The mobility of arsenic is controlled by the mineral source of arsenic and a host of biogeochemical factors such as pH, oxidation-reduction reactions, precipitation-dissolution reactions, adsorption-desorption processes, and the activity of microorganisms. In this study, sequential extraction and microscopic methods were used to evaluate arsenic partitioning in different phases in sediments and host rock at the Brinton arsenic mine (BAM) site. Results demonstrate spatial variability of arsenic in sediments, although the partitioning of arsenic in different phases was similar in both mine tailing and stream channel sediments. The sequential extraction results demonstrate that between 60 and 80 % of the total arsenic in sediments is associated with iron oxides, and an additional phosphate extraction showed that the majority (80%) of arsenic associated with the oxides is adsorbed. Imaging and analysis by scanning electron microscopy (SEM) and electron microprobe analysis (EMPA) show the presence of three arsenic bearing minerals, arsenopyrite, scorodite and arsenic-rich iron oxides, in both sediment and the host rock. In sediment, the minerals are present as individual grains, but in the host rock, they are present together, often with arsenopyrite at the core, surrounded by scorodite and/or elemental sulfur, which is rimmed by iron oxides. This spatial arrangement illustrates two weathering patterns of arsenopyrite, one that involves oxidation to form scorodite, which further dissolves to form arsenic-rich iron oxides; in this weathering series, sulfur presumably forms dissolved species which migrate away from the mineral. Another pattern, observed in several samples of host rock, involves formation of elemental sulfur in addition to scorodite and iron oxides. Results of this study have implications for arsenic mobility at the Brinton site and other mine sites where arsenic minerals are present. Although arsenopyrite is the main ore mineral, the main reservoir of arsenic in sediments is iron oxides. However, in the end it is the biogeochemical mechanism that releases arsenic from the mineral that will control arsenic mobility. In the case of iron oxides, desorption or reductive dissolution will promote arsenic release, whereas oxidizing conditions are required for arsenopyrite to release arsenic. / Master of Science

A new regulation has been proposed that would lower the acceptable level of arsenic in drinking water from the current standard of 50 ppb. Therefore, research into effective arsenic removal treatment is important, especially for hard to treat waters with high concentrations of silica. The first phase of research was designed to determine if sand ballasted coagulation is a viable means of removing arsenic from drinking water, and if so, to identify the water qualities in which the technology performs best. A jar test protocol was developed and tested on a wide range of waters to compare microsand ballasted coagulation and other coagulation based treatment processes in terms of arsenic removal. Secondary impacts of the microsand process such as residual turbidity, iron, post-treatment membrane filter run length, and TOC removal were also considered as part of this evaluation. Microsand ballasted coagulation provided promising results for many of the simulated groundwater test conditions in which more than 80% of the arsenic regulation costs will be incurred. However, like conventional coagulation/sedimentation, microsand ballasted coagulation performed poorly in waters with high silica and high pH. Thereafter, a second phase of research more closely examined the kinetic behavior of arsenic sorption to amorphous and granular oxides in the presence of silica and calcium. At pH 8.5, calcium dramatically improved arsenic sorption to amorphous iron hydroxide in the presence of silica over short reaction times, but had no long-term advantage. This result could have considerable applications for treatment in that it suggests water quality controls the required reaction times. Additionally, batch tests indicated that activated alumina granular media was more sensitive to water quality than granular ferric hydroxide; however, calcium eliminated silica interference to arsenic sorption onto activated alumina. / Master of Science

