Dissertations / Theses on the topic 'Mercury'

Mercury is a collection of short stories based in the fictional town of Mercury, Georgia. Set over the course of several decades, the stories trace the events that changed individuals, families, and a whole community for decades. Loosely based on the author's real-life family history, the stories, both humorous and heartbreaking, show characters caught between the past and the present and searching for a way forward. A girl who makes friends with a ghost, a woman who can't help but run from crying babies, a man forced to face the town's darkest side—these and other characters respond in surprising ways to circumstances that are both ordinary and extraordinary. Most of the stories in the collection are linked, showing the interconnectedness of the lives in this small town. The pieces work together to present a larger narrative of how the characters and the town struggle to change, survive, hope, and face the future.
M.F.A.
Masters
English
Arts and Humanities
Creative Writing

Les tourbières sont communément utilisées comme archives de dépôts de mercure (Hg). De nombreuses études ces dernières décennies ont montré que les taux d’accumulation de Hg (HgARs) ont augmenté en réponse à l’industrialisation. Les signatures isotopiques en Hg se révèlent très utiles pour mieux caractériser les dépôts de Hg. Elles ont permis de montrer que les dépôts secs de Hg élémentaire gazeux (GEM) dominent les dépôts de Hg sur la tourbière du Pinet. L’analyse d’échantillons de tourbe provenant de plusieurs tourbières en hémisphère nord montre que les dépôts secs de GEM dominent globalement les dépôts de Hg. Les tourbières pourraient donc être utilisées comme archives à la fois des dépôts humides et des concentrations en GEM pendant l’Holocène. On présente la première reconstruction quantitative des concentrations passées en GEM à partir de carottes de tourbe. L’impact de l’Homme sur le cycle du Hg a eu pour conséquence une augmentation graduelle des concentrations en GEM de 0,2 (10 000 – 4000 BP) à 3,5 ng m-3 (20ème siècle), accompagnée par des modifications de signatures isotopiques du Hg atmosphérique. Cette première utilisation de tourbières comme archives de concentration et d’isotopie du GEM est prometteuse, et devrait être étendue à la période pré-anthropique pour étudier les variations naturelles du cycle du Hg pendant l’Holocène
During the past few decades, peatlands were successfully used to investigate historical mercury (Hg) deposition. The chronology of Hg accumulation rates (HgARs) to peatlands is well constrained, with recent increases in HgAR associated with anthropogenic Hg emissions and deposition. The use of Hg stable isotopes in peatland ecosystems provides new opportunities to better characterize and understand historical Hg deposition. In an extensive study conducted at the Pinet peat bog (French Pyrenees) we identify gaseous elemental Hg (GEM) dry deposition, via foliar uptake, as the dominant Hg transfer pathway from the atmosphere to peat vegetation. Based on the Hg isotope analysis of multiple northern hemispheric peat records, we find that GEM dry deposition dominates Hg deposition globally. We suggest that peatlands can be used as archives of both past Hg wet deposition, Hg dry deposition and GEM concentration. We present the first quantitative reconstruction of historical atmospheric GEM concentrations using peat archives from the Pyrenees. The Human impact on Hg cycling caused a gradual increase in GEM concentrations from 0.2 (10,000 – 4000 BP) to 3.5 ng m-3 (20th Century) and was accompanied by a change in atmospheric Hg isotope signatures. This first comprehensive study on Hg isotope deposition to peatlands is promising and should be extended to pre-anthropogenic times to investigate natural variations in atmospheric Hg dynamics during the Holocene

This thesis examines the production and distribution of dissolved gaseous mercury (DGM) in freshwater ecosystems and its relationship to mercury volatilization. The importance of volatilization was assessed within a multidisciplinary mercury mass balance for Big Dam West Lake (BDW) Kejimkujik Park, Nova Scotia. The magnitude of volatilization was found to be approximately double the direct wet deposition over lake and wetlands, and 27% of the direct wet deposition to the terrestrial catchment. Over the entire basin area the mass of mercury volatilized is 46% of the mass deposited by wet deposition. A new method of continuous (5 minute) DGM analysis was developed and tested. The detection limit for DGM was 20 fmol L-1 with 99% removal efficiency. Control experiments showed that there was no interference due to methyl mercury, which is present in similar concentrations to DGM. Experiments comparing continuous DGM analysis with discrete DGM analysis showed that the results are not significantly affected by typical variations in water temperature (4--30°C), oxidation-reduction potential (135--355 mV), dissolved organic carbon (4.5--10.5 mg L-1), or pH (3.5--7.8). The continuous analysis was within 4.5% of the discrete analysis when compared across 12 samples analyzed in triplicate. Diurnal patterns for dissolved gaseous mercury (DGM) and mercury flux were measured (using this new DGM method and a Teflon flux chamber method) in two lakes with contrasting dissolved organic carbon (DOC) concentrations in Kejimkujik Park, Nova Scotia. Consistently higher DGM concentrations were found in the high DOC lake as compared to the low DOC lake. Cross-correlation analysis indicated that DGM dynamics changed in response to solar radiation with lag-times of 65 and 90 minutes. An examination of current mercury flux models using this quantitative data indicated some good correlations between the data and predicted flux (r ranging from 0.27 to 0.83) but generally poor fit (standard deviation of residuals ranging from 0.97 to 3.38). This research indicates that DOC and wind speed may play important roles in DGM and mercury flux dynamics that have not been adequately accounted for in current predictive models. The distribution of DGM in the water columns of shallow and deep freshwater lakes was investigated in Lake Ontario and several small freshwater lakes. When DGM concentrations were expressed on an areal basis, DGM concentrations above the thermocline in Lake Ontario average 1.5 ng m-2 and in small freshwater lakes it ranged between 0.1 and 0.8 ng m -2. Further, it was demonstrated that the majority of DGM in large freshwater lakes such as Lake Ontario exists below the thermocline where photochemical oxidation and reduction processes cannot occur. The depth profiles indicate that vertical mixing in the water column may alter the DGM concentration in the upper epilimnion, and that turn over in deep lakes may result in a transfer of large concentrations of DGM from the hypolimnion into the epilimnion. In addition, the results indicate that microbial processes may be an important factor regulating DGM in the water column of freshwater lakes, particularly in the hypolimnion. (Abstract shortened by UMI.)

