Browsing by Subject "Methylmercury"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    The Effect Of Climate Change On Mercury In Boreal Peatlands
    (2023-09) Pierce, Caroline
    Mercury 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.
  • Thumbnail Image
    Item
    The effect of high sulfate loading on methylmercury production, partitioning, and transport in mining-imapcted freshwater sediments and lakes in northeastern Minnesota
    (2015-02) Bailey, Logan Timothy
    Methylmercury (MeHg) is a highly toxic form of mercury with the ability to bioaccumulate in food webs. The bioaccumulation of MeHg leads to elevated MeHg levels in fish tissue and poses a threat to public health. Thus MeHg concentrations in surface waters - which may be a result of water column MeHg production, or sediment MeHg production and subsequent flux from sediment porewater - are of particular concern. The production of MeHg from inorganic mercury (iHg) is primarily a result of sulfate-reducing bacteria (SRB) activity in anoxic aquatic environments.Ongoing and historic mining activity on the Mesabi Iron Range (Minnesota, USA) has led to elevated sulfate levels in the downstream waters of the St. Louis River watershed. In an effort to understand the effect of mining-related sulfur-loading on the production and partitioning of MeHg, sediment samples were collected and analyzed from sulfur impacted and non sulfur-impacted lakes and wetlands within the watershed. Additionally, the water column and inlet and outlet streams of a mesotrophic lake (Lake McQuade) were sampled intensively during summer stratified conditions in order to identify the sources and sinks of MeHg to the lake system and determine the potential for MeHg export downstream.Results suggest that dissolved sulfide plays a large role in governing MeHg dynamics in sulfate-impacted freshwater sediment. Consistent with previous research, net MeHg production appeared to be inhibited in sediments with dissolved sulfide >60 uM. However, these high concentrations of dissolved sulfide were accompanied by increased partitioning of MeHg into the porewater phase, potentially increasing the fraction of MeHg available to be transported into surface waters.Sediment at sulfate-impacted sites was generally characterized by high dissolved sulfide and a low potential for long-term net MeHg production. However, the accumulation of dissolved sulfide in sediment porewaters can be limited by the availability of free labile iron (Fe2+) and consequent iron-sulfide precipitation reactions. In the results presented here, high sulfur-loading at two sites appeared to have consumed the available free labile iron and created conditions which allowed for the accumulation of dissolved sulfide and inhibition of MeHg production in the sediment. However, relatively high sulfur-loading(>100 mg/L) to a third site where iron remains in excess of sulfur in sediment may have led to robust net MeHg production, in absence of inhibitory dissolved sulfide concentrations. Accumulation of MeHg in the hypolimnion of Lake McQuade occurred during summer 2012 during a time when bottom water sulfate was being consumed. Though some uncertainty remains as to the ultimate source of the MeHg, estimates of MeHg inputs and outputs to the hypolimnion suggest that water column production was a primary source of MeHg to the hypolimnion during the stratified summer months. Following the wet spring months when inputs were dominated by upstream flows, the flux of MeHg across the limnetic surface was estimated to be the primary source of MeHg to the epilimnion during the stratified summer months. However, most of MeHg input to the epilimnion was apparently degraded prior to being exported to the outlet stream. Thus, despite mid-summer accumulation of MeHg in the hypolimnion, the combination of stratification and substantial degradation in the epilimnion acted to limit export of MeHg out of Lake McQuade.As a whole, Lake McQuade acted as small net source of MeHg to the surrounding water system during the summer months of 2012. Evidence points to a brief rise in MeHg export immediately following lake turnover in Mid-August due to the release of hypolimnetic MeHg to surface waters during lake mixing.
  • Thumbnail Image
    Item
    Impact Of Increased Temperature And Atmospheric Carbon Dioxide On Mercury And Sulfur Speciation In Peatland Soils
    (2018-08) Krupp, Anna Lucia
    Environmental 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).
  • Thumbnail Image
    Item
    Mercury in Streams at Grand Portage National Monument: Evidence of Ecosystem Sensitivity and Ecological Risk
    (2012) Wiener, James G
    This 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.”
  • Thumbnail Image
    Item
    Minimizing Methylmercury Exposure in the Hmong Community from Sport-Caught Fish Consumption in Minnesota
    (Humphrey Institute of Public Affairs, 2008-06) Endreson, Daniel
    Due to increasing levels of mercury emissions throughout the world, there is an increased threat to the human population from methylmercury, a biomethylated derivative of mercury. Methylmercury is a dangerous neurotoxin that can have adverse effects on the central nervous system and behavioral centers of the brain. Humans can become exposed to methylmercury through consumption of contaminated fish from polluted waters. Many states, including Minnesota, use fish consumption advisories to warn the public of methylmercury exposure, but these advisories may not always reach at-risk segments of the population. The Hmong community in the Twin Cities consumes a high quantity of sport-caught fish for a variety of reasons, including a desire to maintain cultural identity, recreation, or economic necessity, even though fish consumption advisories warn against such actions. Four alternatives were considered to provide better protection to the Hmong community from methylmercury exposure – (1) continue the use of fish consumption advisories as developed by the Minnesota Department of Health (MDH), (2) alter the current program by reallocating advisory education efforts from state agencies to local governmental units and organizations, (3) impose a ban on the consumption of all fish from methylmercury-impaired waters in the Minneapolis/St. Paul metropolitan area, and (4) establish more Asian-specific food shelves in the Twin Cities area to provide food alternatives to sport-caught fish. Each of these alternatives were evaluated using six criteria – safety effectiveness, program awareness, social and cultural acceptability, administrative operability, program cost, and health benefit. This report concludes that efforts taken by the MDH in educating Hmong anglers have the promise of being effective in reducing methylmercury exposure from fish consumption. However, based on theories of risk perception and communication, more needs to be done at both the state and local level to effectively target this specific subpopulation in Minnesota.