This study examines the natural background concentrations of arsenic in the soils of southwest Oregon, using new samples in addition to data collected from previous theses (Khandoker, 1997 and Douglas, 1999). The original 213 samples were run by ICP-AES with a reporting limit of 20 ppm, and only three samples had detected values. The original samples were tested again (2013) at a lower reporting limit of 0.2 ppm by ICP-MS, as were 42 new samples (2013), to better ascertain the natural levels of arsenic in undisturbed soils. The aim is to add to the existing DEQ data set, which has been used to establish new regulatory levels based on natural levels in the environment that are both safer and more economically viable than the former risk-based remediation levels (DEQ, 2013). The maximum and mean concentrations, respectively, for each province (with high formation map unit) are 85.4 and 21.99 ppm for South Willamette Valley (Tfee), 45.4 and 5.42 ppm for the Klamath Mountains (Jub), 11.9 and 2.76 ppm for the Cascade Range (Tbaa), 10.6 and 5.15 ppm for the Coast Range (Ty), 2.32 and 1.29 ppm for the Basin and Range (Qba) and 1.5 and 1.20 ppm for the High Lava Plains (Tmv). In addition, the distribution and variance of arsenic in the A and B soil horizons is assessed in this study by comparing deviation at a single site, and also by comparing A and B horizons of 119 PSU sites. One of 18 new sites sampled for this study (distinguished with the HH prefix), site HH11, was randomly chosen to evaluate differences at a single location. Site HH11 is an Inceptisol soil above volcanic rock (KJdv map unit) located at 275 meters elevation in Douglas County within the Klamath province. Five samples were taken from the A and from the B horizons at site HH11. The means and standard deviations were 3.74 ± 0.44 for the A horizon and 4.53 ± 0.39 for the B horizon. The consistency and low deviation within each horizon indicate that a single sample within a horizon is a good representative of that horizon and supports the field methodology used in this study of taking only one sample in the A horizon and one sample in the B horizon. Wilcoxon Rank-Sum test determined that A and B horizons for the 119 sites that had data for both the A and B horizons were not statistically different (p-value 0.76). Arsenic concentration is not associated with a particular horizon for these sites. However, differentiation between soil horizons increases with age (Birkeland, 1999), as does accumulation of the iron oxides and sulfide minerals on clay surfaces (McLaren et al., 2006) which concentrate in the B horizon. These associations warrant further study to see how they relate to arsenic level, soil development and age in Oregon soils. Lastly, this study statistically examines six potentially important environmental predictors of naturally occurring arsenic in southwestern Oregon: site elevation, geomorphic province, mapped rock type and age, and sample soil order and color (redness). A Classification and Regression Tree Model (CART) determined soil order, elevation and rock type to be of significant importance in determining arsenic concentrations in the natural environment. According to the regression tree, arsenic concentrations are greater within Alfisol and Ultisol/Alfisol and Vertisol soil orders, at lower elevations below 1,207 meters, and within soils from sedimentary, mixed volcanic/sedimentary and unconsolidated rock types.

Volcanic tuffs and tuffaceous sediments are frequently associated with elevated As groundwater concentrations even though their bulk As contents (~ 5 mg kg-1; Savoie, 2013) are only marginally greater than the average crustal abundance of 4.8 mg g-1 (Rudnick & Gao, 2003). Thus, As mobilization must be facilitated by conditions particular to these rocks. Alkaline desorption, anionic competition, reactive glass dissolution, and reductive dissolution of iron oxides are proposed processes of As release from volcanic rocks. Geogenic As contamination of groundwater in the southern Willamette Valley in western Oregon has been well-documented since the early 1960s, and previous studies have identified the Little Butte Volcanics Series and Fisher and Eugene Formations as the source of As contamination. This study examines 19 samples from 10 units of ash flow tuffs and tuffaceous sediments within the Fisher Formation and Little Butte Volcanics Series, representing a range of weathering and devitrification, to determine conditions of mobilization and mineralogical constraints that control As release into solution. Leachate studies were conducted over a range of pH from 7 to 11, phosphate concentrations from 10 μM to 100 mM, and in time series from 4 to 196 hours. Results demonstrate that silicic volcanic tuffs are capable of mobilizing As in concentrations above regulatory limits at pH conditions produced naturally by the tuffs (pH 8-9) or with moderate concentrations of P (10-100 μM). Alteration products, e.g. zeolites and clays, appear to be the primary host phases for mobile As. Samples that do not contain these alteration products tend to produce concentrations of As well below regulatory limits and often below the instrument detection limits of this study. The type of alteration may influence As mobilization: tuffs containing more clays tend to mobilize As through surficial desorption, and tuffs containing more zeolites tend to mobilize As by dissolution or formation of colloids. Additionally, one volcaniclastic sample demonstrates that extremely elevated concentrations of As, up to 1000 μg/L are possible as a result of oxidative dissolution of As-bearing sulfide phases.

