Une étude a été menée sur la faisabilité technique du traitement de potabilisation des eaux de forage contaminées à l’arsenic par procédé membranaire. Pour ce faire, l’efficacité de deux membranes commerciales (NF270 et TW30) vis-à-vis de la rétention des espèces d’arsenic, arsénite [As (III)] et arséniate [As (V)], a été d’abord comparée sous différentes conditions expérimentales. Ensuite, la contribution des différents mécanismes intervenant dans l’élimination des espèces d’arsenic a été identifiée. Enfin, la membrane la plus performante a été utilisée pour le traitement d’une eau souterraine naturellement riche en arsenic. Il ressort de cette étude que la pression opératoire et le pH sont les paramètres importants sur lesquels il faut agir pour améliorer l’efficacité du système membranaire pour le traitement de l’arsenic. L’As(V) est facilement éliminé par rapport à l’As (III) aussi bien avec la membrane de nanofiltration que d’osmose inverse. Toutefois, la membrane d’osmose inverse (TW30) permet une meilleure élimination des différentes espèces d’arsenic que la membrane NF270. Cela est dû au fait que la membrane TW30 est une membrane dense. L’application de cette membrane pour la production d’eau potable à partir d’une eau de forage contenant 413,74µg/L d’arsenic total dont 405,63µg/L d’As (V) et 8,11 µg/L d’As (III) a donné une concentration d’arsenic total dans l’eau traitée de 9,99 µg/L soit un taux de rétention de 97,6% et un volume d’eau traité correspondant à 70% du volume d’eau brute. Il est donc possible de mettre en place un procédé de traitement de ces eaux de forage à partir de la membrane TW30 afin de produire de l’eau potable pour les populations du nord du Burkina Faso. La performance de ce procédé peut être encore améliorée en oxydant l’As (III) en As (V) avant filtration. / In order to produce potable water for human consumption, a study was carried out on the technical feasibility of arsenic-rich borehole water treatment by membrane process. Firstly the efficiency of two commercial membranes (NF2Une étude a été menée sur la faisabilité technique du traitement de potabilisation des eaux de forage contaminées à l’arsenic par procédé membranaire. Pour ce faire, l’efficacité de deux membranes commerciales (NF270 et TW30) vis-à-vis de la rétention des espèces d’arsenic, arsénite [As (III)] et arséniate [As (V)], a été d’abord comparée sous différentes conditions expérimentales. Ensuite, la contribution des différents mécanismes intervenant dans l’élimination des espèces d’arsenic a été identifiée. Enfin, la membrane la plus performante a été utilisée pour le traitement d’une eau souterraine naturellement riche en arsenic. Il ressort de cette étude que la pression opératoire et le pH sont les paramètres importants sur lesquels il faut agir pour améliorer l’efficacité du système membranaire pour le traitement de l’arsenic. L’As(V) est facilement éliminé par rapport à l’As (III) aussi bien avec la membrane de nanofiltration que d’osmose inverse. Toutefois, la membrane d’osmose inverse (TW30) permet une meilleure élimination des différentes espèces d’arsenic que la membrane NF270. Cela est dû au fait que la membrane TW30 est une membrane dense. L’application de cette membrane pour la production d’eau potable à partir d’une eau de forage contenant 413,74µg/L d’arsenic total dont 405,63µg/L d’As (V) et 8,11 µg/L d’As (III) a donné une concentration d’arsenic total dans l’eau traitée de 9,99 µg/L soit un taux de rétention de 97,6% et un volume d’eau traité correspondant à 70% du volume d’eau brute. Il est donc possible de mettre en place un procédé de traitement de ces eaux de forage à partir de la membrane TW30 afin de produire de l’eau potable pour les populations du nord du Burkina Faso. La performance de ce procédé peut être encore améliorée en oxydant l’As (III) en As (V) avant filtration.70 and TW30) for different arsenic species removal, arsenite [As (III)] and arsenate [As (V)], was compared under various experimental conditions. Afterward, the contribution of mechanisms in As species removal was determined. Finally, the most efficient membrane was used for As-rich groundwater treatment. Results show that, applied pressure and feed pH are the important parameters which must be considered if As removal wants to be improved. As (V) is much easily removed than As (III) both NF270 and TW30 membranes. Nevertheless, TW30 membrane has a better removal of As species than NF270 membrane. It is due to the fact that TW30 membrane is a compact membrane. The application of this membrane for potable water production from naturally contaminated groundwater containing 413.74 µg/L of total arsenic (405.63 µg/L of As (V) and 8.11 µg/L of As (III)) gave a treated water of 9.99 µg/L (97.6% of rejection) of total As concentration and water produced volume equivalent to 70% of raw water volume. Therefore, it is possible to implement a treatment process with TW30 membrane to remove arsenic from naturally contaminated groundwater coming from the northern part of Burkina Faso. The efficiency of this process can be improved again by oxidizing As (III) in As (V) before filtration.

