The production of methyl mercury, an acute neurotoxin which readily accumulates in the tissue of organisms, is a biologically mediated process facilitated by sulfate reducing bacteria in aquatic sediments. In-situ capping is a frequently considered risk management strategy for contaminated sediments. Since placement of an in-situ cap will induce anaerobic conditions that are known to be favorable for the growth of sulfate reducing bacteria, there is justifiable concern that capping could increase mercury methylation in underlying sediments. This research builds an understanding of the effects of in-situ capping on underlying biogeochemical processes and elucidates their importance in controlling methyl mercury production. Laboratory experiments and mathematical models were implemented to simulate mercury methylation in redox conditions likely to be induced by capping using sediment from different environments. Mathematical descriptions of processes known to be involved in methylation were incorporated into the model to quantify the effects of these processes. Observations in both well-mixed slurry conditions and intact sediment columns showed that methyl mercury concentrations are strongly dependent upon biogeochemical conditions. Results from experiments with sediment spanning a range of redox conditions and organic contents suggested that sulfate reduction rates, aqueous speciation, and solid phase partitioning are involved in limiting methylation depending on bulk geochemical characteristics. A model with a mechanistic basis that incorporates the effects of these processes provides a useful means of qualitatively and quantitatively considering their cumulative impact in limiting methyl mercury production. High methyl mercury concentrations observed in some lab experiments suggest that there is reason to be concerned about anoxic conditions induced by capping; however, not all anoxic conditions led to equivalent increases in methyl mercury. Experimental and modeling results suggest that in a high organic environment, in-situ capping may produce conditions which accelerate methylation in (formerly) surficial sediment while in a low organic environment, with an overall lower potential for methylation, capping can be expected to have a less dramatic effect. Over time, two processes will temper capinduced increases in methyl mercury. Increases will only last until sulfide builds up to inhibitory levels in underlying sediment or until organic carbon is depleted and overall bacterial activity slows. By providing a more fundamental understanding of the effects of capping on mercury methylation, the results of this research will aid in identifying situations and conditions in which cap-induced increases in methyl mercury have the potential to limit the effectiveness of the management strategy. / text

No description available.

In various industries, specialized filters with activated carbon are used for adsorbing mercury from air-flows. MRT has eight such Activated CarbonFilters (ACFs) in one of their devices. The main purpose of research is tostudy the flow in the ACF filter and suggest a mathematical model for the complete system through which an improved design can be found.Simulation of a single ACF illustrates how the current system’s air flow does not cover the whole filter leaving part of the carbon bed unused forthe adsorption. This is validated by experimental data. A theoretical studybased on a mathematical model is made and the improved air flow pattern of a re-designed ACF is presented. An additional improvement is that byswitching inlet and outlet the usable time of the filters is prolonged.

The various origins proposed for intercrater plains on Mercury and the Moon lead to divergent thermal, tectonic, and bombardment histories. Relative ages of geologic units and structures place tight constraints on their origin and on the planet's geologic history. Crater statistics, lunar geologic map analysis, and geologic mapping of a quarter of Mercury's surface based on plains units dated relative to crater degradation classes were used to determine relative ages. Such studies provided the basis for deducing the origin of intercrater plains and their role in terrestrial planet evolution. Mercury's extensive intercrater plains span a range of ages contemporaneous with the period of heavy bombardment. Most intercrater plains predate scarp formation and the formation of the hilly and lineated terrain. The age of the latter is identical to that of its probable progenitor, the Caloris basin impact. Post-Caloris plains--smoother in texture, less extensive, and confined to crater depressions--formed as cratering waned and scarp formation progressed. This research indicates that mercurian intercrater plains are volcanic deposits interbedded with ballistically emplaced ejecta and reworked by basin secondaries and smaller impacts. A greater proportion of ejecta may comprise lunar intercrater plains. Neither the lunar nor mercurian intercrater surface is primordial because each preserves pre-plains crateriforms. Ancient volcanism on Mercury is evidenced by widespread plains distribution, structurally controlled deposition, embayment of craters and basins, associated (but tentative) volcanic landforms, losses of small craters, and uncorrelated plains and crater coverage. The limited range of mercurian ejecta reduces the resurfacing potential relative to that of lunar craters. Crater densities are affected by intercrater plains emplacement, additions of secondaries, ancient basin impacts, and target physical properties. "One-plate" thermo-tectonic models best explain the geologic characteristics recognized in this study. Thermal expansion during core formation causes global extension and widespread volcanic extrusions; subsequent cooling and radial contraction form compressional scarps. Younger plains-forming materials issue from magma reservoirs in subsurface tensional zones tapped by impact fractures. The age and stress environment of these volcanic plains suggest a source greater than 40 km depth and a composition different from that of the intercrater plains.