Groundwater arsenic contamination is currently a global problem, and also a concern at numerous former industrial sites, agricultural sites, landfill sites and mining operations in the U.S. This dissertation aims to develop improved strategies of remediating these arsenic contaminated aquifers. It focuses on two distinct approaches of remediation: (1) mobilizing arsenic from contaminated aquifer sediments to decrease the quantity of arsenic at the source of contamination; and (2) immobilizing arsenic in situ, to decrease the mobility and bioavailability of this arsenic. Optimal remediation may well involve combinations of these two approaches. Arsenic mobilization using oxalic acid is effective because oxalic acid dissolves arsenic host minerals and competes for sorption sites on those minerals. In this dissertation, oxalic acid treatment was tested using sediments with contrasting iron mineralogies and arsenic contents from the Dover Municipal Landfill and the Vineland Chemical Company Superfund sites. Oxalic acid mobilized arsenic from both sites and the residual sediment arsenic was less vulnerable to microbial reduction than before the treatment. Oxalic acid thus could improve the efficiency of widely used pump-and-treat remediation. Oxalic acid did not remove all of the reactive iron(III) minerals in Vineland sediment samples, and thus released significant quantities of arsenic into solution under reducing conditions than the Dover samples. Therefore, the efficacy of pump-and-treat must consider iron mineralogy when evaluating its overall potential for remediating groundwater arsenic. Arsenic immobilization occurs by changing the chemical state, or speciation, of arsenic and other elements in the system. Arsenic is often assumed to be immobile in sulfidic environments. In this dissertation, sulfate reduction was stimulated in sediments from the Vineland Superfund site and the Coeur d'Alene mining district. Sulfate reduction in the Coeur d'Alene sediments was more effective at removing arsenic from solution than the Vineland sediments. The Vineland sediments initially contained abundant reactive ferrihydrite, and underwent extensive sulfur cycling during incubation. As a result, arsenic in the Vineland sediments could not be effectively converted to immobile arsenic-bearing sulfides, but instead a part of the arsenic was probably converted to soluble thioarsenates. Therefore, coupling between the iron and sulfur redox cycles must be fully understood for arsenic immobilization by sulfate reduction to be successful. Arsenic can also be immobilized by retention on magnetite (Fe3O4). Magnetite is stable under a wide range of aquifer conditions including both oxic and iron(III)-reducing environments. In this dissertation, a series of experiments were performed with sediments from the Dover and Vineland Superfund sites, to examine the potential of magnetite for use in arsenic immobilization. Our data suggest that the formation of magnetite can be achieved by the microbial oxidation of ferrous iron with nitrate. Magnetite can incorporate arsenic into its structure during formation, forming a stable arsenic sink. Magnetite, once formed, can also immobilize arsenic by surface adsorption, and thus serve as a reactive filter when contaminated groundwater migrates through the treatment zone. Reactive transport modeling is used for investigating the magnetite based arsenic immobilization strategy and for scaling laboratory results to field environments. Such modeling suggests that the ratio between iron(II) and nitrate in the injectant regulates the formations of magnetite and ferrihydrite, and thus regulates the long-term evolution of the effectiveness of the strategy. The results from field-scale models favor scenarios that rely on the chromatographic mixing of iron(II) and nitrate after injection. The studies in this dissertation demonstrate that the environmental fate of arsenic depends on the biogeochemical cycling of arsenic, iron, and to a lesser extent, sulfur. The development of effective groundwater arsenic remediation strategies depends on a good understanding of each of the involved processes, and their combinations.