Elevated concentrations of arsenic in groundwater pose a public health threat to millions of people worldwide. While arsenic is an established human carcinogen, a mode of action has yet to be determined for arsenic carcinogenesis. However, the oxidative stress and DNA repair pathways have been implicated in arsenic toxicity and have been hypothesized to underlie arsenic carcinogenesis. To date, few epidemiologic studies have evaluated genetic susceptibility to arsenical skin lesions based on single nucleotide polymorphisms (SNPs) in antioxidant enzyme or DNA repair genes. Utilizing cross-sectional data from the 2000-2002 survey of the Health Effects of Arsenic Longitudinal Study (HEALS) for 610 prevalent arsenical skin lesion cases and 1,079 randomly selected controls, I evaluated the associations of SNPs in genes encoding antioxidant enzymes and DNA repair enzymes on skin lesion prevalence. I also evaluated potential interactions between the SNPS as well as SNP-environment interactions in determining skin lesion prevalence. In the first study of this dissertation (Chapter 2), I assessed the relationship between SNPs in antioxidant enzyme genes and skin lesion prevalence, as well as possible interactions of these associations on the additive scale by various environmental factors. There were no statistically significant associations between these SNPs (SOD2, rs4880; CAT, rs1001179; GPX1, rs1050450; and MPO, rs2333227) and skin lesion prevalence. Additionally, there was no evidence of additive interaction by arsenic exposure levels, body mass index, smoking status, or fruit and vegetable intake with the SNPs in relation to skin lesion prevalence. However, there was marginal evidence that skin lesion prevalence was increased among individuals who carried 4 or more risk alleles compared to individuals carrying 0-3 risk alleles in these SNPs. Additionally, I observed a significant departure from additivity for the risk allele score and primary methylation index on skin lesion prevalence. In the second study of this dissertation (Chapter 3), I assessed the relationship between SNPs in DNA repair genes (OGG1, rs1052133; XRCC1, rs25487 and rs1799782; XRCC3, rs861539; ERCC2, rs1052559; ERCC5, rs17655; and LIG4, rs1805388) and skin lesion prevalence, as well as possible interactions of these associations on the additive scale by various environmental factors. In logistic regression models controlling for sex, age, and well water arsenic concentration, no associations were observed between measured SNPs and skin lesion prevalence. The results did not vary by arsenic exposure levels, body mass index, or smoking status. However, I did observe a significant inverse association of total fruit and vegetable consumption with skin lesion prevalence, and its additive interaction with the polymorphism in ERCC5. In the third study of this dissertation (Chapter 4), I utilized a multi-analytic approach to explore gene-gene, gene-environment, and higher-order interactions among 10 SNPs related to the oxidative stress and DNA repair pathways by MDR, CART, and logistic regression models. As shown in Chapters 2 and 3, none of these SNPs were associated with skin lesion prevalence, however, were evaluated for potential SNP-SNP interactions. MDR and CART modeling approaches were utilized for the selection of potential gene-gene and gene-environment interactions. Considerable overlap of the interactions detected by both these methods was observed, which were further evaluated by logistic regression. Results from logistic regression modeling, provided some evidence of these statistical interactions; however, their biological interpretation was limited. In summary, there was marginal evidence that skin lesion prevalence was increased among individuals who carried 4 or more risk alleles in genotyped SNPs related to the oxidative stress pathway compared to individuals carrying 0-3 risk alleles in these SNPs and, a significant departure from additivity was observed for the risk allele score and primary methylation index on skin lesion prevalence. Additionally, a significant inverse association of total fruit and vegetable consumption with skin lesion prevalence was observed and, a significant interaction between the polymorphism in ERCC5 and total fruit and vegetable intake was observed in relation to skin lesion prevalence on the additive scale. However, these finding require replication in other studies.

