function of microbial ecosystems remain largely undefined. The knowledge gap existing for microbial communities stems partly from a focus of microbiologists on monoculture but also because studies of multispecies systems are impeded by their complexity and dynamic nature. Synthetic ecology, the engineering of rationally designed communities in well-defined environments, provides an innovative and robust approach to reduce the complexity inherent in natural systems and mimic microbial interaction in a controlled framework. Synthetic ecology was used to engineer a co-culture using two previously non-interacting bacteria, Shewanella oneidensis and Geobacter sulfurreducens, both organisms important for multiple applications in biotechnology. The S. oneidensis and G. sulfurreducens co-culture provided a model laboratory co-culture to study microbial interactions and revealed that genetic mutations in metabolic pathways can provide the foundation to initiate cooperation and syntrophic relationships in multispecies ecosystems. Syntrophy between S. oneidensis and G. sulfurreducens was studied further using three-electrode bioreactors. Both S. oneidensis and G. sulfurreducens are capable of respiring insoluble terminal electron acceptors, a process termed extracellular respiration. During extracellular respiration, electrons produced during oxidative metabolism are transferred across both membranes to the outer surface of the bacterial cell where they reduce terminal electron acceptors such as metal oxides. Extracellular respiration can be monitored in real time as current produced in bioreactors with electrodes serving as a proxy for metal oxides. The ability of both S. oneidensis and G. sulfurreducens to transfer electrons to their outer surface enabled the study of a process central to many syntrophic communities known as interspecies electron transfer – the transfer of reducing equivalents between organisms. Mutants in various electron transfer pathways revealed that interspecies electron transfer in an obligate S. oneidensis/G. sulfurreducens co-culture was mediated by soluble redox-active flavins secreted by Shewanella serving as electron shuttles between species. The second half of this thesis focuses on S. oneidensis metabolism and interactions of microbes with metals. Microbial transfer of electrons to metals has a large impact on biogeochemical cycles and can also be harnessed for biotechnology applications in bioenergy and bioremediation. In order to effectively engineer S. oneidensis for these applications, it is imperative to understand how Shewanella gains energy from the oxidation of electron donors and the efficiency of electron transfer to metals and electrodes. Work in Chapter 4 revealed formate oxidation to be a central strategy under anaerobic conditions for energy conservation through the generation of proton motive force in S. oneidensis. Work in Chapter 5 quantified the effect of hydrogen metabolism on electron transfer reactions in Shewanella three-electrode bioreactors. Deletion of the hydrogenase large subunits, hyaB and hydA, in Shewanella resulted in higher current density and coulombic efficiency in single-chamber three-electrode bioreactors by diverting electron flux to the anode instead of to hydrogen production. The final chapter of this thesis focused on harnessing microbial transformation of metals for bioremediation purposes. An engineered Escherichia coli strain containing a mercury resistance plasmid was constructed to facilitate the remediation of organic and ionic forms of mercury pollution. The engineered strain was then encapsulated using silica sol gel technology generating a bio-filtration material for use in bioremediation platforms. Work in this thesis highlights the importance of microbial interactions, both with other organisms and with metals in the environment. Comprehensive knowledge on microbial interactions is important not only for a better understanding of ecosystem function but can also be harnessed for biotechnology applications. Microbial interactions and transformation of metals shape the world around us and have also facilitated use and further engineering of microorganisms for bioenergy and bioremediation technologies.Item A New Insight Into The Geochemistry Of Sulfur In Low Sulfate Environments(2018-08) Fakhraee, MojtabaAs an essential element for life, sulfur plays an important role in the biosphere, hydrosphere, atmosphere and lithosphere. Studies of sulfur cycling have been traditionally concentrated on modern marine environments with 28mM of sulfate, yet its importance in low sulfate environments such as large freshwater systems as well as the oceans of the geologic past (>0.5 billion years ago) cannot be neglected. This thesis, through modeling and theoretical approach, aims to provide a new insight into several aspects of sulfur cycling in low sulfate environments. For example, it is widely assumed that water-column sulfate is the main sulfur source to fuel microbial sulfate reaction in sediments. While this assumption may be justified in high-sulfate environments such as modern seawater, I show that in low-sulfate environments mineralization of organic sulfur compounds can be an important source of sulfate and sedimentary sulfide. The results in this thesis indicate that in low sulfate environments (<500 µM) the in-sediment production of sulfate can support a substantial portion (>50%) of sulfate reduction. Extrapolating the results to Archean oceans with tens of µM of sulfate, modeling results reveal that sulfite generated by mineralization of organic sulfur could fuel microbial S reduction in the absence of ambient sulfate, and hydrogen sulfide generated by mineralization of reduced organic S compounds could provide a pathway to pyrite that bypassed the microbial reduction of sulfate or sulfite. Reproducing isotopic records in the sedimentary sulfides from the rock record, modeling results show that in the low sulfate (<10 µM) environment of the Archean oceans (2.5-4 billion years ago), oxygen could have accumulated to up to 25 µM, while being consistent with the sulfur isotopic composition in Neoarchean rocks. A mass balance model coupled to a sediment diagenesis model suggests that seawater sulfate concentrations during the Proterozoic Eon (0.5-2.4 billion years ago) remained below 1.5% of modern values (<500 µM), and possibly as low as 100 µM. Using exploratory modeling of sulfur cycling, I also constrain the geochemical factors that control the fluxes