This dissertation discusses three questions of development and environmental economics. First, it assesses the impact of mineral mining on the health and wealth of households in local communities across 44 developing countries, using micro data. Secondly, it presents evidence from a randomized controlled trial on the cost-shared provision of well-water tests for arsenic. Finally, it analyzes measurement error in a satellite night light data product widely used in development research, and investigates the scope for using the data in very high spatial resolution.

This project examines arsenic in plants growing near closed or reclaimed gold mines located in the traditional territories of two Yukon First Nations. A total of 238 soil and plant samples (comprising 9 different species) were collected from Mt. Nansen, Arctic Gold and Silver, and Venus Mine tailing properties. At each property, samples were collected near the suspected point source of contamination, approximately 1 -3 km away, and from background sites. Species were chosen for their ethnobotanical significance to the Little Salmon/Carmacks and the Carcross/Tagish First Nations, based on interviews with Elders and other knowledgeable people. Total and inorganic arsenic concentrations were determined using ICP-MS and AAS instrumentation, and organic arsenic concentrations were calculated from the difference. Uptake of arsenic by plants was low compared to soil arsenic concentrations. In both plants and soil, the arsenic form was predominantly inorganic. Concentrations in berries at all three sites were low or undetectable, and are therefore considered safe to eat under Health Canada tolerable daily intake guidelines for inorganic arsenic. At Mt. Nansen, the lichen "caribou moss" (Cetraria/Cladina spp.), Bolete mushrooms (Leccinum spp.), and the medicinal shrubs willow (Salix spp.) and Labrador tea (Ledum groenlandicum/L. decumbens spp.) had high mean arsenic concentrations around point sources or at sites up to 1.5 km away. These localized high concentrations will not likely affect foraging animals, given their constant movement. However, Carmacks residents could avoid gathering all species with elevated arsenic around the Mt. Nansen mining property until reclamation is complete.

This project examines arsenic in plants growing near closed or reclaimed gold mines located in the traditional territories of two Yukon First Nations. A total of 238 soil and plant samples (comprising 9 different species) were collected from Mt. Nansen, Arctic Gold and Silver, and Venus Mine tailing properties. At each property, samples were collected near the suspected point source of contamination, approximately 1 -3 km away, and from background sites. Species were chosen for their ethnobotanical significance to the Little Salmon/Carmacks and the Carcross/Tagish First Nations, based on interviews with Elders and other knowledgeable people. Total and inorganic arsenic concentrations were determined using ICP-MS and AAS instrumentation, and organic arsenic concentrations were calculated from the difference. Uptake of arsenic by plants was low compared to soil arsenic concentrations. In both plants and soil, the arsenic form was predominantly inorganic. Concentrations in berries at all three sites were low or undetectable, and are therefore considered safe to eat under Health Canada tolerable daily intake guidelines for inorganic arsenic. At Mt. Nansen, the lichen "caribou moss" (Cetraria/Cladina spp.), Bolete mushrooms (Leccinum spp.), and the medicinal shrubs willow (Salix spp.) and Labrador tea (Ledum groenlandicum/L. decumbens spp.) had high mean arsenic concentrations around point sources or at sites up to 1.5 km away. These localized high concentrations will not likely affect foraging animals, given their constant movement. However, Carmacks residents could avoid gathering all species with elevated arsenic around the Mt. Nansen mining property until reclamation is complete. / Arts, Faculty of / Geography, Department of / Graduate