Background: In the country of Bangladesh, arsenic (As) exposure and high plasma homocysteine (hyperhomocysteinemia; HHcys) are widely prevalent. An estimated 35-77 million people in Bangladesh are exposed to As above the World Health Organization standard of 10 μg/L, while a cross-sectional study by our group estimated that 63% of men and 26% of women had HHcys. Both As exposure and HHcys are associated with adverse health outcomes. Arsenic exposure is an established cause of skin, lung, and bladder cancer, and cardiovascular disease, while HHcys is a strongly associated with increased risk for cardiovascular disease. Chronic kidney disease is emerging as an As-linked disease outcome. Potential mechanisms for adverse health effects induced by As (e.g. nephrotoxicity) include oxidative stress and inflammation. Inorganic As is metabolized through a series of methylation and reduction reactions which facilitate As excretion in urine; arsenite (AsIII), the primary form of As in Bangladesh drinking water, is converted to monomethylarsonic acid (MMAV), monomethylarsonous acid (MMAIII), and dimethylarsinic acid (DMAV). The methyl donor for these methylation reactions is S-adenosylmethionine (SAM). Because the availability of SAM is modulated by various nutritional parameters, nutritional interventions have the potential to enhance As methylation. Supplementation with folic acid (FA), which increases liver SAM, has been shown by our group to enhance As methylation and lower blood As in folate-deficient Bangladeshi adults. The endogenous synthesis of creatine from guanidinoacetate (GAA) consumes a large proportion of SAM, and creatine supplementation in the diet can downregulate endogenous creatine synthesis by inhibiting GAA production. In this way, creatine supplementation has the potential to spare SAM, enhance As methylation, and also lower homocysteine (Hcys), a by-product of SAM-dependent methylation. The potential for dietary creatine to enhance As methylation may explain the frequently observed associations of urinary creatinine with a decreased proportion of inorganic As in urine out of total urinary As (u%InAs), and an increased proportion of DMA in urine out of total urinary As (u%DMA) in epidemiological studies. Alternatively, it is possible that these associations are due to confounding by renal function, which could influence both As and creatinine excretion. Objectives: Our objectives were to determine (1) whether folic acid and creatine lower blood As in a mixed folate-deficient and replete population, (2) whether creatine lowers plasma total homocysteine (tHcys), (3) whether As exposure is associated with increased inflammation and decreased estimated glomerular filtration rate (eGFR), and whether these effects are greater in those with a more oxidized plasma glutathione redox potential (EhGSH), and (4) whether As metabolite proportions in urine and blood are associated with eGFR, and whether these associations may explain the relationship between As metabolite proportions and urinary creatinine. Methods: We addressed these objectives in five epidemiologic investigations of As-exposed Bangladeshi adults, employing data from a randomized placebo-controlled trial (the Folic Acid and Creatine Trial (FACT)) and two cross-sectional studies (the Nutritional Influences on Arsenic Toxicity (NIAT) study, and the Folate and Oxidative Stress (FOX) study). In the 24-week FACT study, participants were randomized to receive either placebo, 400 μg/day FA (FA400), 800 μg/day FA (FA800), 3 g/day creatine (Cr), or 3 g/day creatine + 400 μg/day FA (Cr+FA400). At week 12, half of the participants in the FA400 and FA800 groups were switched to placebo, while the other half continued their assigned supplements. Additionally, at week 12 participants in the Cr and Cr+FA400 groups were switched to placebo. In Chapter 4 (FACT), we examined whether FA400, FA800, Cr, or Cr+FA00 lowered blood As to a greater extent than placebo over the first 12 weeks of the trial, and whether a rebound in blood As occurred from week 12 to 24 related to cessation of FA supplementation. In Chapter 5 (FACT), we examined whether Cr or Cr+FA400 lowered plasma tHcys to a greater extent than placebo or FA400 alone, respectively, over the first 12 weeks of the trial. In Chapter 6 (NIAT), we examined the associations of water and urinary As with eGFR, and whether eGFR confounded the associations between urinary creatinine and the urinary %As metabolites; we also explored the associations of eGFR with the urinary %As metabolites. In Chapter 7 (FOX), we examined the associations of eGFR with the urinary and blood %As metabolites; we also examined whether the relationship between blood and urinary %As metabolites was decreased among those with reduced renal function. In Chapter 8 (FOX), we examined the associations of water, blood, and urinary As with markers of inflammation (C-reactive protein (CRP) and α-1 acid glycoprotein (AGP)), and eGFR, and investigated whether these associations were modified by the plasma EhGSH. Results: FA800 lowered blood As to a significantly greater extent than placebo over the 24 weeks of the FACT study, with no rebound in blood As related to cessation of FA supplementation. FA400, Cr, and Cr+FA400 did not lower blood As to a greater extent than placebo (Chapter 4). Cr and Cr+FA400 did not lower plasma tHcys to a greater extent than placebo or FA400 alone, respectively. However, in the Cr+FA400 group we observed a significant correlation between a decrease in plasma GAA over time and a decrease in plasma tHcys over time (Chapter 5). Total urinary As was marginally associated with a decrease in eGFR in the NIAT study, though water As was not. Additionally in the NIAT study, while eGFR did not confound the relationship between urinary creatinine and urinary %As metabolites, we observed a positive association between eGFR and