Mestrado em Biologia Marinha
Mercury (Hg) is classified as a pollutant of primary importance because of its high degree of toxicity, persistence and bioaccumulative properties, especially in the aquatic environment. It is released from natural and anthropogenic sources, and once in the environment, the inorganic Hg can be converted in to organic Hg (Methylmercury – MeHg) through bacterial processes. MeHg tends to bioaccumulate and biomagnify through the food web, representing a serious risk to human health. Due to the health risks of excessive Hg exposure, international agencies such as the USEPA (United States Environmental Protection Agency) have established safety levels (reference doses (RfD)) of daily exposure, being the Hg concentration present in human hair used to estimate MeHg exposure. Fish is an important component of a healthy diet for the human population and the fish consumption is expected to be relatively stable in the next two decades; however, fish is also considered a major source of MeHg exposure to human population. The key question of the present study was evaluating the Hg bioaccumulation in humans based in fish consumption. Specific tasks were delineated: (i) evaluatue the human exposure to Hg via fish consumption using a food frequency questionnaire, (ii) assess Hg exposure through Hg measurement in the hair, (iii) evaluate the Hg intake levels, through the application of formulas established by the World Health Organization, (iv) review fish consumption data, Mercury Tolerable intake values and Hg content in fish, based in several reports from Food and Agriculture Organization and European Union and (v) calculation and establishment of isocurves describing the maximum number of fishmeal per week without exceeding the MeHg Rfd (USEPA RfD), by combining number of meals (per week), amount of fish ingested (by meal) and levels of MeHg in fish. Overall data indicate that individuals consuming the highest number of fishmeals per week, also generally showed increased Hg levels in the scalp hair; however, the risk alert of the mercury exposure should not be considered. The real (quantified) and potential (extrapolated) Hg levels in human scalp of adolescents diverge as fish consumption increases, being the effective Hg uptake lower than the expected levels, emphasizing the ability of the human body to induce a self protection response, meaning that MeHg assimilation is probably minimized by detoxification mechanisms. As a final remark, considering the intake of Hg through fish consumption as the main route exposure, the study points out that even a small meal of 50g fish with 0.84 μg g-1 of MeHg per week would reach the USEPA RfD levels, despite the 1.0 μg g-1 of MeHg in fish are being allowed in fish consumption.
O Mercúrio (Hg) é classificado como um dos poluentes mais importantes devido ao seu alto grau de toxicidade, persistência e à sua capacidade de bioacumulação, especialmente no ambiente aquático. Este é libertado a partir de fontes naturais e antropogénicas, e uma vez no ambiente, o Hg inorgânico libertado pode ser convertido em Hg orgânico (metilmercúrio - MeHg) através de processos bacterianos. O MeHg tende a bioacumular e a biomagnificar ao longo da cadeia trófica, representando um sério risco para a saúde humana. Devido a estes riscos resultantes da exposição excessiva ao Hg, agências internacionais, como a USEPA (Agência de Proteção Ambiental dos Estados Unidos) estabeleceram níveis de segurança (doses de referência (DRf)) de exposição diária, sendo a concentração de Hg presente no cabelo humano utilizada para estimar esta exposição. O peixe é uma componente importante de uma dieta saudável para a população humana e o consumo de peixe deverá ser relativamente estável nas próximas duas décadas. No entanto, o peixe também é considerado uma das principais fontes de exposição a MeHg para a população humana. Este estudo teve como questão central a avaliação da bioacumulação de Hg em humanos face ao padrão de consumo de peixe, sendo delineados os seguintes objetivos específicos: (i) avaliar a exposição humana ao Hg face ao consumo de peixe utilizando um questionário de frequência alimentar, (ii) avaliar a exposição ao Hg através da quantificação de Hg no cabelo humano, (iii) avaliar os potenciais níveis de ingestão de Hg, através da aplicação de fórmula estabelecida pela Organização Mundial de Saúde, (iv) rever dados de consumo de peixe, valores de ingestão de Hg e conteúdo de Hg em peixes, com base em vários relatórios da Organização das Nações Unidas para a Alimentação e Agricultura, assim como, da União Europeia e (v) calcular linhas de tendência (isocurvas) descrevendo o número máximo de refeições de peixe por semana, sem exceder a DRf para o MeHg (USEPA DRf), combinando o número de refeições de peixe (por semana), a quantidade de peixe ingerido (por refeição) e a [MeHg] no peixe consumido. Os resultados revelam que os indivíduos que indicaram consumir um maior número de refeições de peixe por semana, também apresentam em regra níveis mais altos de Hg no cabelo; no entanto, o risco de alerta para a exposição ao Hg não deve ser considerado. Os níveis reais (quantificados) e valores potenciais (extrapolados) de Hg no cabelo dos adolescentes divergiram quando aumentou o consumo de peixe, sendo menor a absorção de Hg real comparativamente ao valor esperado, dando relevo à capacidade do corpo humano induzir uma resposta de auto-protecção, sendo a absorção de MeHg provavelmente minimizada por mecanismos de desintoxicação. O estudo salienta que mesmo uma pequena refeição de 50g de peixe com 0,84 μg g-1 de MeHg por semana alcançaria do valor estabelecido para a ingestão de MeHg (DRf USEPA), apesar de ser permitido o consumo de peixe com valores de 1,0 μg g-1 de MeHg.