Reducing population exposure to inorganic arsenic (iAs), a known carcinogen and highly toxic metalloid of great public health concern, remains an ongoing challenge worldwide and in the United States (US). In the US, the Environmental Protection Agency (EPA) regulates the maximum contaminant level (MCL) for total arsenic in public drinking water supplies through the Safe Drinking Water Act. In 2001, the US EPA implemented the Final Arsenic Rule, which lowered the MCL for arsenic in public drinking water supplies from 50 to 10 µg/L. Reductions in iAs exposure and subsequent related disease associated with this important regulatory change have not been quantified. Currently, no national-level exposure estimates of iAs drinking water exposure are available for US residents reliant on public drinking water. There is a critical need to identify susceptible subgroups of the US population who remain at risk for elevated iAs drinking water exposure. This dissertation aimed to quantify the reduction in drinking water iAs exposure resulting from the US EPA MCL regulatory change, to estimate drinking water iAs exposure for US residents reliant on public drinking water, to identify susceptible subgroups across the US whose water iAs remains high, and to determine if iAs exposure was associated with heart disease mortality in the general US population. Chapter 1 provides background information necessary to contextualize the work contained in this dissertation. In Chapter 2, we conducted a cross-sectional analysis of dietary sources of iAs exposure in the Strong Heart Family Study, a cohort of American Indian adults followed primarily for cardiovascular disease, using a self-reported food frequency questionnaire and urinary iAs measurements. Self-reported intake of rice, organ meat, processed meat, and non-alcoholic drinks was associated with increased urinary iAs concentrations. Diet alone explained only 3% of total variability in urinary iAs concentrations, indicating that the majority of iAs exposure for SHFS participants occurs from drinking water. Second, (in Chapter 3), we explored trends in water iAs exposure in the general US population associated with the EPA’s MCL change using the National Health and Nutrition Examination Survey (NHANES) from 2003-2014, separately for participants reliant on public drinking water vs. private well water (which is not subject to US EPA regulation). We estimated that implementation of the new US EPA MCL was associated with a 17% reduction in drinking water iAs exposure for all participants reliant on public drinking water; the corresponding reduction was 32% for Mexican-American participants. No reduction was observed for participants reliant on private wells. Third (in Chapter 4), we estimated drinking water iAs exposure at the community water system and county-level across the entire US from 2006-2011 using the US EPA’s Six Year Review of Contaminant Occurrence database. We estimated that nationwide public drinking water iAs concentrations decreased by 8.5% and 21.6% at the 80th and 99th percentiles of the water iAs distribution in accordance with the MCL implementation, with significant differences across US subgroups. Greater decreases in iAs concentrations were reported for systems reliant on groundwater, systems serving smaller populations, and systems in the Northeast, Central Midwest, and Southwestern regions of the US. Susceptible subgroups whose public drinking water iAs exposure remains high include populations served by small community water systems reliant on groundwater, communities in the Southwestern US, Semi-Urban, Hispanic communities, and Rural, American Indian communities. Fourth (in Chapter 5), we assessed six-year average arsenic concentrations in community water systems exclusively serving correctional facilities in the US (e.g. prisons, jails, detention centers) compared to other community water systems. Average arsenic concentrations were twice as high in correctional facility community water systems located in the Southwest (6.41 µg/L, 95% CI 3.48, 9.34) compared to all other community water systems in the Southwest (3.11 µg/L, 95% CI 2.97, 3.24). Over a quarter of correctional facility systems in the Southwest reported a six-year average arsenic concentration exceeding the 10 µg/L MCL. Persons incarcerated in the Southwestern US were at disproportionate risk of drinking water arsenic exposure and related disease from 2006-2011. Fifth (in Chapter 6), we multiply imputed urinary arsenic concentrations below the limit of detection (LOD) in NHANES 2003-2016 using a Bayesian Tobit regression model. Epidemiological analyses of urinary arsenic data in NHANES are limited by the relatively high analytical LODs and large proportion of participants with undetectable values. Distributions of urinary arsenic originally reported in NHANES, which replace values below the LOD with the LOD divided by the square root of two, likely overestimate iAs exposure at the lowest exposure levels and may introduce significant bias. Bayesian-multiply imputed datasets may improve the assessment of iAs exposure in cohorts with