u%InAs, and a negative association between eGFR and u%DMA (Chapter 6). Likewise in the FOX study, eGFR was positively associated with u%InAs and negatively associated with u%DMA; the associations of eGFR with the blood %As metabolites were in the same direction, although not statistically significant. We additionally observed that for a given increase in blood %InAs, the increase in urinary %InAs tended to be smaller in those with reduced renal function, compared to those with normal renal function (Chaper 7). In the FOX study we also observed the total blood As and urinary As were marginally associated with decreased eGFR, while water As was not. Water As, urinary As, and blood As were significantly positively associated with plasma CRP in those with low plasma GSH or a more oxidized plasma EhGSH (Chapter 8). Conclusions: Strategies to reduce risk for As-induced diseases are sorely needed, particularly due to barriers to As exposure removal and/or persistent elevated risk from past As exposure. Several susceptibility factors which can potentially be intervened upon have been discussed in this dissertation, namely folate nutritional status, redox status, and renal capacity to excrete As. Our finding that folic acid supplementation (800 μg/day) lowered blood As to a greater extent than placebo in a randomized trial indicates that improving the folate status of the general Bangladeshi population may reduce the body burden of As. Folate fortification of food in Bangladesh, in addition to potentially reducing risk for As-induced diseases, would have the additional benefit of substantially lowering the prevalence of HHcys. Our finding in a cross-sectional study that individuals with a more oxidized plasma glutathione redox potential were susceptible to As-induced inflammation may indicate that improving redox status can protect against As-induced inflammation. Randomized trials are needed to confirm a protective effect of antioxidants; upon confirmation, antioxidant dietary recommendations for As-exposed populations could potentially be implemented. Finally, our cross-sectional finding of a positive association between eGFR and urinary %InAs, and that eGFR modified the relationship between blood and urinary %InAs, suggests that InAs excretion may be impaired among individuals with reduced renal function. A decreased renal capacity to excrete InAs may lead to accumulation of InAs in tissues, and related health effects. Potential interventions related to renal function include treatment of risk factors for chronic kidney disease (e.g. blood pressure, blood glucose) in order to prevent onset of renal function deterioration, or to screen for chronic kidney disease in order to identify susceptible individuals and conduct directed interventions. Of these three susceptibility factors, the strongest evidence exists for the potential of folic acid to lower blood As. In Bangladesh, where As exposure and HHcys are widely prevalent, folate fortification should be considered a viable option for reducing risk for As- and Hcys-related diseases.

Thesis (M.Sc. (Biochemistry)) -- University of Limpopo, 2019 / Survivin is the smallest and a well-studied member of the inhibitors of apoptosis proteins (IAPs) family, which is involved in the regulation of cell division, inhibition of both caspasedependent and -independent apoptosis in cancer cells and promotion of angiogenesis. Survivin is detectable during embryonic and foetal development but is undetectable in normal adult tissues. It is, however, expressed in transformed cell lines as well as in most common types of human cancers. Regulation of survivin remains poorly understood, and the discovery of the regulatory biomolecules, microRNAs (MiRs) present an interesting opportunity to investigate the regulation of this protein and its variants in cancers, especially breast cancer. Additionally, the expression of the survivin splice variants during cell cycle progression and apoptosis is not fully understood. The aims of this study were to investigate the role of arsenic trioxide on the expression of survivin splice variants and their specific microRNAs during cell cycle progression and apoptosis in human breast cancer MCF-7 cells. The study also aimed at ascertaining the toxicity and efficacy of using coal fly ash-derived β-cyclodextrin carbon nanospheres to deliver arsenic trioxide into the MCF-7 cells. Carbon nanospheres (CNSs) were synthesised using a chemical vapour deposition method while arsenic trioxide was deposited using wet impregnation method to form the arsenic trioxide-β-cyclodextrin carbon nanospheres (ATO-β-cyclodextrin-CNSs). The formation of the CNSs and the loading of arsenic trioxide to CNSs were confirmed using scanning electron microscopy/energy dispersive X-ray detection (SEM-EDX). The in vitro cytotoxicity effect of the β-cyclodextrin carbon nanospheres (CNSs), arsenic trioxide and arsenic trioxide-β-cyclodextrin CNSs against KMST-6 and MCF-7 cells was analysed using the 3-(4, 5-dimethylthiazol-2-yl)-2, 5 diphenyltetrazolium bromide (MTT) Assay, Muse® Count and Viability Assay and light/fluorescence microscopy. Cellular apoptosis, cell cycle analysis, Multi-Caspase activation, mitochondrial membrane potential, MAPK activation and PI3K activation were analysed using the Muse® Cell Analyser. Polymerase Chain Reaction (PCR) and Immunohistochemistry were used to analyse survivin mRNA variants and protein expression, respectively. The survivin specific MiRs were predicted using both bioinformatics platforms and literature surveys. In order to understand the applicability of delivering arsenic trioxide for the treatment of breast cancer, skin fibroblast (KMST-6) and MCF-7 cells were exposed to β-cyclodextrin CNSs. The novel β-cyclodextrin CNSs did not show any cytotoxic effect on the KMST-6 cells but demonstrated such activity against the MCF-7 cells. More so, arsenic