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The objective of this study is to use a mixed flow reactor system to determine the dissolution rate and infer potential mechanisms of arsenopyrite (FeAsS) oxidation by dissolved oxygen at 25°C and circumneutral pH. Release rates for iron, arsenic and sulfur are calculated for a variety of initial dissolved oxygen (DO) concentrations. Results indicate that the rate of arsenopyrite oxidation, represented by the rate law r = A(6.76 x 10-11) where the rate, r, is in mol/s and surface area, A, is in m2, is not significantly dependent on DO concentration. Arsenic and sulfur are released in a 1:1 molar ratio while iron is released more slowly due to precipitation of iron oxyhydroxides. Our results suggest that the rate determining step in arsenopyrite oxidation is determined by the attachment of oxygen at the anodic site in the mineral, and not the transfer of electrons from the cathodic site to oxygen, as is suggested for other sulfide minerals such as pyrite. Previous work on FeAsS oxidation has been limited to low pH conditions with ferric iron as the oxidant. However, not all arsenopyrite weathering occurs exclusively in acidic environments. For example, at an abandoned arsenopyrite mine in Virginia, the pH of ground and surface waters is consistently between 4 and 7. Results of this study provide important insight to arsenic mobilization processes and rates, at field-relevant conditions, consequently aiding in the effort to understand arsenic release and retention in the environment. / Master of Science

The organoarsenical roxarsone is added to poultry feed to increase weight gain. Studies have shown that roxarsone does not accumulate in poultry tissue but is excreted, resulting in elevated arsenic concentrations (~40 mg/kg) in poultry litter. However, there is little understanding of the fate of roxarsone once it is introduced into agricultural watersheds. Using batch experiments, I investigated the sorption characteristics of roxarsone to Ap and Bt soils of the Frederick series, common in the Shenandoah Valley of Virginia, an area of intense poultry production. Results demonstrate that roxarsone sorbs strongly to Bt soils, but only showed moderate to low sorption onto Ap soils. Sorption to the Ap soils demonstrated stronger pH dependence than did sorption to the Bt soils. Removing organic matter (OM) from Ap soils significantly changed the sorption characteristics, suggesting that OM may be coating mineral surfaces in these soils. Results of this study have implications for roxarsone transport in agricultural watersheds. For soils that have had years of poultry litter application, there will be both sorption and subsequent leaching of roxarsone. In the OM-rich Ap horizon, OM controls sorption. Because roxarsone is loosely bound to OM, it would be rapidly leached into water after a recharge event or field irrigation. Once roxarsone reaches the Bt soils, it is strongly sorbed into iron oxides or clays, decreasing the potential for leaching. However, competition from phosphate or organic acids for sorption sites on mineral surfaces may affect roxarsone retention in the Bt soils. / Master of Science

OBJECTIF: Évaluer l’association entre les niveaux d’arsenic urinaire et la prévalence du diabète de type 2 dans la population canadienne. MÉTHODES : L’étude a concerné 3517 adultes participant à l’Enquête canadienne sur les mesures de santé réalisée de 2007 à 2009. Tous les participants ont eu une prise de sang pour la détermination du glucose et de l’hémoglobine glyquée ainsi qu’une analyse d’urine pour la détermination de l’arsenic total. De plus, ils ont répondu à un questionnaire détaillé sur leurs habitudes de vie et leurs antécédents médicaux. L’analyse statistique a utilisé la régression logistique multivariée. RÉSULTATS : L’As total urinaire est positivement associé au diabète de type 2 et au pré-diabète : Rapport de cotes ajusté de 1,81 (IC à 95%: 1,12 à 2,95) et 2,04 (IC à 95% CI: 1,02 à 4,07) respectivement. L’As total urinaire est aussi associé avec le taux d’hémoglobine glyquée chez les diabétiques non traités. CONCLUSION : L’association entre l’exposition à l’arsenic et la prévalence de diabète et de pré-diabète est observée dans la population canadienne. / OBJECTIVES: This study evaluated the association between As exposure, as measured by total As concentration in urine, and the prevalence of type 2 diabetes. METHODS: The study involved 3517 adults who participated in the Canadian Health Measures Survey (CHMS) carried out from 2007 to 2009. All participants had a blood test for glucose and glycated hemoglobin determination. Urine analysis was also performed for total arsenic determination. In addition, participants answered a detailed questionnaire about their lifestyle and medical history questionnaire. Statistical analysis was performed using multivariate logistic regression to identify significant relationships, while adjusting for potential confounders. RESULTS: Total urinary As is positively associated with type 2 diabetes and pre- diabetes: Adjusted odds ratio of 1.81 (95% CI: 1.12 to 2.95) and 2.04 (95% CI: 1.02 to 4.07), respectively. Total urinary As is also associated with glycated hemoglobin in untreated diabetics. CONCLUSIONS: The association between arsenic exposure and the prevalence of diabetes and pre-diabetes is observed in the Canadian population.