high analytical LODs for arsenic species. Finally (in Chapter 7), we evaluated the association between urinary iAs concentrations (internal dose) and heart disease mortality as recorded in the National Death Index in NHANES 2003-2014 participants. We found a positive but non-significant prospective association between increasing iAs exposure and heart disease mortality for all participants (hazard ratio 1.15, 95% CI 0.77, 1.70), and a significant positive association for non-Hispanic white participants using flexible spline models. Geometric mean ratios of iAs exposure were higher among cases compared to non-cases, especially for Mexican-American participants (1.30, 95% CI 0.90, 1.88). These findings further support the potential association between low- to moderate- iAs exposure and cardiovascular disease in the US population, and indicate that further high-quality prospective studies of Hispanic and Latino Americans are needed to investigate the potential increased susceptibility of Mexican-Americans to iAs-related cardiovascular disease. Taken together, these studies suggest that while the implementation of the US EPA’s 10 µg/L MCL has reduced drinking water arsenic exposure for many Americans reliant on public drinking water systems, these reductions were not uniform across all US populations. Populations who remain at risk of elevated drinking water arsenic exposure include those reliant on domestic wells, those located in the Southwest, persons incarcerated in the Southwest, tribal communities, and Hispanic communities. Further high-quality epidemiologic research is needed to evaluate the association between low- to moderate iAs exposure and cardiovascular disease in these populations. Stronger federal regulations, targeted compliance enforcement and technical assistance, and other public health interventions are needed to reduce drinking water arsenic exposure in these communities.

Inorganic arsenic is a potent carcinogen and toxicant associated with numerous adverse health outcomes, and is number one on the Agency for Toxic Substances and Disease Registry Substance Priority List. Uranium is also a carcinogen and nephrotoxicant, however health effects at levels experienced by general populations is unclear. Chronic exposure to inorganic arsenic (As) and uranium (U) in the United States (US) occurs from unregulated private wells and federally regulated community water systems (CWSs). Geogenic arsenic contamination typically occurs in groundwater as opposed to surface water supplies. Groundwater is a major source for many CWSs in the US. Although the US Environmental Protection Agency sets the maximum contaminant level (MCL enforceable since 2006: 10 µg/L) for arsenic in CWSs, private wells are not federally regulated. The contribution of drinking water from private wells and regulated CWSs to total inorganic arsenic and uranium exposure is not clear.In the United States (US), type 2 diabetes (T2D) affects approximately 37.3 million people (11.3% of the population), with the highest burden in American Indian communities. Toxic metal exposures have been identified as risk factors of T2D. Most studies rely on biomarkers, which could be affected by early disease processes. Studies directly measuring metals in drinking water in US populations have been limited. In Chapter 2, we evaluated county-level associations between modeled values of the probability of private well arsenic exceeding 10 µg/L and CWS arsenic concentrations for 2,231 counties in the conterminous US, using time invariant private well arsenic estimates and CWS arsenic estimates for two time periods. Nationwide, county-level CWS arsenic concentrations increased by 8.4 µg/L per 100% increase in the probability of private well arsenic exceeding 10 µg/L for 2006 – 2008 (the initial compliance monitoring period after MCL implementation), and by 7.3 µg/L for 2009 – 2011 (the second monitoring period following MCL implementation) (1.1 µg/L mean decline over time). Regional differences in this temporal decline suggest that interventions to implement the MCL were more pronounced in regions served primarily by groundwater. The strong association between private well and CWS arsenic in Rural, American Indian, and Semi Urban, Hispanic counties suggests that future research and regulatory support are needed to reduce water arsenic exposures in these vulnerable subpopulations. This comparison of arsenic exposure values from major private and public drinking water sources nationwide is critical to future assessments of drinking water arsenic exposure and