The objective of this research project was to establish a better understanding of the mechanism(s) and route(s) by which selenium (Se) may enter an aquatic ecosystem that has been receiving treated metal mine effluent from an upstream uranium milling operation. Synchrotron based X-ray absorption spectroscopy (XAS) and X-ray fluorescence (XRF) imaging, which require little sample pre-treatment, were employed to study the speciation and distribution of Se in complex sediment and benthic invertebrates samples collected from the field. Laboratory based inductively coupled plasma mass spectrometry (ICP-MS) provided quantitative Se concentrations. Samples were taken from Fox Lake and Unknown Lakes, downstream of the mill, and Yeoung Lake as a control. The variation in Se speciation as a function of depth in intact sediment cores may provide insight into the species of Se available to the sediment dwelling benthic invertebrate communities. Therefore, a custom sample holder was designed to facilitate analysis of intact sediment cores at cryogenic temperatures. Additionally, laboratory reared chironomids were water-exposed to various Se species, to compare their Se speciation and localization to chironomids collected in the field. The successful demonstration of the custom sample holder and viable use of synchrotron XAS and XRF in studying sediment and chironomid samples have revealed that biologically relevant Se forms were present in sediment at depths accessible by the benthic invertebrate community. These Se forms included selenomethionine-like and selenite species, and to a lesser degree elemental Se; an increased proportion of reduced Se species was observed as depth increased. Other elements measured concurrently with Se included As, Zn, Cu, Ni, Fe, and Mn, providing an estimation of the redox boundary found both in Fox and Unknown Lake, as well as suggesting the presence of iron species that could aid in the reduction of Se. Field and laboratory reared chironomids showed similar Se species, and XRF imaging revealed the localization of Se in 4 distinct regions: head capsule, brain, salivary glands, and gut lining. Overall, the project has provided important insights into the interactions of Se with this aquatic ecosystem, which may have future applications in cold water systems with elevated Se concentrations.

Mercury (Hg) compounds are some of the most toxic compounds of any heavy metal on earth. Due to long-range transport from point sources Hg can be found world-wide in air, soil, water, and living organisms. Mercury compounds can cause a number of adverse effects, with the unborn fetus, infants, and children being most susceptible. Zebrafish (Danio rerio) are an excellent vertebrate model system for toxicological studies, including developmental effects. The overall objective of this research was to investigate the effects of inorganic forms of Hg in zebrafish larvae. Unique accumulation patterns were observed using synchrotron X-ray fluorescence imaging after zebrafish were exposed to one of four Hg compounds (i.e. mercuric chloride, mercury bis-L-cysteineate, methylmercury chloride, methylmercury L-cysteineate). Specifically, we noted chemical form dependant and tissue-specific Hg accumulation including the sensory cells of the olfactory epithelia and the neuromasts. Phenylthiourea (PTU) is commonly used to block zebrafish melanogenesis to generate transparent larvae to aid with enhanced visualization of immunohistochemical and vital stains. It was determined that PTU dramatically alters Hg toxicity through chemical interaction with Hg so that further studies were conducted in the absence of PTU. To investigate the effects of Hg on primary neurons, the immunohistochemistry protocol using anti-acetylated tubulin was performed and the results demonstrated that mercuric chloride damages primary neurons particularly in the olfactory pits. To study potential detoxification of Hg in zebrafish we examined the efficacy of two sequestration agents, dimercaptosuccinic acid and alpha lipoic acid, as well as endogenous selenium. The levels of Hg were not significantly lower following treatment with either sequestration agent under the conditions used in this research. Previous work examining the antagonistic relationship between Hg and selenium has been conducted by dosing animals with both Hg and selenium (Se). We discovered a mixed chalcogenide of the general form HgSxSe(1-x) forming in vivo following exposure to mercuric chloride without the addition of selenium. Indeed the selenium may have been remobilized from natural stores in the pigment spots. The research presented herein demonstrates that the target tissues for Hg depend strongly on chemical form. In particular inorganic Hg can accumulate in a number of important tissues including sensory systems. The formation of insoluble and non-toxic HgSxSe(1-x) in zebrafish larvae suggests that endogenous selenium may play critical roles in modulating toxicity.