trioxide-βcyclodextrin CNSs were found to significantly reduce the viability of the MCF-7 cells and were shown to inhibit their cell growth through the induction of apoptosis. The MTT Assay results revealed arsenic trioxide inhibited the growth of the MCF-7 cells in a concentration-dependent manner. The Muse® Cell Analyser showed that arsenic trioxide induced G2/M cell cycle arrest and promoted cellular apoptosis without any damage to the mitochondrial membrane of MCF-7 cells. Furthermore, arsenic trioxide also deactivated two survival pathways, Mitogen-Activated Protein Kinase (MAPK) and Phosphoinositide 3-Kinase (PI3K) signalling pathways in MCF-7 cells. The deactivation of the two pathways was shown to be accompanied by the upregulation of survivin 3α during arsenic trioxide-induced G2/M cell cycle arrest and apoptosis. Survivin 2B was found to be upregulated only during arsenic trioxide-induced G2/M cell cycle arrest, but downregulated during arsenic trioxide-induced apoptosis. However, wild-type survivin was highly expressed in untreated MCF-7 cells, but the expression was upregulated during arsenic trioxide-induced G2/M cell cycle arrest and was downregulated during arsenic trioxide-induced apoptosis. Survivin variant ΔEx3 was undetected in both untreated and treated MCF-7 cells. Survivin 2α was upregulated during arsenic trioxideinduced apoptosis whereas, survivin 3B was only detected in the untreated MCF-7 cells. Additionally, survivin proteins were localised in both the nuclei and cytoplasm in MCF-7 cells and highly upregulated during arsenic trioxide-induced G2/M cell cycle arrest, which can be attributed to the upregulation of survivin-2B. Using TargetScan, MIRD and mirTarbase, a few MiRs were identified and confirmed to target wild-type survivin, survivin 2B and survivin ΔEx3. These include the MiR-542-3p and MiR-335-5p, which are both upregulated during apoptosis and MiR-218-5p, which is upregulated during cell arrest. MiR-218-5p targets survivin 2B, which was upregulated during G2M cell cycle arrest. The fly ash-derived CNSs can be used to deliver arsenic trioxide for therapeutic purposes, especially against breast cancer. Most importantly, these nanoparticles induced typical apoptotic characteristics in breast cancer MCF-7 cells. Arsenic trioxide can be used as therapeutic target for breast cancer treatment and nanotechnology can be used for its delivery. This study provided the first evidence that novel survivin 2B splice variant may be involved in the regulation of arsenic trioxide-induced G2/M cell cycle arrest only. This splice variant can therefore, be targeted for therapeutic purposes against Luminal A breast cancer cells

Background: Chronic arsenic (As) exposure in a global public health concern. Arsenic exposure through drinking water affects over 140 million people in at least 70 countries, including 40 million people in Bangladesh. In the United States (US), 2.4 million people rely on private wells or public water systems with As levels above the US maximum contaminant level. Ingested inorganic arsenic (InAs) is methylated to monomethyl (MMAs)- and dimethyl (DMAs)-arsenical species using the methyl donor S-adenosylmethionine (SAM). Full methylation of InAs to DMAs decreases As toxicity and facilitates urinary As excretion. Arsenic methylation capacity is influenced by nutrients involved in one-carbon metabolism (OCM), the biochemical pathway that synthesizes SAM. Folate recruits one-carbon units for the remethylation of homocysteine and the synthesis of SAM. The availability of one-carbon units is also impacted by nutrients including the alternative methyl donor betaine, its precursor choline, and possibly the cofactor vitamin B12. In addition, As methylation capacity may also be influenced by creatine; an estimated 50% of SAM is consumed by the final step of endogenous creatine synthesis. The adverse health outcomes associated with chronic As exposure include impaired intellectual function, cardiovascular disease, diabetes, inflammation, and cancers of the bladder, lung, kidney, liver, and skin. In utero As exposure is associated with adverse birth outcomes include decreased birth weight and gestational age. Elevated health risks persist after exposure has been reduced or ended, leading to the hypothesis that epigenetic dysregulation, including changes in DNA methylation, may be a biological mechanism linking As exposure to health outcomes. Objectives: This research has three main objectives: (1) to investigate the influence of OCM nutritional factors on As methylation by evaluating effects of folic acid (FA) and creatine supplementation on As methylation capacity, and effect modification by baseline status of OCM-related nutrients; (2) to examine associations between As exposure and loci-specific DNA methylation in an epigenome-wide association study (EWAS); and (3) to assess mediation of the association between in utero As exposure and birth outcomes (i.e., gestational age and birth weight) by DNA methylation of target genes identified in an EWAS, as well as the candidate gene DNA methyltransferase 3 alpha (DNMT3A), a protein-coding gene involved in de novo DNA methylation. Methods: This research used data from three studies of As-exposed individuals. To address the first objective, we used data from the Folic Acid and Creatine Trial (FACT), a 24-week randomized clinical trial of FA (400 or 800 μg/day) and/or creatine supplementation (3 g/day or 3 g creatine and 400 μg FA/day) among As-exposed adults in Bangladesh recruited independent of folate status (N = 622). We investigated overall FA and creatine treatment effects on mean within-person changes in As metabolite proportions in urine compared to the placebo group (weeks 0 to 12). Rebound of As methylation capacity following the cessation of FA supplementation was assessed from weeks 12 to 24. We also assessed effect