To evaluate the niche of coastal fish populations in the Beaufort Sea, stable isotopes (SI) and fatty acids (FA) were used to characterize species-specific niches, niche overlaps and resource partitioning (nicheROVER) of the Shingle Point fish populations. Fishes were grouped into three isotopic groups: marine, coastal, and freshwater (Ward’s clustering analysis), and five dietary groupings (using FA), where benthic feeding strategies were prevalent (correspondence analysis). Niche metrics were used to evaluate if total mercury (THg) could contribute complementary trophic information (residual permutation procedure (RPP)). Three THg groups (high, intermediate, low) were identified (boxplot analysis). High THg was identified in high trophic and benthic feeders, high THg ranges were observed in species with large niche sizes, high trophic feeding, and freshwater influences (RPP). The bioavailability of freshwater introduced THg to marine biota was assessed, however further research needs to be performed. Combining dietary indicators SI, FA, and THg, allowed for the characterization of the diet and habitat use of coastal fish populations, better understanding of the niches of these species, and developed baseline information for future monitoring in an MPA, as climate change continues to effect the Beaufort coastal environment. / February 2017

In this dissertation I present experimental results obtained on the mercury optical clock project in the research group of Jason Jones at the University of Arizona. The project began in 2008 with the purpose of investigating the feasibility of neutral mercury as an optical clock species. The first series of investigations involved building the essential apparatus and scanning the doppler-broadened 6¹S₀ - 6³P₀ clock transition in ¹⁹⁹Hg. Here I present significant modifications to the cooling and trapping laser, improvements to the spectroscopy laser linewidth, and attempts to measure the 2-photon transition in ¹⁹⁹Hg. After previously demonstrating spectroscopy of the mercury clock transition using an optically-pumped semiconductor laser for the cooling and trapping source (OPSL), we replaced the OPSL with a a fiber-amplified ECLD system. We custom built a fiber amplifier to provide gain at 1015 nm, demonstrating the system can yield up to 5 W of signal power with excellent suppression of the ASE power. We find that the ASE is well suppressed by using a two-stage configuration and short sections of gain fiber. The linewidth of our original spectroscopy laser was over 10 kHz, which is unsuitable to resolve of sub-Doppler features. To enhance the performance of our spectroscopy system, we integrated faster feedback bandwidth using AOMs, and incorporated derivative gain into the system. This resulted in a feedback bandwidth for our spectroscopy laser of over 200 kHz. With this system, we demonstrate anactively stabilized linewidth of 525 Hz for our spectroscopy system. Using the upgraded cooling and spectroscopy laser systems, we demonstrate spectroscopy of the clock system and confirm temperature measurements derived from the transition linewidth. We also describe attempts to detect the recoil shift and 2-photon transition in neutral mercury.

The original purpose of this investigation was to attempt to apply the coulostatic method directly to a molten salt system. The inability to duplicate the reported capacity data for this system resulted in an investigation of the probable cause of this discrepancy between the data obtained by these different methods (14, 15).

Pelagic forage fishes play critical roles in productive marine food webs by providing a link between zooplankton and piscivores and transferring energy from feeding grounds to other ecosystems. The amount of energy moved to higher trophic levels or new systems is directly linked to the consumption rate of pelagic forage fishes. In the Gulf of Maine, Atlantic herring (Clupea harengus) is the dominant forage fish; the purpose of this study is to determine their specific consumption rate (g prey/g fish/day). Using fish collected in autumn 2012 and spring 2013, we applied a mercury mass-balance model to estimate individual and population consumption of Atlantic herring in the Gulf of Maine. Our results suggest that the specific consumption rate increases from age 1.5 until age 6 (years) and then asymptotes. These estimates were contradictory to much of what exists in the literature; for most fishes, specific consumption estimates decrease with age and overall are much lower than our estimates. We looked further into our results to explore the underlying cause of the increase in specific consumption rate. We combined the mercury mass-balance model with a Wisconsin (WI) bioenergetics model and ran several simulations adjusting the most sensitive factors in each--prey mercury in the former and activity in the latter. The results of our simulations showed that an increase in activity relative to age and mass can best explain the increase in the consumption rate of Adult herring. This suggests that an ontogenetic shift to migration in adult Atlantic herring results in increased energy demand with age, and ultimately increased consumption.