Arsenic is a prevalent contaminant at a large fraction of US Superfund sites. Therefore, establishing techniques for accelerating As remediation could benefit many contaminated sites. Remediation of As contaminated groundwater by conventional methods, i.e. pump and treat (P&T), can be impeded by slow desorption of As from Fe and Al (hydr)oxides in aquifer solids. Through experimentation at different physical scales (grain, bench, and field scale), the potential for chemical additions to increase As release from sediments and possibly accelerate P&T remediation is examined. The work described here focuses on As contamination and remediation at the Vineland Chemical Co. Superfund site in southern NJ. The site is extensively contaminated with As resulting from decades of poor chemical storage and disposal practices by the Vineland Chemical Co., which manufactured As-based biocides from 1949-1994. Despite significant intervention, including groundwater remediation by P&T and treatment of solids via soil washing, sufficient site clean up could require many decades with current technologies. Chemical amendments that either compete with As for sorption sites or dissolve Fe and Al (hydr)oxides can increase As mobility and potentially improve P&T remediation efficiency. Simple extrapolations from bench scale column experiments based on pore volumes suggest that treatment with 10 mM oxalic acid could lower the time necessary for clean up at the Vineland site from 600 years (with current techniques involving just groundwater) to potentially on the order of 4 years. Small scale (<1 mm2) X-ray fluorescence maps from columns performed within the synchrotron beamline showed As release during oxalic acid treatment that was consistent with the bulk column materials and suggested that microscale processes can be predictive of the larger system. Finally, during a 3-month pilot study at the Vineland site, oxalic acid was injected into a section of the aquifer via an injection manifold system that was designed and built for the experiment. Groundwater samples indicate that introduction of oxalic acid led to increased As release at a sampling well and pump and treat recovery well in the study area. Addition of oxalic acid shows promise for accelerating treatment of a highly contaminated site.