Arsenic is a naturally occurring element, which is toxic to aquatic biota especially in disturbed areas where it may be found at high concentrations. A headwater stream adjacent to an 85 year-old abandoned arsenic mine was investigated to determine the influence of arsenic on stream biota and processes using an upstream (reference) and downstream (mine-influenced) comparative approach. Arsenic concentration was measured monthly at 10 sites along the stream length. Benthic macroinvertebrate surveys were conducted in both reaches five times throughout the course of a year. Leaf breakdown assays were conducted in reference and mine-influenced reaches. Leaf biofilm respiration was recorded during leaf breakdown assays and also with experimental arsenic additions to reference reach leaf biofilms. At the field site, arsenic concentrations varied from below detection limit (<2.5µg/L) to more than 12 mg/L. Macroinvertebrate density was greatly reduced down-gradient of the mine with 154 individuals/m2, while upstream there were 7869 individuals/m2. Leaf biofilm respiration rates were comparable to others found in the literature and not significantly different between reference and mine-influenced reaches. Further, experimental additions of arsenic did not alter biofilm respiration under laboratory conditions. However, shredder abundance on leaf packs was eight to twenty times greater upstream than the mine-influenced reach. Leaf breakdown rate varied two to three fold among sites distributed above and below the mine and were significantly lower in reaches of elevated arsenic concentration. Together, these data suggest that the mining operations on this headwater stream have altered organic matter processing primarily by decreasing invertebrate densities and limiting shredder abundance. / Master of Science

Ensuring the safety of drinking water, treating wastewater, and remediating soil are ongoing global concerns. Adsorption is a favorable substitute for traditional methods including coagulation, precipitation, membrane separation, and ion-exchange in water purification. Biochar-based sorbents are cheap and effective due to high density surface functional groups, which can retain a wide range of chemicals. This dissertation focused on three main projects involving magnetite (Fe3O4) and struvite/struvite-K (MgNH4PO4.6H2O/MgKPO4.6H2O) deposited high surface area Douglas fir biochar (DFBC) based engineered material for water and soil remediation. Chapter II focuses on toxic arsenic (V) contaminated wastewater remediation using magnetite particles dispersed Douglas fir biochar. This chapter highlights the effect of pH, adsorption kinetics, isotherms, particle sizes, ionic strength, the impact of competitive ions and fixed-bed column sorption on As(V) removal and redox transformation of As(III) to As(V) during the adsorption in a wide range of pHs. Moreover, Mössbauer spectroscopy was used to analyze the composition of Fe3O4 particles formed on Fe3O4/DFBC. Furthermore, X-ray photoelectron spectroscopy studies were conducted to study As(V) adsorption onto Fe3O4/DFBC at a wide range of solution pHs to verify the predominant As adsorption mechanisms. Chapter III focuses on challenging per- and poly-fluoroalkyl substances (PFAS) contaminated water remediation at low concentrations using Fe3O4/DFBC. In this work, we used classical adsorption techniques to purify PFAS contaminated water. Chapter IV is focused on remediation of depleted soil using struvite/struvite-K- modified Douglas fir biochar (BCF). In this study, we examined the leaching rates of PO43-, NH4+, K+, and Mg2+ from BCF in different water matrices, different temperatures, and a wide range of pHs. Greenhouse experiments were conducted to evaluate the performances of BCF.

Arsenic (As) in drinking water poses a critical threat to public health. More than 150 million people worldwide are at risk of developing diseases from unsafe concentrations of As in groundwater. Arsenic occurs naturally in rocks, soils, and sediments and generally remains associated with solid phases. However, changes in aquifer geochemistry can mobilize As into groundwater, contaminating drinking water sources. This dissertation investigates As cycling in an aquifer contaminated by petroleum hydrocarbons near Bemidji, Minnesota, where As is mobilized into groundwater due to biodegradation of hydrocarbons coupled to reduction of ferric oxides. The first project describes how aquifer sediments act as both sources and sinks for As in groundwater, depending on the prevailing redox conditions. Results show that As is released to groundwater near the hydrocarbon source but is removed near the hydrocarbon plume's leading edge. Comparison of data from 1993 to 2016 shows that As has been redistributed in aquifer sediment as the plume has expanded over time. The second project presents a mass balance for As, which shows that despite elevated As in groundwater (up to 230 μg/L), >99.7% of As mass in the aquifer is in sediments. Calculations demonstrate that As in sediment can be 22x less than the method detection limit and still cause unsafe concentrations in groundwater, suggesting that the use of standard methods limits our ability to predict where naturally occurring As poses a threat to groundwater. In the