Els oceans conten aproximadament un total de 10^29 cèl·lules microbianes. Els bacteris marins són responsables de la major part de la respiració que es produeix en l’oceà i són essencials en els cicles biogeoquímics de la Terra. Estudiar la diversitat bacteriana dels ecosistemes marins i tenir accés als genomes mitjançant estudis dependents o independents de cultiu és important per desxifrar el potencial metabòlic dels bacteris marins. El cultius ens aporten informació sobre la fisiologia bacteriana, ecologia i contingut genòmic, però la majoria dels esforços en aïllar bacteris marins provenen de la zona fòtica de l’oceà, deixant les profunditats marines menys explorades. En aquesta tesi, tècniques estàndard de cultiu han permès crear una col·lecció marina de cultius de bacteris heterotròfics (MARINHET), composada per més de 2000 aïllats, recuperats de diverses regions oceanogràfiques, de diverses profunditats (superfície, mesopelàgic i batipelàgic) i cobrint diverses estacions i anys. El Capítol 1 descriu la seva taxonomia, diversitat filogenètica i biogeografia i revela que un 37% de les soques aïllades són 100% idèntiques en el gen ribosomal 16S (16S rRNA) entre la zona fòtica (superfície) i afòtica (mesopelàgic i batipelàgic). A més, hem identificat Alteromonas i Erythrobacter entre els gèneres marins heterotròfics més comuns que recuperem en cultiu usant un medi marí estàndard. Les tècniques tradicionals de cultiu generalment només recuperen una fracció petita de les comunitats bacterianes naturals, fenomen conegut com ‘la gran anomalia de recompte en placa’ i moltes de les soques que s’aïllen pertanyen a la biosfera rara. Tanmateix, no coneixem si aquests patrons, normalment descrits per als bacteris de la zona fòtica, també s’apliquen als bacteris de les profunditats. En el Capítol 2 he combinat els resultats obtinguts mitjançant tècniques dependents i independents de cultiu comparant les seqüències del 16S rRNA de la col·lecció MARINHET contra fragments de seqüenciació massiva del 16S rRNA, tant d’amplicons com de metagenomes, obtinguts de mostres globalment distribuïdes i de diferents profunditats. Trobem que una major proporció dels bacteris de l’oceà profund són cultivables i una fracció important dels aïllats té preferència a un estil de vida adherit a partícules. A més, confirmem que el dogma ‘menys de l’1% dels bacteris són cultivables’ ha de ser revisat ja que trobem variabilitat en les mostres de l’oceà profund, on fins a un 3% de les cèl·lules han sigut cultivades. Els aïllats bacterians són un excel·lent material per a aplicacions biotecnològiques com la bioremediació de zones marines contaminades. El mercuri és un metall pesat tòxic i la seva forma més perillosa, el metilmercuri (MeHg), es bioacumula a la cadena tròfica marina. No obstant això, es coneix molt poc la tolerància de bacteris marins enfront del mercuri o la fisiologia d’aquelles soques que codifiquen l’operó dels gens de resistència (operó mer). El Capítol 3 descriu els resultats del mapeig funcional dels gens merA i merB, clau en la detoxificació, en una fracció de la col·lecció MARINHET. Ens centrem en dos generes marins, amb un potencial genètic per a la degradació del mercuri conegut, com són Alteromonas i Marinobacter. Revelem que els gens merAB estan àmpliament distribuïts en diferents regions oceanogràfiques i en diverses profunditats. Addicionalment, hem seleccionat una soca d’ Alteromonas mediterranea per a futurs estudis de bioremediació degut a la seva alta tolerància i capacitat de degradació de diferents formes de mercuri.
Los océanos contienen aproximadamente un total de 10^29 células microbianas. Las bacterias marinas son responsables de la mayor parte de la respiración que se produce en el océano y son esenciales en los ciclos biogeoquímicos de la Tierra. Estudiar la diversidad bacteriana de los ecosistemas marinos y tener acceso a los genomas mediante estudios dependientes e independientes de cultivo es importante para descifrar el potencial metabólico de las bacterias marinas. Los cultivos nos aportan información sobre la fisiología bacteriana, ecología y contenido genómico, pero la mayoría de los esfuerzos en aislar bacteria marinas provienen de la zona fótica del océano, dejando las profundidades marinas menos exploradas. En esta tesis, técnicas estándar de cultivo han permitido crear una colección marina de bacterias heterótrofas (MARINHET), compuesta por más de 2000 aislados, recuperados de varias regiones oceanográficas, de varias profundidades (superficie, mesopelágico y batipelágico), y cubriendo varias estaciones y años. El Capítulo 1 describe su taxonomía, diversidad filogenética y biogeografía y revela que un 37% de las cepas son 100% idénticas en la secuencia parcial del gen ribosomal 16S (16S rRNA) entre la zona fótica (superficie) y afótica (mesopelágico y batipelágico). Además, hemos identificado Alteromonas y Erythrobacter entre los géneros marinos heterótrofos más comunes que recuperamos en cultivo usando un medio marino estándar. Las técnicas tradicionales de cultivo generalmente solo recuperan una fracción pequeña de las comunidades bacterianas naturales, fenómeno conocido como ‘la gran anomalía de recuento en placa’ y muchas de las cepas que se aíslan pertenecen a la biosfera rara. Sin embargo, no conocemos si estos patrones, normalmente descritos para las bacterias de superficie, también se aplican en las profundidades. En el Capítulo 2 he combinado resultados obtenidos mediante técnicas dependientes e independientes de cultivo comparando las secuencias del 16S rRNA de la colección MARINHET contra los fragmentos de secuenciación masiva del 16S rRNA (de amplicones y metagenomas), obtenidos de muestras globalmente distribuidas y de diferentes profundidades. Una mayor proporción de las bacterias del océano profundo son cultivables y una fracción importante de los aislados tiene preferencia a un estilo de vida adherido a partículas. Además, confirmamos que el dogma ‘menos del 1% de las bacterias son cultivables’ deber ser revisado ya que encontramos variabilidad en las muestras de profundidad, donde hasta un 3% de las células se han podido aislar. Los aislados bacterianos son un excelente material para aplicaciones biotecnológicas, como la biorremediación de zonas marinas contaminadas. El mercurio es un metal pesado tóxico y su forma más peligrosa, el metilmercurio (MeHg), se bioacumula en la cadena trófica marina. No obstante, se conoce muy poco la tolerancia de bacterias marinas frente al mercurio o la fisiológia de aquellas cepas que codifican los genes de resistencia (operón mer). El Capítulo 3 describe los resultados del mapeo funcional de los genes merA y merB, clave en la detoxificación, en una fracción de la colección MARINHET. Nos centramos en dos géneros marinos, con un potencial genético para la degradación del mercurio previamente descrito en la literatura, como son Alteromonas y Marinobacter. Desvelamos que los genes merAB están ampliamente distribuidos en diferentes regiones oceanográficas y en varias profundidades. Adicionalmente, hemos seleccionado una cepa de Alteromonas mediterranea para futuros estudios de biorremediación debido a su alta tolerancia y capacidad de degradación de diferentes formas de mercurio.
The world’s oceans sustain the life for an estimated total of 10^29 microbial cells. Marine bacteria are responsible for most part of the ocean respiration and are key in most biogeochemical cycles of the Earth. Accordingly, the study of the bacterial diversity present in different marine ecosystems is essential, and having access to their genomes through isolation or genomic centric studies is important to decipher their metabolic potential. Isolation of marine microorganisms is fundamental to gather information about their physiology, ecology and genomic content. To date, most of the bacterial isolation efforts have focused on the photic ocean leaving the deep ocean less explored. In this thesis, standard plating techniques allowed to create a marine culture collection of heterotrophic bacteria (MARINHET). More than 2000 isolates were retrieved from samples collected from a variety of oceanographic regions, from different depths including surface, mesopelagic and bathypelagic waters, and also covering different seasons and years. Chapter 1 describes the taxonomy, the phylogenetic diversity and the biogeography of culturable heterotrophic marine bacteria, and reveals that an important percentage of the strains (37%) are 100% identical in their partial 16S rRNA gene between photic and aphotic layers. In addition, we identified Alteromonas and Erythrobacter genera as the most frequently retrieved heterotrophic bacteria from the ocean in standard marine agar medium. It is a long-standing observation that traditional culture techniques only retrieve a small fraction of the microbial diversity found in natural environments including marine ecosystems, what is known as ‘the great plate count anomaly’. In addition, most of the retrieved isolates belong to the so-called rare biosphere. However, we do not know if these patterns, usually described for bacteria living in the photic ocean, also apply for the deep ocean bacteria. In Chapter 2 of this thesis, I combined results from culture-dependent and -independent techniques by comparing the 16S rRNA partial sequences of the MARINHET isolates with 16S rRNA amplicon Illumina TAGs (16S iTAGs) and metagenomic TAGs (miTAGs) from surface, mesopelagic and bathypelagic samples globally distributed. A high proportion of bacteria inhabiting the deep ocean could be retrieved by pure culture techniques and a significant fraction of the isolates preferred a lifestyle attached to particles. Additionally, I revised the axiom that ‘less than 1% of bacteria can be cultured’, finding variability between mesopelagic and bathypelagic samples, where up to 3% of the cells could be cultured. Bacterial isolates also represent a valuable genetic reservoir for biotechnology applications, such as bioremediation strategies of marine polluted environments. Mercury is one of the most toxic heavy metals in the planet and its most dangerous form, methylmercury (MeHg), is being bioaccumulated in the marine food web. However, little is known about the tolerance capacity and phenotypic characterization of marine bacteria codifying the mercury resistance operon (mer operon). Chapter 3 describes the functional screening of merA and merB genes, which are key in the mercury detoxification process, in well know marine genera with described genetic potential for mercury detoxification, such as Alteromonas and Marinobacter. I reported that the merAB genes from these two genera are widely distributed in different oceanographic regions and depths. In addition, I selected a promising candidate, phylogenetically affiliated to Alteromonas mediterranea, for future bioremediation studies due to its high tolerance and degradation ability of different mercury forms.
Universitat Autònoma de Barcelona. Programa de Doctorat en Microbiologia

Several molecules previously produced from a nitrile-based cascade cyclization were examined as potential mercury sensors. Various analytical parameters, including fluorescence quantum yield, UV shift, fluorescence quenching, binding constant, binding ratio, and lowest detection limit, were measured. The best mercury sensor molecule was found to be molecule 3c, which could be easily synthesized in gram quantities (3 steps, 55% overall yield). This molecule has a very high fluorescence quantum yield (Φ = 0.87), high sensitivity and selectivity towards mercury ion in both organic and aqueous media. The overall performance of molecule 3c is as good as, or better than, the majority of organic dye based mercury sensors reported to date.