modification by baseline choline, betaine, vitamin B12, and plasma folate of treatment effects on changes in homocysteine, guanidinoacetate (GAA) (biomarkers of OCM and endogenous creatine synthesis, respectively), total blood As, and urinary As metabolite proportions and indices. To address the second objective, we used data from the Strong Heart Study (SHS), a population-based prospective cohort of American Indians with low-moderate levels of As exposure. DNA methylation was measured in 2,325 participants using the Illumina MethylationEPIC array, which interrogates > 850,000 loci. We tested for differentially methylated positions (DMPs) and regions (DMRs), and conducted gene ontology (GO) enrichment analysis to understand functions of genes containing differential methylation. To address the third objective, we used data from a prospective birth cohort in Bangladesh. In a discovery phase, an EWAS was conducted to identify CpGs with methylation measured in cord blood that are associated with maternal water As levels and birth outcomes (N = 44). In a validation phase, DNA methylation in cord blood was measured using bisulfite pyrosequencing at three target CpGs annotated to miR124-3, MCC, and GNAL (N = 569). We applied structural equation models (SEMs) to assess mediation of the association between in utero As exposure and gestational age by DNA methylation. In addition, mediation of the association between in utero As exposure and birth outcomes by DNA methylation of the candidate gene DNA methyltransferase alpha (DNMT3A) was assessed. Results: In FACT, the mean within-person decreases %InAs and %MMAs and increase in %DMAs were greater among all groups receiving FA supplementation at weeks 6 and 12 compared to placebo (P < 0.05) (Chapter 3). Stratified by median choline and betaine concentrations at baseline, we observed a trend towards greater FA treatment effects among participants with levels below the median of both nutrients compared to participants above the median (Chapter 4). Among participants who discontinued FA supplementation, at week 24, %InAs and %DMAs were not significantly different than baseline levels, suggesting a rebound in As methylation capacity with cessation of FA supplementation. We observed a significantly greater mean within-person decreases in %MMAs with creatine supplementation compared to placebo at weeks 1, 6, and 12; mean within-person changes in %InAs and %DMAs did not differ significantly between the creatine and placebo groups (Chapter 3). The mean within-person decrease in urinary %MMAs at week 12 with creatine treatment was significantly greater than placebo among participants with baseline choline concentrations below the median, but did not differ from placebo among participants with choline concentrations above the median (Chapter 4). In an EWAS conducted in SHS, we identified 20 DMPs associated with urinary As levels at FDR < 0.05; five DMPs were significant at PBonferroni < 0.05 (Chapter 5). The top significant CpG, cg06690548, was located in solute carrier family 7 member 11 (SLC7A11 ), part of the amino-acid transporter cystine:glutamate antiporter system xc-, which is involved in biosynthesis of the endogenous antioxidant glutathione (GSH). Additional Bonferroni-significant CpGs were located in ANKS3, LINGO3, CSNK1D, and ADAMTSL4. We identified one FDR-significant DMR (chr11:2,322,050-2,323,247) including the open reading frame C11orf21 and tetraspanin 32 (TSPAN32 ). Mediation of the association between in utero As exposure and birth outcomes by cord blood DNA methylation was assessed in a Bangladeshi birth cohort. In the discovery phase (N = 44), the association between maternal water As levels and gestational age was fully mediated by DNA methylation of the top 10 CpGs associated with both variables. In a discovery phase (N = 569), there were significant indirect effects of maternal water As levels on gestational age through DNA methylation of miR124-3 and MCC ; the indirect effect through DNA methylation of GNAL was not significant (Chapter 6). In an adjusted SEM including miR124-3 and MCC, mediation of the association between in utero As exposure and gestational age by DNA methylation of miR124-3 was borderline significant (P = 0.06); DNA methylation of MCC did not act as a mediator. We also assessed mediation by DNA methylation of DNMT3A (Chapter 7). In an adjusted SEM including birth weight and gestational age, there was a significant indirect effect of maternal toenail As levels on gestational age through DNMT3A methylation, the indirect effect on birth weight was borderline significant (P = 0.082). However, the indirect effects of maternal toenail As levels on birth weight through all pathways including gestational age were statistically significant. A doubling in maternal toenail As concentrations had a total effect of a decrease in gestational age of 2.1 days and a decrease in birth weight of 28.9 g. Conclusions: Results from FACT (Chapters 3 and 4) provide evidence of the associations between OCM-related nutrients and As methylation capacity. Specifically, FA and creatine supplementation may increase As methylation capacity by increasing the availability of SAM, and treatment effects may be greater among individuals with low betaine and choline status, respectively. In addition, results reported in Chapters 5-7 support the hypotheses that chronic As exposure is associated with epigenetic dysregulation, and that changes in the epigenome may mediate the association between As exposure and adverse health effects. Findings from the research presented here may help inform public health interventions to reduce the adverse health effects of chronic As exposure. However, further research is needed to fully understand the biological mechanism that influence As methylation and that underlie the associations between chronic As exposure and adverse health outcomes.

