Browsing by Subject "mercury"
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Item Comparative Neurotoxicity of Methylmercury and Mercuric Chloride In Vivo and In Vitro(2010-10-12) Thuett, Kerry A.It is impossible to remove methylmercury (MeHg) from biological systems because MeHg is found throughout our environment in many fresh and salt water fish. The consumption of fish is important to human nutrition and health. The mechanism of MeHg neurotoxicity must be understood to minimize adverse exposure consequences. The dissertation objective was to: 1) compare mechanisms of MeHg neurotoxicity between animals exposed as adults and those exposed during gestation, and 2) develop an in vitro test model of in vivo MeHg exposure. Total mercury (Hg) levels in tissue / cells were determined by combustion / trapping / atomic absorption. Cell death was determined by Fluoro-Jade histochemical staining and activated caspase 3 immunohistochemistry for in vivo studies, and Trypan blue exclusion, lactate dehydrogenase activity, and cytotoxicity assays for in vitro studies. Mitochondrial membrane potential (MMP), intracellular calcium ion concentration ([Ca2+]i), and production of reactive oxygen species (ROS) were determined using fluorescence microscopy or microplate reader assays. Young adult C57Bl/6 mice were exposed to a total dose of 0, 1.0, or 5.0 mg/kg body weight MeHg divided over postnatal days (P)35 to 39. Pregnant female mice were exposed to a total does of 0, 0.1, or 1.0 mg/kg body weight MeHg divided over gestational days (G)8 to 18. SY5Y cells were exposed to 0, 0.01, 0.1, or 1.0 ?M MeHg or HgCl2 for 24, 48, or 72 hours. Total Hg in brains of young adult mice, mouse pups, and SY5Y cells accumulated in a dose-dependent manner. Cell death increased in SY5Y cells exposed to the highest concentrations of MeHg and HgCl2 used in this study. Cell death increased in the molecular and granule cerebellar cell layers of young adult mice exposed to the highest doses of MeHg used in this study. P0 mouse pups showed no increase in cell death within the cerebellum following MeHg exposure. Cerebella of mice at P10 exhibited decreased dying cells only in the external germinal layer. Low concentrations of MeHg affected MMP in both in vivo and in vitro studies, but did not result in decreased MMP typically associated with higher MeHg concentrations. [Ca2+]i was increased throughout the in vivo experiments in an age- , sexand brain region-dependent manner. Generation of ROS was decreased in both in vivo and in vitro studies with both the MeHg and HgCl2 (in vitro) treatments. In summary, low and moderate MeHg exposure, both in vivo and in vitro, altered mitochondrial function, Ca2+ homeostasis, and ROS differently than what is reported in the literature for higher MeHg exposure concentrations. SY5Y cells were sensitive to low-levels of MeHg and HgCl2 and responded similarly to cells in the whole animal studies, thus making SY5Y cells realistic candidates for mechanistic MeHg studies. Cell culture and whole animal neuronal functional studies at chronic low-level MeHg exposure are limited. These data suggest that low-levels of MeHg may affect neuronal function. Therefore, further chronic low-level MeHg neuronal functional studies are warranted.Item Heavy atom induced phosphorescence of organic materials using mono- and trifunctional organomercury derivatives(2009-05-15) Burress, Charlotte NicoleThis dissertation focuses on the phosphorescence of organic chromophores using perfluoro-ortho-phenylene mercury (1) and bis(pentafluorophenyl)mercury (2) as external heavy atom effect inducers. To ascertain the suitability of these luminescent adducts for OLED applications, several research objectives have been investigated. To further shorten the triplet lifetimes of adducts involving 1, a strategy was developed which combines both internal and external heavy atom effects. Specifically, complexes involving 1 and N-methylcarbazole, N-methylindole and the 1- halonaphthalenes were investigated. The existence and stability of the complexes could be confirmed in solution by fluorescence spectroscopy. In the solid state, these adducts form supramolecular binary stacks where the molecules of 1 alternate with the aromatic substrate. As a result of the mercury external heavy atom effect, all of these adducts display intense room temperature phosphorescence of the free arene. With the Nheterocycles, the triplet lifetimes were drastically reduced to below 100 mu-s. To appreciate the origin of the unusual heavy atom effects observed in arene adducts with 1, 2 was studied as a monofunctional analog to 1. By utilizing fluorescence spectroscopy, naphthalene, biphenyl, and fluorene complexes of 1 and 2 have been detected in solution. The solid state structure of the adducts with 2 reveal supramolecular binary stacks. Comparison of the photophysical results supports the occurrence of cooperative effects between the Lewis acidic mercury centers of 1, which make it a more efficient external heavy-atom effect inducer. Polymeric materials which are amenable to deposition in thin layers were investigated as substrates for 1 and 2. Both poly(vinyl-2-naphthalene) and poly(vinylcarbazole) interact with 1 and 2 in solution as