Introduction: A mercury fact sheet that contains essential information and can be clearly understood by majority of adults is needed. In Fiscal Year 2009, EPA responded to more releases related to mercury than any other release. Since 2003, EPA has responded to more than 200 mercury releases. The American Association of Poison Control Centers estimate more than 50,000 people have been exposed to mercury vapors from 2003 to 2008, and 19,000 mercury cleanups have occurred from 2006 to 2008. Purpose: To determine what information needs to be included in a mercury fact sheet and how it should be created to inform adults who may be important in preventing and limiting exposure during accidental mercury release in the United States. Methods: The Flesch-Kincaid Grade Level Formula Data and the Suitability Assessment of Materials (SAM) tool were used to determine readability and appropriateness of twelve fact sheets related to elemental mercury. Length of fact sheets and illustration coverage percentage were also assessed. In addition, surveys were performed with four people who were involved in response to mercury releases in 2007 to 2009. The information they provided was also summarized to determine important elements that should be included in the fact sheets. Results: Information in a fact sheet should include the background of mercury, procedures in the event of a release, and ways to prevent releases. Based on the Flesch-Kincaid Grade Level, the literacy levels required to comprehend the 12 facts sheets was 11.4 on average. The majority of adults cannot comprehend the twelve fact sheets evaluated. Based on the evaluation of the material using SAM, none of the fact sheets scored higher than adequate with SAM. Only two fact sheets were written on one page and none of the fact sheets used relevant, simple illustrations with captions. Discussion: An effective mercury fact sheet needs to be about one page long and focuses on background, procedures, and prevention of exposure during a mercury release. Information obtained from interviews found that people focused the majority of their attention on the first page only. The fact sheet needs to be written at a sixth grade reading and to be able to receive a superior rating when assessed with SAM. This will ensure that the fact sheet is readable and comprehendible by the majority of adults and include the necessary information that the public must know regarding mercury. A new fact sheet was developed and assessed using both Flesch-Kincaid level and SAM and was found to have a 6.6 reading grade level and received a superior score under SAM. This fact sheet will be used by EPA along with the existing more comprehensive fact sheets at state agencies, and poison control centers for future releases and will be given to schools to educate and prevent future releases.

Thesis (Ph.D.)--University of Cincinnati, 2007.
Advisor: Tim C. Keener. Title from electronic thesis title page (viewed Feb. 18, 2008). Keywords: Magicicada; cassinii; septendecium; septendecula; mercury in soils; mercury in adult insects; mercury in terrestrial insects; mercury in roots; exuviae; combustion AA; CVAAS; mercury in exuviae; mercury in insects. Includes abstract. Includes bibliographical references.

Data from MESSENGER and the GOES solar activity archive are used to deduce properties of Mercury and its X-ray environment in preparation for the forthcoming ESA/JAXA BepiColombo mission to Mercury. Data from MESSENGER’s X-ray spectrometer operations at Mercury exhibit background X-ray enhancements which are identified as the results of astrophysical sources crossing the instrument field of view and of electron bombardment of the X-ray spectrometer causing fluorescence within the instrument. These electron enhancements are analysed and mapped, leading to a three-dimensional representation of low-energy electron populations in the Mercury environment, the distributions of which are associated with features of Mercury’s magnetosphere, including the sunward magnetopause and magnetic equator. The population is characterised, producing estimates of low-energy electron number densities which are consistent with previous observations. Thus, the X-ray spectrometer functions as a proxy detector for electrons with energies below the threshold of dedicated electron detectors. Variations in seasonal X-ray background flux observed by the MESSENGER X-ray spectrometer are investigated, with a modulation visible with a periodicity of one Mercury year. Several telemetry parameters, including temperature, show corresponding variations. The origin of the variation in background flux is identified as the calculation in spacecraft telemetry relating instrument live time to instrument integration time, which varies on the same yearly period. The GOES solar activity archive is used to generate a model of solar X-ray flux levels, with the intention of providing an estimate of the levels of X-ray flux the BepiColombo mission will encounter, and subsequently the volume and rate of data that the MIXS instrument will produce. This model is used to predict the likelihood of the instrument experiencing data loss events by exceeding the data storage available, and how this likelihood varies with the level of solar flux and the onboard storage space that is allocated to the instrument.

Tissue samples from spotted gar (Lepisosteus oculatus) and largemouth bass (Micropterus salmoides) were collected from Caddo Lake. Gar and bass livers were subjected to histological investigation and color analysis. Liver color (as abs at 400 nm) was significantly correlated with total mercury in the liver (r2 = 0.57, p = 0.02) and muscle (r2 = 0.58, p = 0.01) of gar. Evidence of liver damage as lipofuscin and discoloration was found in both species but only correlated with liver mercury concentration in spotted gar. Inorganic mercury was the predominant form in gar livers. In order to determine the role of mercury speciation in fish liver damage, a laboratory feeding study was employed. Zebrafish (Danio rerio) were fed either a control (0.12 ± 0.002 µg Hg.g-1 dry wt), inorganic mercury (5.03 ± 0.309 µg Hg.g-1 dry wt), or methylmercury (4.11 ± 0.146 µg Hg.g-1 dry wt) diet. After 78 days of feeding, total mercury was highest in the carcass of zebrafish fed methylmercury (12.49 ± 0.369 µg Hg.g-1 dry wt), intermediate in those fed inorganic mercury (1.09 ± 0.117 µg Hg.g-1 dry wt), and lowest in fish fed the control diet (0.48 ± 0.038 µg Hg.g-1 dry wt). Total mercury was highest in the viscera of methylmercury fed zebrafish (11.6 ± 1.86 µg Hg.g-1 dry wt), intermediate in those fed inorganic diets (4.3 ± 1.08 µg Hg.g-1 dry wt), and lowest in the control fish (below limit of detection). Total mercury was negatively associated with fish length and weight in methylmercury fed fish. Condition factor was not associated with total mercury and might not be the best measure of fitness for these fish. No liver pathologies were observed in zebrafish from any treatment.

Thesis (M.D.S.)--University of Sydney, 1992.
Title from title screen (viewed Apr. 23, 2009) Submitted in fulfilment of the requirements for the degree of Master of Dental Surgery to the Faculty of Dentistry. Degree awarded 1992; thesis submitted 1991. Includes bibliography. Also available in print form.

The safety of amalgam restorations has been challenged, claims having been made that health risks are associated with the constituent mercury. There are assertions that mercury released from amalgam produces mercury poisoning, and is thus responsible for diverse symptoms of impaired health as well as disease states such as Multiple Sclerosis. This study examines the various forms of mercury and their effects and attempts particularly to delineate the significance of dental amalgam as a factor in hypersensitivity reactions and in the human body burden of mercury. Dental personnel are evaluated as a potentially high-risk group for mercury exposure. Dental amalgam and alternative restorative materials are considered, the removal of amalgam being evaluated as a therapeutic modality. The “anti-amalgam” perspective is scrutinised and the validity of the claims assessed. A review of the scientific literature, and the statements of national and international dental and scientific literature, and the statements of national and international dental and scientific organisations reflect the general support for the safety of dental amalgam. There is no evidence that health risks are associated with the use of dental amalgam other than rare local allergic reactions and oral lichenoid lesions. Notwithstanding the usefulness and safety of dental amalgam certain recommendations and conclusions are made in respect of future approaches to the utilisation of this material and for mercury in general. Further objective scientific research is necessary to determine the effects on human health of chronic exposure to low levels of mercury. There is the need for accurate general population threshold levels to be established for mercury vapour with special consideration for the vulnerable members of the community. The health professions have a significant role to play in providing informed opinion and advice for their patients and the public, in countering the more eccentric claims of the anti-amalgamists and assuaging the anxiety and confusion which accompanies this subject.