third project, a reactive transport model simulates As cycling for 400 years. Results show that sorption of As to ferrihydrite limits As transport within 300 m of the hydrocarbon source. Modeling predicts that over the plume's lifespan, more groundwater will be contaminated by As than benzene, the primary contaminant of concern in hydrocarbon plumes. Combined, these studies suggest that many aquifers are vulnerable to unsafe As concentrations due to mobilization of natural As if bioavailable organic carbon is introduced. Although aquifers can attenuate As, it may take centuries for As to be fully removed from groundwater, suggesting it is prudent to account for natural contaminants like As when developing remediation strategies at petroleum spill sites. / Ph. D. / Arsenic (As) in groundwater used for drinking water is a risk to public health. More than 150 million people worldwide are at risk of developing diseases and cancer from unsafe levels of As in groundwater. Arsenic occurs naturally in rocks, soils, and sediments. However, changes in aquifer chemistry can release As from these solid materials into groundwater, contaminating drinking water sources. This dissertation investigates As cycling in a petroleum-contaminated aquifer near Bemidji, Minnesota, where As is released into groundwater due to the breakdown of petroleum by microorganisms under zero-oxygen conditions. The first project describes how sediments release As to, and remove As from, groundwater. Results show that As in groundwater is removed by sediments under medium-to-high-oxygen conditions. Analyses of sediment collected in 1993 showed that in the past, similar processes affecting As in groundwater were occurring closer to the petroleum release site. Over time, the zero-oxygen conditions that allow As to be released into groundwater spread, causing a more widespread As release. The second project presents a mass balance for As, which shows that despite high As in groundwater (up to 230 μg/L), >99.7% of As is associated with sediments. Calculations demonstrate that the analytical methods used to detect As in sediment are not sensitive enough to predict where natural As poses a threat to groundwater. In the third project, a numerical model shows that the presence of iron oxide minerals limit As transport in groundwater. Modeling simulations suggest that in the future, more groundwater will be contaminated by As than benzene, the primary contaminant of concern in petroleum plumes. Combined, these studies suggest that many aquifers are vulnerable to the release of unsafe levels of As from naturally occurring sources if organic carbon is introduced. Although aquifers can naturally remove As from groundwater, it may take centuries for As to be fully removed, suggesting it is prudent to account for natural contaminants like As when developing clean-up plans at oil spill sites.

No description available.

M.Sc. (Geology) / Most rural communities in developing countries rely on borehole water as their only source of water. Since borehole water comes from underground, it is often considered pure and clean, but this is frequently not the case. Groundwater contains certain amounts of trace elements that may become deleterious to human health. The objectives of this investigation were to assess the concentration levels of Potential Harmful Trace Elements (PHTEs) and their spatial distribution patterns in borehole water in the Greater Giyani area of Limpopo, South Africa, and the potential human health risks associated with this. The method of research comprised two phases: (I) In the first phase, I assessed the occurrence and distribution patterns of PHTEs in the boreholes of the Giyani area. A total of 29 water samples were collected from boreholes (including 15 community boreholes and 14 primary school boreholes) in the Greater Giyani area during the dry season (July/August 2012), and for comparison another 27 samples (including 15 community boreholes and 12 schools boreholes) from the same localities during the wet season (March 2013). The samples were analysed for the trace elements arsenic (As), cadmium (Cd), chromium (Cr), selenium (Se) and lead (Pb) using the Inductively Coupled Plasma Mass-Spectrometry (ICPMS) technique. In order to assess the groundwater quality, PHTEs concentrations were compared with the South African National Standard of Drinking water (SANS 241-1:2011). (II) In the second phase, I evaluated the geographic variation between PHTEs and associated human health effects. This involved acquisition of data on a total of 100 cancer cases recorded during the period 2011-2014 at Nkhensani Hospital. ArcGIS Spatial analyst tool was used to create thematic maps illustrating spatial distribution of clinical data and arsenic concentrations in boreholes.