Background: Over 200 million individuals worldwide are chronically exposed to arsenic (As) in drinking water at concentrations above the World Health Organization (WHO) guideline of 10 µg/L. Arsenic exposure is of particular concern in Bangladesh, where it is estimated that 35-77 million people are exposed to As in well water at concentrations above the WHO guideline. Chronic As exposure is associated with neurological impairments, respiratory disease, cardiovascular disease, skin lesions, and cancers of the skin, liver, lung and bladder. The mechanisms of As toxicity in humans are not well-characterized: there are considerable interspecies differences in As toxicokinetics, and until recently, there were no animal models to study As carcinogenesis. However, two of several proposed pathways of As toxicity in humans involve DNA methylation and oxidative stress. Arsenic metabolism, DNA methylation, and glutathione (GSH) are metabolically connected through the one-carbon metabolism and transsulfuration pathways, and their interactions are remarkably complex. The epidemiologic studies in this dissertation are designed to address the overarching hypothesis that one-carbon metabolism and the transsulfuration pathway interact to influence susceptibility to As toxicity. Introduction: Arsenic is methylated in the liver to monomethyl (MMA) and dimethyl (DMA) arsenical species by arsenic(III)-methyltransferase (AS3MT), which requires a methyl group from S-adenosylmethionine (SAM) and the presence of a reductant, such as glutathione (GSH). SAM is the universal methyl donor for transmethylation reactions, including DNA methylation, and is a product of folate-dependent one-carbon metabolism. GSH is the primary endogenous antioxidant and determinant of the intracellular redox state, and the rate-limiting precursor for GSH synthesis, cysteine (Cys), is a product of the transsulfuration pathway. One-carbon metabolism and the transsulfuration pathway are connected through homocysteine (Hcys). In humans, aberrant DNA methylation, oxidative stress, hyperhomocysteinemia (HHcys), and impaired As methylation capacity have been identified as risk factors for As-related conditions, including As-induced skin lesions. However, there are knowledge gaps regarding the relationships among these risk factors in humans, namely (1) the dose-response relationship between chronic As exposure and global DNA methylation over a wide range of As concentrations, as well as the influence of As exposure on the newly-discovered epigenetic modification, 5-hydroxymethylcytosine (5hmC); (2) whether an oxidized GSH redox state impairs the capacity to methylate As and DNA; and (3) whether variants in one-carbon metabolism genes are associated with HHcys and susceptibility to As-induced skin lesions. Methods: We addressed these questions in five self-contained epidemiological studies of As-exposed Bangladeshi adults, which employed cross-sectional (Chapters 3-6) and nested case-control (Chapter 7) designs. First, we examined the dose-response relationship between As exposure and global methylation of peripheral blood mononuclear cell (PBMC) DNA (Chapter 3). Second, we optimized a high-throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay to measure global 5-methylcytosine (5mC) and 5hmC content in human DNA samples, and we examined the associations of As exposure with global %mC and %hmC in two independent samples of As-exposed adults (Chapter 4). Third, we measured GSH and its "oxidized" form, glutathione disulfide (GSSG) in plasma, and we examined the interaction of plasma GSH redox state and folate nutritional status on As methylation capacity (Chapter 5). Fourth, we examined the relationships between blood GSH redox, blood SAM, and global methylation of PBMC DNA (Chapter 6). Fifth, we conducted a nested case-control study (Chapter 7) to determine whether nonsynonymous single nucleotide polymorphisms (SNPs) in methylene-tetrahydrofolate reductase (MTHFR) and other one-carbon metabolism genes were associated with HHcys and risk for As-induced precancerous skin lesions, and we conducted an exploratory genome-wide association study (GWAS) of Hcys in a subset of participants. Results: Chronic As exposure was associated with increased global DNA methylation over a wide range of well water As concentrations (Chapter 3), but the relationship between As exposure and global %hmC was gender-specific, with a positive association in males and negative association in females (Chapter 4). We found that an oxidized GSH redox state was associated with both decreased As methylation capacity (Chapter 5) and global DNA hypomethylation (Chapter 6). Finally, in the nested-case control study, we confirmed previous findings that serum HHcys was a risk factor for As-induced skin lesions, and gene variants in MTHFR were found to explain a substantial proportion of the variance in serum Hcys concentrations (Chapter 7). However, we did not find that one-carbon metabolism gene variants were risk factors for As-induced skin lesions. The GWAS of serum Hcys identified one genome-wide significant SNP in the pregnane X receptor (PXR) gene, along with other SNPs in genes involved in cell signaling and the establishment of epithelial cell polarity. Taken together, our findings suggest that indices of one-carbon metabolism and the transsulfuration pathway--DNA methylation, GSH redox, and As methylation--interact with one another to influence susceptibility to As toxicity in humans. In addition, to our knowledge, this is the first report of an association between As exposure and global 5hmC.

Thesis (M.S.)--Rochester Institute of Technology, 2007. / Typescript. Includes bibliographical references (leaves 33-36).

The presence of naturally occurring arsenic in groundwater has caused a number of social and health-related problems for the rural poor of Bangladesh. Today, it is estimated that 42 – 60 million people in Bangladesh consume water at arsenic concentrations greater than the World Health Organization (WHO) standard of 10 μg/L. The arsenic-iron removal plant (AIRP) has been widely used to remove arsenic from drinking water across much of the country; however, AIRPs show variable levels of efficiency and have often failed to meet the WHO standard. Those who continue to drink water with elevated concentrations of arsenic are prone to skin disease and various cancers. The thesis presented here examines methods to mitigate exposure of the rural poor to arsenic by modifying the AIRP and increasing our understanding of the chemical and social factors associated with its use. This objective is accomplished via four channels: (1) assessment of the chemical processes occurring within the AIRP, (2) evaluation of three retrofits, (3) development of a waste management strategy, and (4) examination of social factors affecting use and sustainability of the AIRP. Household AIRPs installed in the village of Mohadevpur, in the Manikganj district, are examined.

Thesis--Auburn University, 2006. / Abstract. Includes bibliographic references (p.70-84).

Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Oct. 5, 2009). Includes bibliographical references.