GEMs (Gas Electron Multiplier) and Thick-GEMs (Thick-Gas Electron Multiplier) are MPGDs (Micropattern Gas Detector) that make part of the new generation of gaseous detectors, allowing high counting rates, low cost when compared to solid state detectors, high radiation hardness and gain when using multiple structures. Besides that, the handling and maintenance of these detectors is relatively simple, being versatile to detect different types of radiation. Therefore, these detectors are an effective alternative to build imaging systems with large sensitive area. This work consists in the study and characterization of a set of gaseous detectors, more specifically the Thick-GEMs produced in the High Energy Physics and Instrumentation Center at IFUSP, which were tested showing promising results in terms of gain, energy resolution and operational stability. However, due to the low signal-to-noise ratio of the Thick-GEMs, the X-ray fluorescence imaging system was mounted using GEMs. During this work the necessary software tools for image processing and reconstruction were developed as a parallel study in computational simulations to better understand the operation of gaseous detectors. X-ray fluorescence techniques are essential in areas such as medicine and the study of historical and cultural heritage since they are non-invasive and non-destructive. Techniques to check the authenticity of masterpieces are required and museums are gradually becoming more interested in the Physics and instrumentation needed to characterize their patrimony. / Os GEMs (Gas Electron Multiplier) e Thick-GEMs (Thick-Gas Electron Multiplier) são estruturas do tipo MPGD (Micropattern Gas Detector) que fazem parte da nova geração de detectores de radiação a gás e permitem altas taxas de contagens, baixo custo quando comparados com os detectores de estado sólido, uma elevada resistência à radiação e ganhos elevados, quando utilizadas estruturas múltiplas para multiplicação. Além disso, o manuseio e manutenção desses detectores é relativamente simples, sendo versáteis em relação à montagem podendo detectar diferentes tipos de radiação. Sendo assim, a utilização desses detectores é uma alternativa eficiente para montar um sistema de imagem com grande área sensível. Este trabalho consiste no estudo e caracterização de um conjunto de detectores gasosos, mais especificamente os Thick-GEMs produzidos pelo grupo de Física de altas energias e Instrumentação do IFUSP, que foram testados para serem empregados em um sistema de imagem de fluorescência de raios-X. Os Thick-GEMs testados apresentaram resultados promissores em termos de ganho, resolução em energia e estabilidade operacional. No entanto, devido à baixa relação sinal-ruído, um sistema de imagem de fluorescência de raios-X foi montado utilizando GEMs. Durante o trabalho as ferramentas de software necessárias para processamento e reconstrução de imagens foram desenvolvidas, assim como um estudo paralelo de simulações computacionais para entender melhor o funcionamento de detectores gasosos. Técnicas como o imageamento por fluorescência de raios-X são de suma importância pois são consideradas não invasivas e não destrutivas. Sua utilização tem uma importância imprescindível nas áreas da medicina e na análise de patrimônios histórico e cultural. Atualmente, a verificação e validação de autenticidade de obras é um requisito obrigatório e alguns museus começam a se interessar cada vez mais em áreas da Física e da instrumentação necessária para caracterizar o seu patrimônio.

GEMs (Gas Electron Multiplier) and Thick-GEMs (Thick-Gas Electron Multiplier) are MPGDs (Micropattern Gas Detector) that make part of the new generation of gaseous detectors, allowing high counting rates, low cost when compared to solid state detectors, high radiation hardness and gain when using multiple structures. Besides that, the handling and maintenance of these detectors is relatively simple, being versatile to detect different types of radiation. Therefore, these detectors are an effective alternative to build imaging systems with large sensitive area. This work consists in the study and characterization of a set of gaseous detectors, more specifically the Thick-GEMs produced in the High Energy Physics and Instrumentation Center at IFUSP, which were tested showing promising results in terms of gain, energy resolution and operational stability. However, due to the low signal-to-noise ratio of the Thick-GEMs, the X-ray fluorescence imaging system was mounted using GEMs. During this work the necessary software tools for image processing and reconstruction were developed as a parallel study in computational simulations to better understand the operation of gaseous detectors. X-ray fluorescence techniques are essential in areas such as medicine and the study of historical and cultural heritage since they are non-invasive and non-destructive. Techniques to check the authenticity of masterpieces are required and museums are gradually becoming more interested in the Physics and instrumentation needed to characterize their patrimony. / Os GEMs (Gas Electron Multiplier) e Thick-GEMs (Thick-Gas Electron Multiplier) são estruturas do tipo MPGD (Micropattern Gas Detector) que fazem parte da nova geração de detectores de radiação a gás e permitem altas taxas de contagens, baixo custo quando comparados com os detectores de estado sólido, uma elevada resistência à radiação e ganhos elevados, quando utilizadas estruturas múltiplas para multiplicação. Além disso, o manuseio e manutenção desses detectores é relativamente simples, sendo versáteis em relação à montagem podendo detectar diferentes tipos de radiação. Sendo assim, a utilização desses detectores é uma alternativa eficiente para montar um sistema de imagem com grande área sensível. Este trabalho consiste no estudo e caracterização de um conjunto de detectores gasosos, mais especificamente os Thick-GEMs produzidos pelo grupo de Física de altas energias e Instrumentação do IFUSP, que foram testados para serem empregados em um sistema de imagem de fluorescência de raios-X. Os Thick-GEMs testados apresentaram resultados promissores em termos de ganho, resolução em energia e estabilidade operacional. No entanto, devido à baixa relação sinal-ruído, um sistema de imagem de fluorescência de raios-X foi montado utilizando GEMs. Durante o trabalho as ferramentas de software necessárias para processamento e reconstrução de imagens foram desenvolvidas, assim como um estudo paralelo de simulações computacionais para entender melhor o funcionamento de detectores gasosos. Técnicas como o imageamento por fluorescência de raios-X são de suma importância pois são consideradas não invasivas e não destrutivas. Sua utilização tem uma importância imprescindível nas áreas da medicina e na análise de patrimônios histórico e cultural. Atualmente, a verificação e validação de autenticidade de obras é um requisito obrigatório e alguns museus começam a se interessar cada vez mais em áreas da Física e da instrumentação necessária para caracterizar o seu patrimônio.