L'aquifère Tumbaco – Cumbayá, sujet de la présente étude, se situe dans le contexte typique des aquifères volcano-sédimentaires. Cet aquifère se localise dans la Vallée Interandine, à 15 Km à l'Est de Quito. L'aquifère principal est la formation volcano-sédimentaire Chiche. Il est limité par la rivière Chiche et San Pedro, la faille de Quito et le volcan Pasochoa. Le volcan Ilaló se trouve au milieu de la zone d'étude. Il forme un second aquifère essentiellement volcanique soumis à un géothermalisme lié au volcan, dont la partie enterrée du cône est apparemment au-dessous de la formation Chiche. La couche géologique en surface est appelée Cangahua. Elle recouvre toute la zone et elle est imperméable. L'exploitation des aquifères Chiche et Ilaló a été théoriquement suspendue à partir de 2006, quand des teneurs en arsenic supérieures à la norme de 10 microg/l ont été détectées. Notre objectif est d'améliorer la connaissance du fonctionnement intégral de ce système aquifère en utilisant trois axes principaux de recherche : i) l'hydrodynamique, ii) la géochimie et, iii) les isotopes stables, 18O et 2H, et radioactifs, 3H et 14C.L'hydrodynamique montre que le système aquifère a une saisonnalité très faible. Par ailleurs, les aquifères sont actuellement exploités par un usage industriel et domestique, contrairement à ce qui a été pensé au début. Le volcan sépare les parties Sud et Nord de l'aquifère Chiche et il fonctionne comme une barrière hydraulique du flux. Les rivières Chiche et San Pedro sont des axes de drainage de l'aquifère, au Nord et au Sud.L'analyse des paramètres physiques de l'eau ont mis en évidence deux aquifères bien différenciés : l'aquifère Chiche avec des CE et des températures plus basses que l'aquifère Ilaló. La chimie des ions majeurs a révélé un faciès de l'eau qui évolue d'un pôle Mg-HCO3 à un pôle Na-HCO3, dans l'aquifère Chiche et aussi dans l'aquifère Ilaló, alors que l'aquifère Chiche Sud est plus Mg-HCO3. Les teneurs en As sont plus élevées dans l'aquifère Ilaló que dans l'aquifère Chiche, où les teneurs baissent au fur et à mesure que l'on s'éloigne du volcan. Cet élément est d'origine naturelle, mais aucune corrélation significative n'a pas été trouvée pour l'aquifère Chiche. Cependant, dans l'aquifère Ilaló, une corrélation de 57% a été trouvée avec le fer, suggérant une interaction avec les oxydes de fer de la formation géologique.L'isotope radioactif 3H n'a pas été détecté dans l'eau des aquifères, à exception d'une source au Nord de la zone d'étude, dans la formation Chiche. Cette infiltration probable d'eaux récentes a été confirmée par le 14C, qui a des teneurs supérieures à 100%. Le reste des points de l'aquifère Chiche ont des activités 14C entre 45,4 et 87,4 pmc. Pour l'aquifère Ilaló les activités 14C sont < 20 pmc. L'âge de l'eau a été calculé et corrigée à partir du 13C qui montrait une contamination par le CO2 profond, qui donne des âges plus anciens qu'en réalité. Malgré la correction, les âges de l'eau continuent à se montrer très élevés, pour Chiche entre 400 et 4000 ans et Ilaló entre 11000 et 44000 ans. Les isotopes stables ont été utilisés pour identifier les zones de recharge. L'eau de l'aquifère Chiche a montré un comportement isotopique en 18O et 2H sous la droite météorique locale, avec une pente de 3,5, signal d'un fractionnement isotopique d'échange avec la roche chaude qui n'a pas été observé dans l'aquifère Ilaló. Le calcul de l'altitude de recharge a montré que l'aquifère Chiche s'alimente au pied du volcan Ilaló au Nord et au pied du volcan Pasochoa au Sud, en considérant des conditions climatiques similaires aux conditions actuelles. Pour l'aquifère Ilaló, la zone de recharge se trouverait sur les flancs du volcan, en supposant des conditions climatiques de recharge plus froides que les conditions actuelles. Mais cette zone ne serait plus fonctionnelle dû au dépôt de Cangahua.Les résultats suggèrent que les eaux de l'Ilaló se mélangent avec l'aquifère Chiche. / The