Arsenic is a toxic element that is widely distributed throughout the earth??s crust as a result of both natural geologic processes and anthropogenic activities. In virtually all environments, methylated forms of arsenic can be found. Because of the widespread distribution and toxicity of arsenic and methyl-arsenic, their adsorption behavior on soil minerals is of great interest. Although considerable attention has been given to the behavior of inorganic arsenic on mineral surfaces, little research has been conducted regarding interactions of the methyl-arsenic forms. The objective of this study was to compare the adsorption and desorption behavior of methylarsonate (MMAsV), methylarsonous acid (MMAsIII), dimethylarsinate (DMAsV), dimethylarsinous acid (DMAsIII), arsenate (iAsV), and arsenite (iAsIII) on iron oxide minerals (goethite and ferrihydrite) by means of adsorption isotherms and adsorption envelopes. Additionally, desorption envelopes were obtained using sulfate and phosphate as competitive ligands. Arsenic was measured by FI-HG-AAS. MMAsV and iAsV were adsorbed in higher amounts than DMAsV on goethite and ferrihydrite at all pH values studied. Although MMAsV and iAsV were adsorbed quantitatively at lower concentrations on goethite and ferrihydrite, as arsenic concentration was increased MMAsV was adsorbed in slightly lower quantities than iAsV. DMAsV was not quantitatively adsorbed at any concentration on goethite or ferrihydrite. MMAsV and iAsV exhibited high adsorption affinities on both goethite and ferrihydrite at pH values below 9 and showed decreasing adsorption above this point (more rapidly for MMAsV). DMAsV was adsorbed only at pH values below 8 on ferrihydrite and below 7 on goethite. MMAsV, iAsV, and DMAsV each exhibited adsorption characteristics suggesting specific adsorption on both goethite and ferrihydrite. Increased methyl substitution resulted in increased ease of arsenic release from the iron oxide surface. MMAsIII and DMAsIII exhibited no evidence for any type of specific adsorption under the conditions studied. Phosphate was a more effective desorbing ion than sulfate, but neither desorbed all arsenic species quantitatively.

The objective of this research was to investigate the retention of arsenate (iAsV), arsenite (iAsIII), monomethyl arsenate (MMAsV) and dimethyl arsenate (DMAsV) by calcite and assess the impact of dissolved Ca2+, Mg2+, phosphate and sulfate on arsenic solubility, adsorption and precipitation phenomena. Adsorption kinetics of iAsV, evaluated at a low and high concentration, was a relatively rapid process, with a fast initial reaction rate within the first few minutes and a subsequent slower reaction rate as equilibrium was approached. The relative adsorption of arsenicals decreased in the following order: iAsV > iAsIII > DMAV > MMAV. In no case was a clear adsorption maximum observed with increasing dissolved arsenic concentration. Dissolved 0.01 M Ca2+ resulted in an increase in iAsV adsorption; however, in the presence of 0.1 M Ca2+ adsorption of iAsV was decreased. The presence of Mg2+ as 0.01 M Mg(NO3)2 resulted in decreased iAsV adsorption probably the result of a lower iAsV affinity for adsorbed Mg2+ as compared to Ca2+. Phosphate and sulfate were highly competitive with iAsV in adsorption to calcite and both resulted in decreased iAsV adsorption. The total prevention of iAsV adsorption at initial equimolar arsenic/phosphate concentrations > 88 µM each could be from the consumption of available calcite surface sites by the specific adsorption of phosphate. Equilibrium modeling, using the geochemical and mineral speciation of equilibrium model (MINTEQA2), indicated that at low concentrations of arsenate or phosphate solid-phase precipitation was not likely and adsorption processes likely controlled solubility. At high concentrations of arsenate Ca3(AsO4)2 · 3 2/3 H2O and Ca3(AsO4)2 · 4 1/4 H2O solid phases could be controlling arsenate solubility. This study indicates that arsenic adsorption response by calcite was different than that of phosphate suggesting that arsenic may not be specifically adsorbed to calcium at the calcite surface. Reduction and biomethylation of arsenic decreased adsorption, suggesting that processes which could affect the speciation of arsenic in the environment, could increase arsenic mobility in environmental systems where calcite and dissolved aqueous calcium play a predominant role in controlling arsenic solubility. Dissolved aqueous concentrations of magnesium, phosphate and sulfate generally reduced the ability of arsenic to be adsorbed to calcite.