of methylmercury from modern freshwater sediments. Modeling results identify oxygen, sulfate, and organic matter as leading geochemical parameters. They also suggest a critical level of oxygen at the sediment water interface, below which methylation rate dominates demethylation rate, resulting in an efflux of methylmercury into overlying water.Item Sorbent Nanotechnologies for Water Cleaning(2017-07) Ahmed, SnoberDespite decades of regulatory efforts to mitigate water pollution, many chemicals, particularly heavy metals, still present risks to human health. In addition to direct exposure, certain metals such as mercury threaten public health due to its persistence, bioaccumulation and bioamplification throughout the food chain. A number of U.S. Federal and State regulations have been established to reduce the levels of mercury in water. Activated carbon (AC) has been widely explored for the removal of mercury. However, AC suffers from many limitations inherent to its chemical properties, and it becomes increasingly challenging to meet current and future regulations by simply modifying AC to enhance its performance. Recently, the performance of nanosorbents have been studied in order to removal pollutants. Nanosorbents utilize the ultra-high reactive surface of nanoparticles for rapid, effective and even permanent sequestration of heavy metals from water and air, thus showed promising results as compared to AC. The goal of this thesis research is to develop nanomaterial-based sorbents for the removal of mercury from water. It describes the development of a new solid-support assisted growth of selenium nanoparticles, their use for water remediation, and the development of a new nanoselenium-based sorbent sponge for fast and efficient mercury removal. The nanoselenium sorbent not only shows irreversible interaction with mercury but also exhibits remarkable properties by overcoming the limitations of AC. The nanoselenium sponge was shown to remove mercury to undetectable levels within one minute. This new sponge technology would have an impact on inspiring new stringent regulations and lowering costs to help industries meet regulatory requirements, which will ultimately help improve air and water quality, aquatic life and public health.Item Sulfate and Mercury Chemistry of the St. Louis River in Northeastern Minnesota: A Report to the Minerals Coordinating Committee(2009) Berndt, Michael; Bavin, TravisThis report presents technical data and information on water quality sampling from the St. Louis River related to sulfate and mercury contamination from mining that may affect human health. However the report contains raw data with little interpretation, and gives little guidance as to application of the findings to decision-making. The abstract and key findings are reproduced below. The St. Louis River and its major tributaries were sampled upstream from Cloquet during periods of high, medium, and low flow between September 2007 and October 2008. Special emphasis was placed on measuring sulfate (SO4) and mercury (Hg) distributions as well as other chemical parameters that might help to determine whether SO4 releases from the Iron Range have an impact on Hg speciation in the St. Louis River. These included, but were not limited to, dissolved organic carbon (DOC), dissolved iron (Fe), and the isotopic ratios for sulfur and oxygen atoms in dissolved SO4 (δ34SSO4 and δ18OSO4). Dissolved and particulate fractions of methyl mercury (MeHg), total mercury (THg), and bioavailable mercury (AHg) were additionally determined over a range of hydrologic conditions to identify primary source regions and transport mechanisms for Hg species. Results confirm that the majority of SO4 is derived from the iron mining district, and that SO4 added in the upstream portion of the St. Louis River is generally diluted downstream by waters from larger watersheds containing high percentages of wetlands. SO4, magnesium (Mg), calcium (Ca), sodium (Na), and chloride (Cl) concentrations all increase in the river, especially in the mining region, during periods of low-flow when groundwater inputs dominate chemistry of dissolved components. Variations in the relative concentrations of major elements and inδ34SSO4 and δ18OSO4 among the tributaries provide important clues to specific SO4 sources for each of the individual watersheds under varying flow conditions. Chemical data indicate that most SO4 from the mining region is derived from oxidation of small amounts of iron sulfide minerals present in stock piles, tailings, and pit walls containing Mg-rich carbonate minerals that are common in the Biwabik Iron Formation. Comparison with stream chemistry from 1955 to 1961 indicates SO4 sources were commonly present in the mining region before taconite mining became widespread in the region. Other chemical parameters in these data, particularly Ca and Mg, indicate the primary source for this SO4 was different from today. In contrast to SO4, Hg appears to be derived predominantly from wetlands, and is highest during periods of increased flow in the rivers. THg is well correlated to DOC concentration under most conditions, but quite variable during precipitation events when dissolved AHg and particulate SHg become more abundant in the rivers. MeHg concentrations in the St Louis River and its tributaries are also strongly correlated to DOC. Four sources of DOC are preliminarily inferred to be present in the river depending on the season and watershed characteristics, and it is believed that the relative amounts of DOC from each source may control the MeHg concentrations present in the river. These include: (1) DOC released from surface wetland areas containing low Fe (approximately 0.2 ng/mg Hg and 0.02 ng/mg MeHg in the DOC), (2) DOC containing almost no MeHg that is either produced in-stream or present in small amounts in natural groundwater, (3) DOC released from deep wetland areas following a major summer rain event containing very high MeHg and high Fe, and (4) DOC containing almost no MeHg in waters containing elevated dissolved Fe that seep slowly from deep within wetland areas under dry conditions. MeHg systematics appear to be very similar to those reported in two well-studied low-SO4 tributaries of the Rum River in east-central Minnesota. Additional sampling is planned to verify the above model and to more fully characterize mercury speciation during the warm summer months, particularly during periods when high Fe concentrations are present in the streams.