Master of Dental Surgery
The safety of amalgam restorations has been challenged, claims having been made that health risks are associated with the constituent mercury. There are assertions that mercury released from amalgam produces mercury poisoning, and is thus responsible for diverse symptoms of impaired health as well as disease states such as Multiple Sclerosis. This study examines the various forms of mercury and their effects and attempts particularly to delineate the significance of dental amalgam as a factor in hypersensitivity reactions and in the human body burden of mercury. Dental personnel are evaluated as a potentially high-risk group for mercury exposure. Dental amalgam and alternative restorative materials are considered, the removal of amalgam being evaluated as a therapeutic modality. The “anti-amalgam” perspective is scrutinised and the validity of the claims assessed. A review of the scientific literature, and the statements of national and international dental and scientific literature, and the statements of national and international dental and scientific organisations reflect the general support for the safety of dental amalgam. There is no evidence that health risks are associated with the use of dental amalgam other than rare local allergic reactions and oral lichenoid lesions. Notwithstanding the usefulness and safety of dental amalgam certain recommendations and conclusions are made in respect of future approaches to the utilisation of this material and for mercury in general. Further objective scientific research is necessary to determine the effects on human health of chronic exposure to low levels of mercury. There is the need for accurate general population threshold levels to be established for mercury vapour with special consideration for the vulnerable members of the community. The health professions have a significant role to play in providing informed opinion and advice for their patients and the public, in countering the more eccentric claims of the anti-amalgamists and assuaging the anxiety and confusion which accompanies this subject.

In this thesis, I investigated curvilinear features on the surface of Mercury and the impact of illumination bias upon observations of those features. I also demonstrated their utility with regard to photostratigraphy and suggest areas where BepiColombo will provide beneficial additional data. Basin-edge scarps occur within volcanically-filled impact basins in all areas of the surface of Mercury. Many large impact basins are filled with Smooth Plains (volcanic) units. I hypothesise that fault nucleation occurs on the mechanically weak interface between the base of the volcanic fill units and the original floor of the impact basin. Using crater size-frequency distribution analysis I have established that resolvable deformation of basin-edge scarps ceased between 1.1 and 0.6 Ga. Based upon location and morphology, I concluded that catenae are likely to be formed by secondary impact ejecta. They are of use when establishing stratigraphic relationships between impact basins, since they extend further away from the primary basin than the ejecta blanket, and tend to remain observable for longer. The stratigraphic map of impact basins Aneirin, Sanai and the immediately surrounding areas demonstrated this, as – despite the basins being the same morphological class (C2) – catenae related to Aneirin were formed after the formation of Sanai. Aneirin is therefore the younger basin. Mercury’s near-zero obliquity means that curvilinear features aligned parallel with the illumination azimuth (east-west at low-mid latitudes) would be likely to be underrepresented in the global population. Using shaded-relief models with alternative artificial illumination to complete resurveys, I found that my global survey of basinedge scarps has been affected. Consequently, I advise the use of shaded-relief models in addition to imagery when mapping curvilinear features. I anticipate that the improved instrumentation of BepiColombo MPO will be invaluable when carrying out stratigraphic mapping and global surveys of specific features such as basin-edge scarps and catenae.

The thesis comprises four main chapters on chemical reactions and kinetics of some of the processes involved in the global mercury cycle. In the first chapter, the UVA irradiation of aqueous acidic mercuric chloride in the presence of large excess of Fe(III) organic diacid complexes results in partial reduction of the mercuric ion to elemental mercury. The pseudo-first-order rate constant (k) for photoreduction reaction is pH-dependent. Similar results were obtained using visible irradiation although the rates were ca. 10 times slower. The mechanism of photoreduction is inferred to involve reaction of Hg(II) with a secondary photoproduct, the strongly reducing radical anion CO 2-•. No other previous reports have suggested the involvement of this radical in mercury reduction. In the presence of dissolved oxygen, competition for CO2-• between Hg(II) and O2 reduces the rate and efficiency of mercuric ion reduction. The O2-•/HO2 products do not reduce Hg(II). On the contrary, their disproportionation leads to the formation of H2O2 which causes a slow reoxidation of Hg(0). In the second chapter, the reaction rate of UVA photoreduction of Hg(II) ions by fulvic and humic acids was found to have higher values in the pH range of 5 to 6 which is relevant to most aquatic environments, within this pH range, speciation calculations show that most of Hg(II) will bind to DOC. The effects of environmentally relevant parameters such as Hg(II)/HS ratio, and chloride concentration were investigated and the likely mechanism identified. The interaction of DOC with Hg species is not only limited to photoreactions but also the complexation reaction affects the bioavailability and speciation of Hg. This was the topic of the last two chapters. The kinetic stability of Hg-HS and McHg-HS complexes was characterized by different combined techniques; the competitive ligand exchange method (CLEM) combined with inductively coupled plasma-mass spectrometer (CLEM-ICP-MS) and the tangential flow ultrafiltration (TFUF) combined to CLEM-ICP-MS. The Hg-HS complexes can be described by at least two kinetically distinguished components; the more inert (slow) with a dissociation rate constant in the order of 10-5 s -1, and a labile component with a dissociation rate constant in the order of 10-3 s-1, protons (H+) was found to compete with Hg2+ for the strong binding sites, Hg/HS concentration ratio also was an important parameter, when [Hg 2+] was high then the strong binding sites was saturated and the excess Hg bound to the weak sites. (Abstract shortened by UMI.)

Le mercure est un composé toxique. En zone polaire, au printemps, une chimie extrêmement particulière est à l'origine, après oxydation, de son dépôt en surface du manteau neigeux. Ces phénomènes appelés « Atmospheric Mercury Depletion Events » (AMDEs) ou « pluies de mercure » sont à la base d'une contamination encore mal renseignée des écosystèmes polaires. Lors de campagnes de terrain en Arctique, nous avons observé sept AMDEs, et avons étudié les paramètres physico-chimiques susceptibles de gouverner l'apparition de ces événements. Le rôle des basses températures et l'implication des nuages glacés parmi les surfaces gelées actives sont évoqués. L'impact de ces AMDEs en terme de teneurs en mercure dans la neige de surface a également été examiné. Les dépôts résultant de ces phénomènes n'aboutissent pas forcément à une contamination marquée de la neige de surface, et nos connaissances sont aujourd'hui trop limitées pour pouvoir quantifier l'apport toxique des AMDEs sur l'Arctique.