health outcomes. In Chapter 3, we aimed to determine the association between drinking water arsenic estimates and urinary arsenic concentrations in the 2003-2014 National Health and Nutrition Examination Survey (NHANES). We evaluated 11,088 participants from the 2003-2014 NHANES cycles. For each participant, we assigned private well and CWS arsenic levels according to county of residence using estimates previously derived by the U.S. Environmental Protection Agency and U.S. Geological Survey. We used recalibrated urinary dimethylarsinate (rDMA) to reflect the internal dose of estimated water arsenic by applying a previously validated, residual-based method that removes the contribution of dietary arsenic sources. We compared the adjusted geometric mean ratios and corresponding percent change of urinary rDMA across tertiles of private well and CWS arsenic levels, with the lowest tertile as the reference. Comparisons were made overall and stratified by census region and race/ethnicity. Overall, the geometric mean of urinary rDMA was 2.52 (2.30, 2.77) µg/L among private well users and 2.64 (2.57, 2.72) µg/L among CWS users. Urinary rDMA was highest among participants in the West and South, and among Mexican American, Other Hispanic, and Non-Hispanic Other participants. Urinary rDMA levels were 25% (95% confidence interval (CI): 17-34%) and 20% (95% CI: 12-29%) higher comparing the highest to the lowest tertile of CWS and private well arsenic, respectively. The strongest associations between water arsenic and urinary rDMA were observed among participants in the South, West, and among Mexican American and Non-Hispanic White and Black participants. Both private wells and regulated CWSs are associated with inorganic arsenic internal dose as reflected in urine in the general U.S. population. In Chapter 4, our objective was to evaluate regional and sociodemographic inequalities in water arsenic exposure reductions associated with the US Environmental Protection Agency’s Final Arsenic Rule, which lowered the arsenic maximum contaminant level to 10 µg/L in public water systems. We analyzed 8,544 participants from the 2003-14 National Health and Nutrition Examination Survey (NHANES) reliant on community water systems (CWSs). We estimated arsenic exposure from water by recalibrating urinary dimethylarsinate (rDMA) to remove smoking and dietary contributions. We evaluated mean differences and corresponding percent reductions of urinary rDMA comparing subsequent survey cycles to 2003-04 (baseline), stratified by region, race/ethnicity, educational attainment, and tertile of CWS arsenic assigned at the county level. The overall difference (percent reduction) in urine rDMA was 0.32 µg/L (9%) among participants with the highest tertile of CWS arsenic, comparing 2013-14 to 2003-04. Declines in urinary rDMA were largest in regions with the highest water arsenic: the South [0.57 µg/L (16%)] and West [0.46 µg/L, (14%)]. Declines in urinary rDMA levels were significant and largest among Mexican American [0.99 µg/L (26%)] and Non-Hispanic White [0.25 µg/L (10%)] participants. Reductions in rDMA following the Final Arsenic Rule were highest among participants with the highest CWS arsenic concentrations, supporting legislation can benefit those who need it the most, although additional efforts are still needed to address remaining inequalities in CWS arsenic exposure. In Chapter 5, we examined the contribution of water As and U to urinary biomarkers in the Strong Heart Family Study (SHFS), a prospective study of American Indian communities, and the Multi-Ethnic Study of Atherosclerosis (MESA), a prospective study of racially/ethnically diverse urban US communities. We assigned residential zip code-level estimates in CWSs (µg/L) and private wells (90th percentile probability of As >10 µg/L) to up to 1,485 and 6,722 participants with dietary information and urinary biomarkers in the SHFS (2001-2003) and MESA (2000-2002; 2010-2011), respectively. Total inorganic As exposure was estimated as the sum of inorganic and methylated species in urine (urine As). We used linear mixed-effects models to account for participant clustering and removed the effect of dietary sources of As and U via regression adjustment. The median (interquartile range) urine As was 5.32 (3.29, 8.53) and 6.32 (3.34, 12.48) µg/L for SHFS and MESA, respectively, and urine U was 0.037 (0.014, 0.071) and 0.007 (0.003, 0.018) µg/L. In a mixed-effects meta-analysis of pooled effects across the SHFS and MESA, urine As was 11% (95% CI: 3, 20%) higher and urine U was 35% (5, 