Tumbaco – Cumbayá aquifer is found in the context of volcano-sedimentary aquifers. This aquifer is located in the Interandean Valley, 15 km to the east of Quito. The principal aquifer is the volcano-sedimentary formation Chiche. It is limited by the Chiche and San Pedro rivers, the Quito fault and the Pasochoa volcano. The Ilaló volcano is in the middle of the study zone and constitutes a second essentially volcanic aquifer, and is therefore subject to geothermal influences. This volcanic formation appears to be below the Chiche formation. The geologic layer on the surface is called Cangahua, it covers the entire zone and is impermeable. The exploitation of the Chiche and Ilaló aquifers was theoretically suspended in 2006, when arsenic concentrations > the WHO standard of 10 microg/l were found. Our objective is to improve the knowledge of the functioning of this aquifer system using three main research methods: i) hydrodynamics, ii) geochemistry and iii) stable isotopes, 18O - 2H, and radioactive isotopes, 3H - 14C.Hydrodynamics showed that the aquifer system has a low seasonality. We revealed that the aquifers are currently exploited for industrial and domestic uses, contrary to what was known at the beginning. The Ilaló volcano divides the south and north parts of the Chiche aquifer, with the volcano apparently acting as a hydraulic barrier for flows. The Chiche and San Pedro rivers are the drainage axes of the Chiche aquifer in the north and south.The analyses of the waters' physical parameters differentiated the two aquifers, Chiche aquifer having lower EC and temperature than the Ilaló aquifer. Major ions analysis revealed waters that vary between Mg-HCO3 pole and a Na-HCO3 pole in both the Chiche and Ilaló aquifers. As concentrations are higher in the Ilaló aquifer than in the Chiche aquifer. In the Chiche aquifer, As concentrations also decrease as the distance from the volcano increases. Arsenic is of natural origin, but no significant correlations were found for the Chiche aquifer. In the Ilaló aquifer a 57% correlation with Fe was found, which suggests an interaction between As and Fe oxides present in the geologic formation.Radioactive isotope 3H was not detected in groundwater from either aquifer, except in one spring in the north of the study area in the Chiche formation. The likely infiltration from recent waters was confirmed by 14C analysis this spring, which showed concentrations > 100 pmc. Other sampling points in the Chiche aquifer have 14C activities between 45.4 - 87.4 pmc. The Ilaló aquifer has 14C activities < 20 pmc. Water ages were calculated and corrected using 13C, which reveal a contamination from geogenic CO2, making water seem older than it is in reality. Despite the age correction, groundwater ages remain very old: Chiche groundwaters are between 400 - 4,000 years old and Ilaló groundwaters are between 11,000 - 44,000 years old. Stable isotopes were used to identify recharge areas. Groundwaters from Chiche aquifer show an isotopic 18O and 2H signature below the Local Meteoric Water Line (slope=3.5). This was interpreted as isotopic fractionation from hot rock and water interactions, which was not observed in the Ilaló aquifer. Recharge altitude calculations show that the Chiche aquifer is fed on the Ilaló and Pasochoa volcano piedmonts, if we consider that climatic conditions over the recharge period are close to current conditions. However, for the Ilaló aquifer, recharge areas appear to be located on the flanks of the volcano, assuming colder recharge climatic conditions than today. This recharge area should no longer be functional because of the Cangahua deposits during the last volcanic events.Results suggest that Ilaló groundwaters are being mixed with Chiche groundwaters. This research is the first to have been done with this level of detail in Ecuador on this type of aquifer and will provide new opportunities for projects in others volcano-sedimentary aquifers in the country.