O objetivo deste trabalho foi realizar a avaliação dos riscos ocupacionais ao mercúrio utilizado em odontologia, aos quais os auxiliares em saúde bucal (ASB) da rede pública de saúde do município de Araguaína, Tocantins, estão expostos. O processo odontológico do sistema de saúde no município em questão foi estudado, de modo minucioso, a partir de um levantamento do número de restaurações de amálgama de prata executadas durante o período de janeiro de 2003 a dezembro de 2007 na base de dados DATASUS. Nesse estudo, foram avaliadas as condições de armazenamento dos resíduos de amálgama nos consultórios odontológicos públicos do município analisado. Foram estudadas diferentes soluções-barreira para armazenamento dos resíduos de amálgama no que diz respeito a sua eficácia no combate à emissão de vapores de mercúrio para o ambiente. A solução contendo amoníaco foi a que apresentou melhor tempo para estocagem dos resíduos (19 dias a 37 ºC), seguida pela solução contendo fixador fotográfico (12 dias) e solução de bicarbonato de sódio (7 dias). Com base nestas informações, caracterizou-se o perfil do ASB que atua nos consultórios públicos do município de Araguaína quanto à idade, ao sexo, ao grau de exposição ao mercúrio e aos procedimentos de biossegurança executados. O estudo possibilitou elaborar um banco de dados, com relação ao manuseio e ao descarte de resíduos de amálgama, com o intuito de subsidiar políticas públicas de saúde voltadas à modificação de situações de risco as quais os profissionais estão submetidos e/ou submetem seus pacientes. Foi realizado também um programa de monitoramento biológico, utilizando como marcador a presença de mercúrio em amostras de urina (HgU), em membros da equipe odontológica da rede municipal de saúde de Araguaína e em alunos da escola técnica de saúde, polo de Araguaína, atuantes como ASB em outros municípios da região norte (n=91). Como comparação, um grupo de não expostos ao mercúrio foi avaliado (n=43) e os valores de HgU determinados. A pesquisa permitiu concluir que, em relação aos valores de HgU, a equipe odontológica avaliada estava dentro dos limites propostos pela NR 7 (até 35 gHg.g-1CR). Com relação à contaminação por mercúrio, a média da concentração do HgU para o grupo expostos (5,61 μgHg.g-1CR) foi aproximadamente 8 vezes maior se comparada ao do grupo não expostos (0,65 μgHg.g-1CR), evidenciando a necessidade de um programa de treinamento de profissionais e de gerenciamento de resíduos, bem como de uma atuação mais efetiva na realização do monitoramento biológico periódico nos profissionais da equipe odontológica. / The aim of this work was to evaluate the occupational risks of exposure to mercury utilized in dentistry, to which dental auxiliaries from the public health system of the city of Araguaína, Tocantins, Brazil are exposed. The dentistry process from the city health system was rigorously studied based on an assessment, in the DATASUS database, of the number of amalgam restorations conducted in the period from January 2003 to December 2009. In this study, we evaluated the storage conditions of mercury residuals in the public dental offices in the studied municipality. Different barrier solutions for the storage of mercury residuals were studied regarding their efficacy in controlling the emission of mercury vapor in the environment. The solution containing ammonia presented the best time of storage of residuals (19 days at 37 °C), followed by the so lution containing photographic fixative (12 days) and the sodium bicarbonate solution (7 days). Based on these information, a profile of the dental auxiliaries actuating in the public dental offices of the city of Araguaína was characterized according to age, sex, level of exposure to mercury and conducted biosecurity procedures. The study allowed the elaboration of a database regarding handling and discard of amalgam residuals, with the purpose to assist public health policies to modify risk situations to which the professionals and/or their patients are exposed. A biological monitoring program was also carried out using as marker the presence of mercury in urine samples (HgU) from members of the dentistry team of the Araguaína public health system and from students from the Araguaína unit of the health care technical school who actuated as dental auxiliaries in other municipalities of the north region of the state (n=91). For comparison, a group of not exposed to mercury was evaluated (n=43), determining their HgU values. The research allowed to conclude that the HgU values from the dentistry team were within the limits set by Regulatory Norm nº 7 by the Brazilian Ministry of Labor (up to 35 gHg.g-1CR). Regarding mercury contamination, the average HgU concentration for the exposed group (5,61 μgHg.g-1CR) was approximately 8 times higher when compared to the values from the not exposed group (0,65 μgHg.g-1CR), making evident the need for a professional training and residuals management program, as well as for a more effective actuation in the realization of periodical biological monitoring in the professionals from the dentistry team.