Les deux premiers chapitres de la thèse présentent le principe d’un étalon de fréquence optique et les applications qui en découlent. Les principaux avantages métrologiques de l’horloge à réseau optique de mercure sont mis en avant, et quelques rappels théoriques d’interraction matière-rayonnement appliquée à la métrologie des fréquences sont effectués. Le montage expérimental est décrit de manière générale dans le chapitre 3, en insistant particulièrement sur les différentes sources laser utilisées. Les améliorations apportées au montage durant la thèse, font l’objet du chapitre 4. La première amélioration concerne le laser de refroidissement à 254nm. Mes travaux nous ont permis d’augmenter le temps d’interrogation des atomes, étape nécessaire pour une nouvelle mesure de stabilité de l’horloge et la caractérisation des effets systématiques. Afin d’augmenter ultérieurement la stabilité, une refonte de la cavité optique qui piège les atomes dans le réseau s’est révèlée indispensable. La nouvelle cavité permet de capturer 10 fois plus d’atomes grâce à une profondeur de piégage acrue d’un facteur 3, influant directement sur le rapport signal sur bruit. Enfin, les résultats expérimentaux obtenus sont décrits dans le 5ème et dernier chapitre. La spectroscopie sur fond noir d’un échantillon de mercure polarisé en spin avec une largeur de raie record de 3.3Hz nous a permis de mesurer une stabilité de 1.2x10 -15 à une seconde, soit presque un facteur 5 mieux par rapport à notre précédente mesure. Une caractérisation de plusieurs effets systématiques sur la transitions d’horloge (shift colisionnel, effet zeeman ou encore effet de la lumière de piégage) a été menée au niveau de 10-16
The first two chapters of thesis describe the basics of optical standards and its applications. Highlight advantages of mercury as a frequency reference in optical lattice clock and give theoretical background about atom-light interaction, origins of systematic shifts and their influence on stability of a clock. The third chapter describes the experimental setup. It includes the schemes and operation of the main laser systems and their characteristics, the vacuum chamber and magneto-optical trapping of atoms. The fourth chapter is about the setup improvements that I made during the thesis. It describes the new doubling stage at 254 nm for the cooling laser system that was designed and implemented during the thesis. The new doubling stage allowed us to perform spectroscopies with long integration times necessary for the measurement of stability of our clock and systematic shifts. The second major and important improvement was the change of the lattice trap cavity. The new lattice cavity allowed us to increase trap depth by a factor of 3, number of trapped atoms by 10, improved the signal to noise ratio and increased stability of the clock. The fifth chapter tells about the obtained results. Thanks to all the technical improvements spectroscopy of the clock transition with the record linewidth of 3.3 Hz was demonstrated. State selection and spectroscopy on dark background were implemented. Stability of the clock was improved by a factor of 5 and measured to be 1.2*10-15 at 1 s. No observable collision shift and second order Zeeman shift were measured at the uncertainty level of ~1*10-16. The shift of the clock frequency due to lattice light was measured to be below 6*10-17

The existence of immune self-tolerance allows the immune system to mount responses against infectious agents, but not against self-molecular constitutes. Although self-tolerance is a robust phenomenon, in some individuals as well as in experimental models, the self-tolerance breaks down and as a result, a self-destructive autoimmune disease emerges. The underlying mechanisms for the development of autoimmune diseases are not known, but genetic, environmental and immunological factors are suggested to be involved. In this thesis, we used murine mercury-induced autoimmunity to test this suggestion.

In susceptible mice mercuric chloride induces a systemic autoimmune disease characterized by increased serum levels of IgG1 and IgE, production of anti-nucleolar autoantibodies (ANolA) and formation of renal IgG deposits. In contrast, in resistant DBA/2 (H-2^d) mice, none of these characteristics develop after exposure to mercury. By crossing and backcrossing mercury-resistant DBA/2 mice to mercury susceptible strains, we found that the resistance was inherited as a dominant trait in F1 hybrids and that one gene or a cluster of genes located in the H-2 loci determined the resistance to ANolA production, whereas resistance to the other characteristics was found to be controlled by two or three non-H-2 genes.

We further put forward the “cryptic peptide hypothesis” to investigate whether mercury and another xenobiotic metal use similar pathway(s) to induce the H-2 linked production of ANolA. We found that while mercury stimulated ANolA synthesis in all H-2 susceptible (H-2^s, H-2^q and H-2^f) mouse strains, silver induced only ANolA responses in H-2^s and H-2^q mice, but not in H-2^f mice. Further studies showed that the resistance to silver-induced ANolA production in H-2^f mice was inherited as a dominant trait.

We next tested the proposition that mercury induces more adverse immunological effects in mouse strains, which are genetically prone to develop autoimmune diseases, using tight-skin 1 mice, an animal model for human Scleroderma. It was found that in this strain, mercury induced a strong immune activation with autoimmune characteristics, but did not accelerate the development of dermal fibrosis, a characteristic in Tsk/1 mice.

Finally we addressed the Th1/Th2 cross-regulation paradigm by examining if a Th1-type of response could interact with a Th2-type of response if simultaneous induced in susceptible mice. Our findings demonstrated that mercury-induced autoimmunity (Th2-type) and collagen-induced arthritis (CIA) (Th1-type) can interact in a synergistic, antagonistic or additive fashion, depending on at which stage of CIA mercury is administered.

Mercury amalgam microelectrodes, typically fabricated by electrodeposition of mercury onto metal (platinum, gold, silver) inlaid disks, possess certain advantageous properties for scanning electrochemical microscopy (SECM) and electroanalysis. But as applications require more and more precision, fundamental questions concerning the exact shape and constitution of the amalgam can become important for interpreting SECM experimental data. The purpose of this study is to analyze in depth the formation of the amalgam, in order to provide a better understanding of the key physical processes, and so be able to judge of the accuracy of the currently used models and refine them when necessary. The amalgam formation is the result of several processes that occur roughly at two different scales: the global scale, which is microscopic, and the local scale, of the order of few nanometers. On the global scale, the dominant physical process is the mass transport, driven almost entirely by diffusion, which determines the rate of mercury deposition. Other phenomena occur at the smaller local scale. Their understanding is essential to predict precisely the volume and shape of the amalgam at shorter times. Among these local phenomena, nucleation and droplet interactions appear critical. The former sets the formation rate and the size of the isolated mercury droplets that are initially formed at the surface of the electrode. An understanding of the latter is necessary to determine the droplet coalescence process. Among the specific accomplishments of this Master thesis work, a time scale analysis of the global phenomena has been performed leading to the conclusion that quasi-steady state diffusion of mercury ions in the bulk mainly defines the electrodeposition rate. Then, a series of analytical formulations for diffusion-limited electrodeposition current available in the literature has been quickly analyzed, leading to development of analytical/numerical models. These latter have been implemented, and results were critically compared with experimental data, leading to the conclusion that the early electrodeposition was not enough finely modeled. Mercury droplets nucleation and surface interaction have been identified as relevant processes of this period. They have next been investigated in detail, leading to the characterization of the nucleation process, and the derivation of two complimentary approaches on charged droplet stability. Regime maps have been developed, providing first explanations and quantitative information on charged droplet stability dependence on potential applied, electrolyte and droplet size. Finally, through analysis of theoretical predictions, a series of electroanalytical experiments have been proposed for the future validation of the suggested theoretical models.

Mercury is commonly present with gold in nature. As a result it has a tendency to follow gold through the cyanide recovery circuit and ends up in the electro-winning cell as elemental mercury. The laws on the sale and international transport of this mercury are changing. Ultimately, it appears that it will be necessary to stabilize and dispose in a stable form. Mercury sulfide (HgS) and mercury selenide (HgSe) have significantly lower solubilities. The concept of using a thiosulfate dissolution/precipitation method to stabilize mercury as mercury sulfide has been investigated. Comparing the solubilities of mercury sulfide and mercury selenide, mercury selenide is much less soluble. For this reason, the second idea in this thesis is to use sodium thioselenate as a source of selenium in mercury solution to produce mercury selenide. To pursue this project, mercury analysis, mercury leaching and mercury precipitation tests were performed at different temperatures and solution conditions. The resulting solutions were analyzed by Atomic Absorption Spectroscopy (AAS) and the solid precipitates were analyzed by X-ray Diffraction. The EDTA titration method for mercury analysis is effective for a simple mercury nitrate solution. If sodium thiosulfate was added in the solution, thiosulfate interfered with the solution and the titration method was not effective. As a result the AAS method was adopted. Red mercury sulfide can be precipitated by simple aging of mercury thiosulfate solution. Parameters such as temperature, pH and thiosulfate concentration have an effect on the rate and extent of mercury sulfide precipitation. With an increase of temperature, thiosulfate concentration and at lower pH, the mercury precipitation rate increases. However at very high temperature such as 70ºC and 80ºC mercury precipitates as a mixture of red and black mercury sulfide. Thioselenate synthesis was attempted from a mixture of sodium sulfite and selenium powder. The reaction between sulfite and elemental selenium was too slow to be useful. The environmental stability of the mercury sulfide precipitates produced from thiosulfate solutions was investigated. Solid Waste Disposal Characterization (SWDC) tests were done to check the precipitation limit for land disposal and Resource Conservation and Recovery Act (RCRA).