Arsenic is found in drinking waters in many countries and since maximum allowable concentration is as low as 10 &micro / g/L, there are many research efforts to separate it from water. Membrane methods are used more and more widely in separation operations in recent years. Arsenic is mainly present in water as arsenite [As(III)] and arsenate [As(V)]. As pH of water changes, molecular formulas of As(III) and As(V) change. In this study, the performance of different ultrafiltration membranes for arsenic removal from water was investigated at different pH values, different feed concentrations and presence of other anions (SO42-, HPO42-, NO3-, Cl-). Donnan exclusion effect on separation was discussed since distribution of arsenite and arsenate anions change in water due to change in pH of the solution. Experiments were conducted via batch and continuous modes. For continuous ultrafiltration experiments, 30 kDa of polysulfone and 20 kDa of polyether sulfone membranes were used. Batch ultrafiltration experiments were performed with the usage of 3 kDa of regenerated cellulose membrane. Higher retention values for As(V) were obtained compared to retention values of As(III). When membranes&rsquo / performances were investigated, it was seen that highest As(V) removal was observed with the usage of polysulfone membrane. Increase in feed concentration and presence of other anions caused decrement in separation. Hydride Generation Atomic Absorption Spectrometry was used to perform analyses. Hydride generator part was designed, constructed and optimized to obtain reliable and accurate absorbance values.

Arsenic is a toxic element that is widely distributed throughout the earth??s crust as a result of both natural geologic processes and anthropogenic activities. In virtually all environments, methylated forms of arsenic can be found. Because of the widespread distribution and toxicity of arsenic and methyl-arsenic, their adsorption behavior on soil minerals is of great interest. Although considerable attention has been given to the behavior of inorganic arsenic on mineral surfaces, little research has been conducted regarding interactions of the methyl-arsenic forms. The objective of this study was to compare the adsorption and desorption behavior of methylarsonate (MMAsV), methylarsonous acid (MMAsIII), dimethylarsinate (DMAsV), dimethylarsinous acid (DMAsIII), arsenate (iAsV), and arsenite (iAsIII) on iron oxide minerals (goethite and ferrihydrite) by means of adsorption isotherms and adsorption envelopes. Additionally, desorption envelopes were obtained using sulfate and phosphate as competitive ligands. Arsenic was measured by FI-HG-AAS. MMAsV and iAsV were adsorbed in higher amounts than DMAsV on goethite and ferrihydrite at all pH values studied. Although MMAsV and iAsV were adsorbed quantitatively at lower concentrations on goethite and ferrihydrite, as arsenic concentration was increased MMAsV was adsorbed in slightly lower quantities than iAsV. DMAsV was not quantitatively adsorbed at any concentration on goethite or ferrihydrite. MMAsV and iAsV exhibited high adsorption affinities on both goethite and ferrihydrite at pH values below 9 and showed decreasing adsorption above this point (more rapidly for MMAsV). DMAsV was adsorbed only at pH values below 8 on ferrihydrite and below 7 on goethite. MMAsV, iAsV, and DMAsV each exhibited adsorption characteristics suggesting specific adsorption on both goethite and ferrihydrite. Increased methyl substitution resulted in increased ease of arsenic release from the iron oxide surface. MMAsIII and DMAsIII exhibited no evidence for any type of specific adsorption under the conditions studied. Phosphate was a more effective desorbing ion than sulfate, but neither desorbed all arsenic species quantitatively.

One of the most toxic environmentally mobile compounds found in water is arsenic. It has been used as a pesticide to control insects, fungi, weeds and rodents since the early part of this century because of its high toxicity. Sorption of toxic metals onto a metal oxy-hydroxide is the most popular and practical arsenic removal method from contaminated water. Water treatment with oxy-hydroxides creates arsenic containing residuals, which are usually disposed of in landfills. To prevent leaching, stabilization of the solid residuals is required. It has been reported that calcium may inhibit arsenic desorption and/or benefit arsenic sorption. The objective of this investigation is to assess arsenic leaching in the presence of calcium and phosphate ions at extreme pH. Two hypotheses have been identified to explain the decrease in soluble arsenic in the presence of calcium. One explanation is that arsenic reacts with calcium to form calcium arsenic solids. The second hypothesis is that calcium affects the surface properties of the oxy-hydroxide solid in solution. Results show that calcium enhances the removal by iron oxides and prevents the leaching of arsenic from the residuals. Isotherm experiments show that arsenic adsorption can be described as occurring on nonporous powders or powders with pore diameters larger than micro-pores. Physically, with increase in adsorbate concentration, second and more layers are completed until saturation when the numbers of adsorbed layers becomes infinite. Further, experimental data were fitted to a Brunauer, Emmett and Teller isotherm (BET) model which assumes the initial layer can act as substrate for further adsorption. Finally, calcium-arsenic and calcium-phosphate solids were predicted to be formed by Visual MINTEQ modeling program. Nevertheless, from the x-ray diffraction output calcium-arsenic or calcium-phosphate solids were not identified. Because no calcium arsenate solids were found it was concluded that calcium affects the surface properties of the oxy-hydroxide solids in solution. Increasing the pH produces negative surface charge, which in turn increases repulsion between the negatively charged hydrated arsenate ions and the Fe(OH)3 surface. Calcium’s positive charge might neutralize this effect enhancing the sorption of arsenic onto the oxy-hydroxide. Also, it was concluded that the competition between arsenic and phosphate was reduced by the same mechanisms.