evidenced by fluorescence spectroscopy. With the solid blend 1?PVK, a small doping percentage of 1 results in white emission, while larger percentages of 1 yield bright orange emission. This dissertation presents the first structurally characterized ternary complex with 1, carbazole, and coordinating solvents THF and triethylamine. IR spectroscopy and short N???O and N???N distances in the solid state indicates that the acidic N-H moiety of carbazole interacts with the solvent by hydrogen bonding. In the extended structure, molecules of 1 and the hydrogen bonded complex alternate to form supramolecules.Item Mercury speciation in Galveston Bay, Texas: the importance of complexation by natural organic ligands(Texas A&M University, 2005-02-17) Han, SeungheeThe major goal of this research is the development of a competitive ligand equilibration-solvent solvent extraction (CLE-SSE) method to determine organically complexed mercury species in estuarine water. The method was applied to estuarine surface waters of Galveston Bay and the water column of Offatts Bayou. Thermodynamic equilibrium modeling estimated organically complexed mercury species in estuarine water using the conditional stability constants of mercury-organic complexes and the concentrations of organic ligands determined by CLE-SSE. Two competing ligands, chloride and thiosalicylic acid (TSA), were used for CLE-SSE. Chloride ion competition determined conditional stability constants for 1 : 1 mercury-ligand complexes ranging from ~1023 to ~1024 with concentrations of organic ligands at low nM levels. TSA competition determined stronger mercury-binding ligands by manipulating the TSA concentration such that a higher binding strength was achieved than that for the mercury-chloride complex. TSA competition determined conditional stability constants for 1 : 1 mercury-ligand complexes ranging from ~1027 to ~1029, with ligand concentrations ranging from 10 to 100 pM. Mercury-organic binding strengths in these ranges are consistent with bidentate mercury complexation by low molecular weight organic thiols. A linear relationship was observed between log stability constants for the mercury-ligand complex and log ligand concentrations, supporting the hypothesis that there is a continuum of mercury binding site strengths associated with dissolved organic matter. In Galveston Bay, organically complexed mercury accounted for > 95 % of the total dissolved mercury in surface water. Organic complexation of mercury coupled with mercury dissolution from particulate phases controls the filter-passing mercury distribution in surface waters of Galveston Bay. The estuarine distributional features of mercury-complexing organic ligands were similar to those of glutathione, supporting mercury complexation by a thiol binding group. In Offatts Bayou, a seasonally anoxic bayou on Galveston Bay, thermodynamic equilibrium modeling suggests that the speciation of dissolved mercury in anoxic systems is dominated by sulfide complexation rather than organic complexation.Item Modeling of the reburn process with the use of feedlot biomass as a reburn fuel(2009-05-15) Colmegna, GiacomoCoal fired power plants will face many challenges in the near future as new regulations, such as the Clear Sky Act, are being implemented. These regulations impose much stricter limits on NOx emissions and plan to impose limits on mercury emissions from coal fired boilers. At this time no technologies are currently being implemented for control of Hg and this explains the strong interest in this area by the Department of Energy (DOE). Reburn technology is a very promising technology to reduce NOx emissions. Previous experimental research at TAMU reported that Feedlot Biomass (FB) can be a very effective reburn fuel, for reduction of NOx up to 90%-95%; however, little work has been done to model such a process with Feedlot Biomass as reburn fuel. The present work addresses the development of a reburn model to predict NOx and Hg emissions. The model accounts for finite rate of heating of solid fuel particles, mixing with NOx laden hot gases, size distribution, finite gas phase and heterogeneous chemistry, and oxidation and reduction reactions for NOx and Hg. To reduce the computational effort all the reactions, except those involved in mercury oxidation, are modeled using global reactions. Once the model was validated by comparison with experimental findings, extensive parametric studies were performed to evaluate the parameters controlling NOx reduction. From DOE research programs some experimental data regarding the capture of mercury from power plant is available, but currently no experimental data are available for Hg emission with reburn process. This model has shown a very large mercury reduction using biomass as a reburn fuel. The model recommends the following correlations for optimum reduction of NOx: Equivalence Ratio should be above 1.05; mixing time should be below 100ms (especially for biomass); pure air can be used as the carrier gas; the thermal power fraction of the reburner should be between 15% and 25%; residence time should be at least 0.5s and the Surface Mean Diameter (SMD) of the size distribution should be as small as possible, at least below 100 ?m.