Mercury is often found associated with gold and silver minerals in ore bodies. It is recovered as liquid elemental mercury in several stages including carbon adsorption, carbon elution, electrowinning and retorting. Thus a great amount of mercury is produced as a by-product in gold mines. The Mercury Export Ban Act of 2008 prohibits conveying, selling and distributing elemental mercury by federal agencies in United States. It also bans the export of elemental mercury starting January 1, 2013. As a result, a long-term mercury management plan is required by gold mining companies that generate liquid mercury as a by-product. This thesis will develop a process to effectively convert elemental mercury into much more stable mercury sulfide and mercury selenide for safe disposal. The process consists of 1) extraction of elemental mercury into solution to form aqueous mercury (II) and 2) mercury precipitation as mercury sulfide or mercury selenide. Elemental mercury can be effectively extracted by using hypochlorite solution in acidic environment to form aqueous mercury (II) chloride. The effect of different parameters on the extent and rate of mercury extraction were studied, such as pH, temperature, stirring speed and hypochlorite concentration. Results show that near complete extraction can be achieved within 8 hours by using excess sodium hypochlorite at pH 4 with a fast stirring speed of 1000RPM. Mercury precipitation was achieved by using thiosulfate and selenosulfate solution. In thiosulfate precipitation, cinnabar, metacinnabar or a mixture of both can be obtained depending on the experimental conditions. Elevated temperatures, acidic environment and high reagent concentrations favour the precipitation reaction. Complete mercury removal can be achieved within 4 hours. However, it appears that the less stable metacinnabar tends to form when the precipitation rate increases. Selenosulfate solution can be produced by dissolving elemental selenium in sulfite solution at elevated temperature. Precipitation of mercury selenide using selenosulfate reagent was found to be very effective. The precipitation rate proved to be extremely fast, and the formed precipitates have been confirmed to be tiemannite (HgSe) in all experiments. Finally, Solid Waste Disposal Characterization (SWDC) experiments were conducted to examine the mobility of the formed mercury sulfide and mercury selenide. The results show that none of the formed precipitates exceed the Ultimate Treatment Standard (UTS) limit.

This research focuses on the development, evaluation, and application of a mercury (Hg) mass balance model for predicting the accumulation of Hg in fish. This model requires accurate estimates of Hg elimination rate by fish and feeding rates to adequately predict Hg concentration in fish. An empirical model was developed to estimate Hg elimination by fish using data obtained from published experiments. This analysis showed that Hg elimination rate was overestimated in short-term experiments, positively correlated to water temperature, negatively correlated to body size, and that the elimination rate of inorganic Hg was faster than that of methylmercury. This empirical model was then incorporated in a Hg mass balance model to predict the concentration of Hg in fish. The Hg mass balance model accurately predicted Hg concentration in fish when it was combined with food consumption rates that were determined using a radioisotopic method. This analysis suggested that the parameters of the Hg mass balance model were adequate for predicting Hg concentration in fish. I also showed that Hg concentration tended to be underestimated by the Hg mass balance model when it was combined with feeding rates determined with a laboratory-derived bioenergetic model, probably because activity costs derived in the laboratory do not reflect activity costs of fish in the field. Beside predicting Hg concentration in fish, I showed that this mass balance model could also be used to estimate feeding rates of fish in the field by measuring the concentration of Hg in fish. This approach was validated using data obtained from a published experiment. It was also successfully tested using independent estimates of feeding rates obtained with a radioisotopic method. I applied this Hg mass balance model to compare the energy budget of sympatric populations of dwarf and normal whitefish (Coregonus clupeaformis). This analysis showed that dwarf whitefish consumed 40--50% more food than normal whitefi

The mass flow event resulting from the 1996 flood in the Saguenay region buried the mercury-contaminated indigenous sediments at the head of the Saguenay Fjord under up to 50 cm of postglacial deltaic sediments. This study investigated whether this deposit served as an efficient geochemical barrier to the remobilization of mercury and its availability to the benthic organisms. The vertical distributions of total mercury and methyl mercury (MeHg) in the sediments and pore waters were measured in box cores recovered at three stations along the main axis of the Saguenay Fjord and in the Baie des Ha!Ha!, in successive years between 1996 and 2002. The total solid mercury profile time-series shows that most of the mercury remobilized from the contaminated, indigenous sediments was trapped below or slightly above the former sediment-water interface. Strong correlations with acid-volatile sulphide profiles and extractions of pyrite-associated mercury indicate that most of this mercury was co-precipitated with authigenic iron sulphides. The mercury that was not sequestered by iron sulphides, diffused into the flood layer where it was scavenged by organic matter or methylated. Mercury sequestration at SAG-05 occurred within the older indigenous sediments, in contrast to SAG-09 where it occurred at or above the original sediment-water interface. The sediments are richer in organic matter, more reducing and, thus, establishment of suboxic conditions and precipitation of authigenic iron sulphides occurred more rapidly. The abundance of mercury at the former sediment-water interface and the low dissolved SigmaH2S concentrations, buffered by acid-volatile sulphide precipitation, both favored mercury methylation. A strong correlation between the distribution of acid-volatile sulphides and methyl mercury in the sediment also reveal that the former may serve as a sink for the latter. Throughout the sediment cores, sediment-water partitioning of MeHg as well as Hg(II) is controlled in great part by the residual organic matter content of the sediment.

Two large, nationwide monitoring data sets were compiled and statistically treated in order to create a national picture of the problems with high contents of mercury (Hg) and radiocesium (137Cs) in fish. Beside these two data sets, 75 lakes in four counties (Västernorrland, Gävleborg, Örebro and Kronoberg) were studied in connection to an evaluation of different measures to decrease the content of Hg and 137Cs in fish. An important objective was to investigate and determine the relationship between the content in fish and the load of the elements and how this relationship was affected by different abiotic lake characteristics. Several alternatives to measure the lake doses of Hg and 137Cs were evaluated (concentration in different fractions in lake water, in settling particles, and in surface sediments). About 10000 Swedish lakes were calculated to have a mean Hg content in 1-kg pike (FHg) above 1 mg kg-1 (wet weight) in the end of 1980’s, that is a 5-fold increase compared to the calculated preindustrial mean value. The cumulated domestic Hg- sources of emission make the largest contribution to the presently high mercury levels in pike and particularly so in central and northern Sweden.The second most important cause is acidification and thirdly Hg emissions from European sources. The content of 137Cs in fish normalized to 100 g perch (FCs) was above the limit for commercial sale, 1500 Bq kg-k in about 14000 Swedish lakes during autumn of 1987. An empirical model including Chernobyl fallout, hydraulic residence time and ionic strength explained almost 60 % of the inter-lake variation in FCs. At the same level of fallout, this difference in lake sensitivity, gave a tenfold difference in the initial transfer from fallout to small perch. A significant relationship was demonstrated between the lake dose of 137Cs and the content in fish. No such clear relationship existed for Hg due to the much more complex chemical and biological behaviour of Hg, where especially factors affecting méhylation and food web structure seems crucial. Lakes with a low relative sedimentation of Hg did also have a low relative sedimentation of 137Cs due to differences in particle sedimentation rates between the lakes. The sedimentation rate of radiocesium was well correlated to the natural concentration of major base cations and intercorrelated parameters such as pH, alkalinity and conductivity. The higher scavenging capacity in lakes with higher concentration of major base cations was due to higher particle sedimentation rates and higher K<i values in these lakes. However, the water chemistry was probably not causal in this respect, despite the high correlation, the distribution and sedimentation coefficients for radiocesium was not notably affected of the increased mean concentration of major base cations after liming and potash addition. It is suggested that a likely causal factor rather would be the amount and nature of scavenging agents (possibly clay minerals), which in these lakes was indicated by the natural concentration of base cations in the water. In general, the remedial measures gave the intended water chemical response with substantially increased mean values of alkalinity, hardness and pH. Two years after the start of the remedies, the Hg concentration in small perch (Hg-pe) was reduced by about 30% on average. The sedimentation rate of Hg decreased during 1988 and 1989 (i.e. after remedial measures) in contrast to the mean concentration of total Hg in water, thus, the retention decreased. None of the methods applied gave any rapid and clear reduction in the concentrations of 137Cs in fish, in comparison with lakes where the water chemical or biological conditions not were changed.