73%) higher per 2-fold higher CWS As and U, respectively. In the SHFS, CWS and private well As explained >40% of variability in urine As and CWS U explained >20% of urine U. In MESA, CWS As and U explained >50% of urine As and U. Water from public water supplies and private wells represents a major contributor to inorganic As and U exposure in diverse US populations. In Chapter 6, we examined the association of arsenic exposures in community water systems (CWS) and private wells with T2D incidence in the Strong Heart Family Study (SHFS), a prospective cohort of American Indian communities, and the Multi-Ethnic Study of Atherosclerosis (MESA), a prospective study of racially/ethnically diverse urban US communities, to evaluate direct associations between drinking water metal exposures and T2D risk. We evaluated adults in the SHFS free of T2D at baseline (2001-2003) and followed through 2010, with available private well and CWS arsenic (N=1,791) estimates assigned by residential zip code. We also evaluated adults in the MESA free of T2D at baseline (2000-2002) and followed through 2019, with available zip code level CWS arsenic (N=5,577) estimates. We used mixed effects Cox models to account for clustering by family and residential zip code, with adjustment for sex, baseline age, body mass index (BMI), smoking status, and education. T2D incidence in the SHFS was 24.4 cases per 1,000 people (mean follow-up 5.6 years) and T2D incidence in MESA was 11.2 per 1,000 people (mean follow-up 6.0 years). In a meta-analysis of pooled effects across the SHFS and MESA, the corresponding hazard ratio (95% confidence interval) per 2-fold increase in water arsenic was 1.09 (1.01, 1.16). Differences were observed by BMI category and sex; positive associations were observed among participants with BMI <25 kg/m2 and among female participants. In categorical analyses, >10% probability of private well arsenic (<10% reference) in the SHFS and >1 µg/L of CWS arsenic (<1 µg/L reference) in MESA were associated with increased diabetes risk. Low to moderate water arsenic levels in unregulated private wells and federally regulated CWSs were associated with T2D incidence in the SHFS and MESA. In supplementary analyses, we also observed that CWS uranium was associated with T2D risk among SHFS and MESA participants with BMI<25 kg/m2.

PhD (Environmental Sciences) / Department of Ecology and Resource Management / The presence of arsenic in groundwater has drawn worldwide attention from researchers and public health officials due to its effects on human health such as, cancer, skin thickening, neurological disorders, muscular weakness, loss of appetite and nausea. World Health Organisation (WHO) has set the limit of 10 μg/L for arsenic in drinking water in trying to reduce the effects of arsenic. This was further adopted by South African National Standard (SANS). The present study aims at evaluating arsenic concentration in selected groundwater sources around Greater Giyani Municipality in Limpopo Province and further synthesize clay based adsorbents for arsenic removal using Fe3+ and Mn2+ oxides and hexadecylammonium bromide (HDTMA-Br) cationic surfactant as modifying agents. The first section of the work presented the hydrogeochemical characteristics of groundwater in the Greater Giyani Municipality. The results showed that the pH of the samples ranges from neutral to weakly alkaline. The dominance of major anionic and cationic species was found to be in the order: HCO3 ->Cl->SO4 2->NO3 - and Na+>Mg2+>Ca2+>K+>Si4+, respectively. Hydrogeochemical facies identified in the study area include CaHCO3 (90%) and mixed CaNaHCO3 (10%) which shows the dominance of water-rock interaction. About 60% of the tested samples contains arsenic concentration above 10 μg/L as recommended by SANS and WHO. Concentration of arsenic was found to be ranging between 0.1 to 172.53 μg/L with the average of 32.21 μg/L. In the second part of this work, arsenic removal efficiency of locally available smectite rich and kaolin clay was evaluated. Results showed that the percentage As(V) removal by kaolin clay was optimum at pH 2 while the percentage As(III) removal was greater than 60% at pH 2 to 12. For smectite rich clay soils, the percentage of As(III) and As(V) removal was found to be optimum at pH between 6 and 8. The adsorption isotherm data for As(III) and As(V) removal by both clays fitted better to Freundlich isotherm. Adsorption of both species of arsenic onto the clay mineral occurred via electrostatic attraction and ion exchange mechanisms. Both clay soils could be