Nos últimos anos, acentuou-se o interesse em materiais semicondutores com alto número atômico e alto gap de energia para aplicações na detecção de radiação ionizante à temperatura ambiente, usando o método direto de detecção. Este trabalho apresentara as características de dois materiais semicondutores na forma de filme para o iodeto de chumbo e de cristal milimétrico para o iodeto de mercúrio. Os filmes foram depositados a partir da evaporadora térmica construída no próprio departamento e caracterizados em função de três distâncias de deposição. O melhor filme obtido foi produzido a 5 cm de distância da fonte, apresentando valores de gap de energia de 2,39 eV e energia de ativação de 1,1 eV. Com o aumento dessa distância as propriedades estruturais, ópticas e elétricas se deterioram, inclusive com variação da composição do material. Os cristais de iodeto de mercúrio foram dissolvidos no solvente orgânico N-N Dimetilformamida e crescidos utilizando a técnica de deposição de solvente. Diferentes taxas de crescimento foram usadas para o crescimento dos cristais. Os melhores resultados foram obtidos para crescimento na estufa a 80ºC, produzindo filmes com gap de energia de 2,2 eV e resistividade da ordem de 108 ?.cm, indicando dopagem não intencional ou excesso de defeitos. A composição obtida é de HgI3, e a razão da fotocorrente pela corrente de escuro quando na faixa de raios-X mamográficos é da ordem de 25. Com as otimizações indicadas no texto e na conclusão do trabalho esses materiais seriam fortes candidatos para aplicações comerciais em imagens médicas para energias na faixa mamográfica. / In the last years there has been a growing interest in semiconductor materials with high atomic number and optical band gap for applications as ionizing radiation detectors at room temperature, using the direct method of detection. Some materials such as lead iodide (PbI2) and mercury iodide (HgI2) have an optical band gap above 2,0 eV, operate at room temperature with low noise and low leakage current, present a high carrier mobility and high stopping power for ionizing radiation. Alternative methods are investigated by several researchers for the fabrication of these materials on top of large areas, with low fabrication time and costs as desirable for applications in medical imaging. In this sense, we present two methods for the development of the detectors. Thermal evaporation, with the development of the deposition system and chamber, is used for the fabrication of lead iodide thin films. The properties of the films were investigated as a function of deposition height. On the other hand, isothermal evaporation was used for the fabrication of mercury iodide milimetric crystals, for the first time using the organic solvent N.N- dimetilformamide (DMF). The properties of the crystals are investigated as a function of concentration and growth temperature. The structural, morphological and compositional properties of the films and crystals were investigated. The optical and electrical properties were also investigated for both films and crystals. The activation energy for electric transport and the test of the materials as sensors (using X-rays in the mammographic region) were studied. This work presents the main results for both materials: films of lead iodide and milimetric crystals of mercury iodide. The crystalline planes of the films have a preferential orientation along the (110) direction, and a morphology of vertical leaves, not similar to other reported results. The obtained composition is PbI2,5. The combination of the morphology and the configuration of co-planar contacts for charge collection reduce the sensitivity to X-rays exposure. A current density ratio (illuminated to dark) of the order of 1.53 was obtained. The best film was deposited at a distance of 5 cm to the source, and it has an optical gap of 2,39 eV and activation energy of 1,1 eV. With increasing deposition distance a degradation of the structural, optical and electrical properties was observed, even with the variation of the composition of the films. For mercury iodide, for any growth rate the shape of the crystals is always cubic. The morphology of the surface depends on the evaporation rate (it can be smooth or present macroscopic holes). The best results were obtained for a growth at 80o C, what leads to a crystal with optical gap of 2.2 eV and electrical resistivity of the order of 108 Ohmcm, what suggests non-intentional doping or excess of defects. The obtained composition was HgI3, and the current ratio (illuminated by mammographic X-rays to dark) was about 25. According to the discussions in the text and in the conclusions, the suggested optimizations could lead to the development of materials that might be useful for technological applications in medical imaging for the mammographic energy range.