Diss. (sammanfattning) Umeå : Umeå universitet, 1993,, härtill 6 uppsatser.

digitalisering@umu.se

The presence of ultra-trace levels of mercury in industrial gas and condensate streams is a cause of both environmental and production concern. The toxic nature of the element, in all forms, together with its ability to shut-down large processing plants dictates a need for its accurate and precise measurement. The study which investigated the recovery of various mercury species, spiked into synthetic and real condensate samples using conventional and new digestion and/or extraction techniques showed recovery was dependent upon the speciation. Using the most efficient technique, L-cysteine with persulphate, recoveries of over 90 % were obtained for diphenyl mercury, ethyl and phenyl mercury chlorides and mercury chloride. The recovery of 15% for the important dimethyl mercury species limits the use of this technique. A novel technique has been developed for the determination of total mercury in complex liquid hydrocarbons. Samples (up to 1.0 ml) were vaporised (400°C) and swept through a gold-coated silica trap maintained at 200°C, which retained all mercury species and discarded the matrix. The trap when heated to 900°C released the mercury for measurement by atomic fluorescence spectrometry (AFS). The recoveries for eight mercury species spiked (10 to 50 ng ml -1) into toluene and condensate were generally over 90 %. The instrumental limit of detection (LOD) was 11 pg. The total mercury content of gas condensates, gasolines and heavy oils were determined. Gas chromatography coupled, via a pyrolysis interface, with AF detection was able to determine mercury species in gas condensate, at picogram levels (LOD: 2.5 to 7 pg) using a direct sample injection procedure. For a given column system the positive identification and quantification of up to eight mercury species was obtained. A maximum injector temperature of 125 °C was recommended, to avoid the conversion of species. Mass balance calculations show a strong correlation between the total mercury content and the sum of the lower diallcyl mercury species, for all condensate samples studied. Three commercially available mercury removal systems, A, B and C produced a reduction in the mercury content of hydrocarbon streams under pilot plant conditions. The two stage system, 'A', produced a minimum of 30 % conversion from organomercury to elemental mercury after the hydrogenation reaction in stage 1. While elemental mercury was adsorbed by the stage 2 reactor, the organomercury species were not removed. The single stage adsorber 'B' showed 100 % removal efficiency for three dialkyl mercury species in liquid hydrocarbon streams. The removal efficiency for adsorber 'C' was species dependent. Two common condensate species gave values of 50 to 80 % removal efficiency while the third species showed time-dependent bleed-off.

Microbiology and Immunology
Ph.D.
Etiological agents causing autoimmune diseases largely remain unknown. However, several lines of evidence suggest that environmental factors such as heavy metals (arsenic, lead and mercury) play a crucial role in the development of autoimmune disorders. In our model of mercury-induced autoimmunity, administration of subtoxic doses of HgCl2 to genetically susceptible strains of mice result in an autoimmune disease characterized by the production of highly specific anti-nucleolar autoantibodies, hypergammaglobulinemia and nephritis. However, mice can be tolerized to the disease by a single low dose administration of HgCl2 (tolerogenic dose). Previous studies from our lab had demonstrated that CD4+ CD25+ Foxp3+ regulatory T cells (Tregs) control the induction and maintenance of tolerance to mercury. We investigated the therapeutic role of Tregs in our model by utilizing agents that are known to stimulate in vivo expansion of Tregs. We studied two such agents, CD3-specific non-Fc receptor-binding [(Fab’)2 fragment] monoclonal antibody (Anti-CD3) and immune complexes containing recombinant IL-2 and anti-IL-2 monoclonal antibody (IC). In our model, treatment of mice with Anti-CD3 had no effect on Treg population. Administration of Anti-CD3 with the tolerogenic dose prevented induction of tolerance and failed to improve the maintenance period of tolerance. Anti-CD3 in presence of mercury activated the immune-system causing splenomegaly and expansion of B cell population. Overall, in contrast to its protective role in other experimental autoimmune disease models, Anti-CD3 exacerbated mercury-induced autoimmune syndrome. Treatment of mice with IC resulted in selective expansion of Tregs with a modest decrease in IgE levels and autoantibody production. Administration of IC with the tolerogenic dose led to a reduction in autoantibody response, thus IC was able to extend the maintenance period of tolerance to mercury. Lymphocyte Activation Gene-3 (LAG-3) is an inhibitory molecule that maintains lymphocyte homeostatic balance by controlling effector T cell expansion and contributing to the suppressive functions of Tregs. Thus, with the goal to understand the impact of homeostatic balance on Hg-induced autoimmunity, we investigated the role of LAG-3 in our model. Administration of an anti-LAG-3 monoclonal antibody broke tolerance to Hg resulting in autoantibody production and an increase in levels of serum IgE. Additionally, LAG-3-deficient B6.SJL mice exhibited an increased susceptibility to mercury-induced autoimmunity whereas, wild type controls suffered only from a mild disease. Moreover, adoptive transfer of wild-type CD4+ T cells protected LAG-3-deficient mice from mercury-induced autoimmunity. Therefore, we conclude that LAG-3 exerts an important regulatory effect on autoimmunity elicited by a common environmental pollutant.
Temple University--Theses

A mathematical model of mercury resistance was designed which describes the following reactions: the cellular uptake and volatilisation of Hg2+, binding of the DNA by the regulator, mer protein synthesis, and dilution of quantities by cell growth. A total of 66 biological experiments were then selected from the scientific literature from studies of Tn21 and Tn501 in E. coli at 37 °C. These experiments were repeated in the computer simulation and the information from their 489 data points was incorporated into the 16 parameters of the model using the Metropolis-Hastings algorithm. This model is very useful biology for four reasons. Firstly, it shows whether the data from existing biological experiments are consistent with each other or not. Secondly, it predicts the previously unknown concentrations of mer proteins in cells of each mercury phenotype. In addition, it challenges the hypotheses that the rates of uptake and volatilisation are always equal in resistant cells and that the plasmid copy number effects replicated by the model are caused by the saturation of MerT in the membrane. Thirdly, the model can guide the design of future experiments. This guidance can minimise the use of laboratory resources and will ensure that sufficient data are created for every parameter in the model under standardised conditions. Finally, the modelling has identified many areas for future biological research: the absolute concentrations of mer proteins, the significance of MerC and MerD, plasmid copy number effects and substrate inhibition, the three uptake processes (non-mer import, MerA transport, and non-MerA transport), the order of DNA + MerR + Hg2+ binding, the nature of toxicity, and the concentrations of mercury in each of the five cellular binding sites.