regenerated twice using Na2CO3 as a regenerant. Kaolin clay showed a better performance and was selected for further modification. In the third section of this work, Fe-Mn bimetal oxide modified kaolin clay was successfully synthesized by precipitating Fe3+ and Mn2+ metal oxides to the interlayer surface of kaolin clay. Modification of kaolin clay increased the surface area from 19.2 m2/g to 29.8 m2/g and further v decreased the pore diameter from 9.54 to 8.5 nm. The adsorption data fitted to the pseudo second order of reaction kinetics indicating that adsorption of As(III) and As(V) occurred via chemisorption. The adsorption isotherm data was described by Langmuir isotherm models showing a maximum As(III) and As(V) adsorption capacities of 2.16 and 1.56 mg/g, respectively at a temperature of 289 K. Synthesized adsorbent was successfully reused for 6 adsorptiondesorption cycles using K2SO4 as a regenerant. Column experiments showed that maximum breakthrough volume of ≈2 L could be treated after 6 hours using 5 g adsorbent dosage. Furthermore, the concentration of Fe and Mn were within the WHO permissible limit. In the fourth part of the work kaolin clay was functionalized with hexadecyltrimethylamonium bromide (HDTMA-Br) cationic surfactant and its application in arsenic removal from groundwater was investigated. The results revealed that adsorption of As(III) and As(V) is optimum at pH range 4-8. The maximum As(III) and As(V) adsorption capacities were found 2.33 and 2.88 mg/g, respectively after 60 min contact time. Pseudo first order model of reaction kinetics described the adsorption data for As(V) better while pseudo second order model described As(III) adsorption data. The adsorption isotherm data for As(III) and As(V) fitted well to Langmuir model indicating that adsorption of both species occurred on a mono-layered surface. Adsorption thermodynamics model revealed that adsorption of As(III) and As(V) was spontaneous and exothermic. The As(III)/As(V) adsorption mechanism was ascribed to electrostatic attraction and ion exchange. The regeneration study showed that synthesized adsorbent can be used for up to 5 times. In the firth part of the work inorgano-organo modified kaolin clay was successfully synthesized through intercalation of Fe3+ and Mn2+ metal oxides and HDTMA-Br surfactant onto the interlayers of the clay mineral. The batch experiments showed that As(III) removal was optimum at pH range of 4-6, while the As(V) removal was optimum at pH range 4-8. The adsorption data for both species of arsenic showed a better fit to pseudo second order of reaction kinetics which suggest that the dominant mechanism of adsorption was chemisorption. The isotherm studies showed better fit to Langmuir isotherm model as compared to Freundlich model. The maximum adsorption capacity As(III) and As(V) at room temperature as determined by Langmuir model were found to be 7.99 mg/g and 7.32 mg/g, respectively. The thermodynamic studies for sorption of As(III) and As(V) showed negative value of ΔGᴼ and ΔHᴼ indicating that adsorption process occurred spontaneously and is exothermic in nature. The regeneration study showed that the vi inorgano-organo modified kaolin clay can be reused for up 7 adsorption-regeneration cycles using 0.01 M HCl as a regenerant. Thomas kinetic model and Yoon-Nelson model showed that the rate of adsorption increases with increasing flow rate and initial concentration and decreases with increasing of the bed mass. In conclusions, adsorbents synthesized from this work showed a better performance as compared to other adsorbents available in the literature. Among the synthesized adsorbents, inorgano-organo modified clay showed highest adsorption capacity as compared to surfactant functionalized and Fe-Mn bimetal oxides modified kaolin clay. However, all adsorbents were recommended for use in arsenic remediation from groundwater. The following recommendations were made following the findings from this study: 1) routine monitoring of arsenic in groundwater of Greater Giyani Municipality, 2) evaluating the possible link between arsenic exposure and arsenic related diseases within Giyani in order to find the extent of the problem in order to establish the population at risk, 3) The toxicity assessment for HDTMA-Br modified kaolin clay should be carried out, 4) Materials developed in the present study should be modeled and tested at the point of use for arsenic removal, and lastly, 5) this study further encourage the development of other arsenic removal materials that can be used at household level. / NRF