Le but de ce travail de thèse est de démontrer l’intérêt d’un macrophyte aquatique submergé, Myriophyllum alterniflorum pour la détection de contaminants dans l’environnement. Des études in situ ont été réalisées pendant 28 jours sur cinq milieux aquatiques, affectés par différents types de pression anthropique, durant trois campagnes de terrain (printemps 2015, automne 2015 et printemps 2016), pour déterminer si l’accumulation des contaminants dans la plante et si des biomarqueurs du myriophylle peuvent être utilisés pour détecter la présence de contaminants dans les eaux. L’accumulation des contaminants au cours du temps était corrélée avec les teneurs des contaminants dans l’eau ; l’influence de la durée d’exposition a été étudiée. Au cours des trois campagnes, la réponse des biomarqueurs, teneur en MDA et activité de nitrate réductase était corrélée avec les teneurs en contaminants dans l’eau et dans la plante ; cependant l’influence de la durée d’exposition sur l’évolution de la réponse des biomarqueurs est moindre par rapport à celle de l’accumulation des contaminants. Ainsi, l’étude des biomarqueurs pourrait permettre une évaluation plus fiable de la qualité des masses d’eau que le suivi de l’accumulation dans la plante. Au cours de la campagne printemps 2015, un panel de biomarqueurs plus large a été étudié afin de définir les biomarqueurs les plus pertinents pour détecter spécifiquement les pressions liées aux activités urbaines ou industrielles. Une méthodologie d’évaluation de la qualité des eaux est proposée, en considérant un protocole d’analyse des biomarqueurs : un premier dosage de Chlb et MDA est simple et moins coûteux. Quand aucune preuve d'impact anthropique n'est montrée, aucune analyse complémentaire n'est requise. En revanche, lorsqu’une altération est mise en évidence, l’analyse d'autres biomarqueurs plus spécifiques tels que les activités G6PDH et γ-GCS sera nécessaire. La réponse de l'activité γ-GCS est spécifique du stress métallique, ainsi, la réponse de ce biomarqueur devrait amener à réaliser l’analyse des métaux/métalloïdes dans M. alterniflorum. / The aim of this thesis is to demonstrate the interest of a submerged aquatic macrophyte, Myriophyllum alterniflorum for the detection of contaminants in the environment. In situ studies were conducted over 28 days in five aquatic environments, affected by different levels of anthropogenic pressure, during three field seasons (spring 2015, autumn 2015 and spring 2016), to determine whether the accumulation of contaminants in the plant and whether biomarkers can be used to detect the presence of contaminants in water. The accumulation of contaminants over time was correlated with the levels of contaminants in the water; the influence of the duration of exposure has been studied. In all three campaigns, biomarker response, MDA content, and nitrate reductase activity were correlated with contaminant levels in water and in the plant; however, the influence of the duration of exposure on the evolution of the biomarker response is lower compared to the accumulation of contaminants. Thus, the study of biomarkers could allow a more reliable assessment of the quality of water bodies than the monitoring of contaminant accumulation in the plant. During the spring 2015 campaign, a much broader biomarker panel was investigated to define the most relevant biomarkers for assessing water quality. A methodology for evaluating water quality is proposed, considering a biomarker analysis protocol: a first assay of Chlb and MDA is simple and less expensive. When no evidence of human impact is shown, no further analysis is required. On the other hand, when an alteration is highlighted, the analysis of other more specific biomarkers such as G6PDH and γ-GCS activities will be necessary. The response of γ-GCS activity is specific for metal stress, so the response of this biomarker should lead to the analysis of metals / metalloids in M. alterniflorum.

In the technologically driven information age, the consumption of power is as vital to daily life as food and shelter. The generation of that power comes from a variety of sources of which coal is the predominant provider of electrical energy. Coal combustion is a well-known technology and the United States possesses the most abundant coal deposits on Earth, however, the drawback accompanying this process is the significant emissions which are released during combustion. Over the years, much effort has gone into reducing the emissions of majority constituent elements CO2, CO, NOx, SOx, etc. but it is only in the last decade or so that much attention has been given to the trace metals present within coal. Most of the work into examining these trace metals has been upon Hg and how it speciates within the flue gas in order to determine the most effective means of removal. In this study, the trace metals arsenic (As) and selenium (Se) will be investigated in a similar manner to evaluate the speciation of these elements. While previous experimental work has been performed in this area, it has been limited to thermodynamic studies which determine the speciation after equilibrium has been reached, this ignores the fact the residence times within the flue are often only several minutes during which time rapid quenching is taking place. This study takes a different approach by examining the speciation using computational chemistry which affords the advantage of being able to perform a kinetic study which is more useful in creating a flue gas model. Using ab initio the properties of various As and Se species can be evaluated compared to existing experimental data for validation. After which, a number of reactions may be selected and the structure of the transition state for each identified. Once the properties of the transition structure are known, the appropriate kinetic model, be it Transition State Theory, RRKM Theory, etc. can be applied and the rate constant determined. It is by the determination of these rate constants that the kinetic model of the flue gas can be improved and a more accurate depiction of the speciation of these race metals created.