Teses / dissertações sobre o tema "Arsenic Environmental aspects Bangladesh"

Thesis: Ph. D. in Environmental Engineering, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2018.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Naturally-occurring groundwater arsenic can threaten human health and food security. In Bangladesh, >50 million people are estimated to have chronically consumed water with arsenic above the World Health Organization (WHO) guideline of 10 μg/L, which can contribute to cancer, cardiovascular disease, and reproductive and developmental effects. Studies relating arsenic exposure to health impacts generally estimate dose based on participants' primary household wells. Using a mass-balance for arsenic and water, we estimate that participants in Araihazar, Bangladesh obtain 37±8% of their water from primary household wells and 31±14% from other wells, and we thus recommend the inclusion of other wells in dose estimation. Concentrations of arsenic in well water are spatially variable, enabling many exposed households to switch to nearby lower-arsenic wells in response to area-wide well testing. Following well testing and education in Araihazar, arsenic exposure declined and remained lowered for at least eight years. Participants with arsenic-unsafe wells were 6.8 times more likely to switch wells over the first two years and 1.4-1.8 times more likely to switch wells over the ensuing decade. Rice comprises more than 70% of calories consumed in Bangladesh, and rice yield is negatively impacted by the buildup of arsenic in soil from irrigation with high-arsenic water. We investigated the effect of soil arsenic on yield using a controlled study design where we exchanged the top 15 cm of soil between high-arsenic and low-arsenic plots. Differences in yield were negatively correlated to differences in soil arsenic between adjacent soil replacement and control plots, suggesting that boro rice yield countrywide may be diminished by 7-26% due to arsenic in soil. Soil testing and removal of high-arsenic soil may enable farmers to mitigate the impacts of arsenic on rice. Twelve measurements made with the ITS Econo-Quick field kit could be used to estimate whether soil arsenic was above or below a 30 mg/kg intervention threshold with 80-90% accuracy. A soil inversion, where deep low-arsenic soil was exchanged with surface high-arsenic soil, decreased soil arsenic, organic carbon, nitrogen, and phosphorus concentrations by about 40% in the top 20 cm of soil and improved rice yield by 15-30%.
by Brittany Lynn Huhmann.
Ph. D. in Environmental Engineering

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007.
Includes bibliographical references.
Widespread arsenic contamination of groundwater has become a major concern in Bangladesh since the water supply, particularly in rural areas, is heavily dependent on groundwater. However, relative to the extent of research on biogeochemical processes of arsenic mobilization, very little work has been conducted to understand the complex transient dynamics of groundwater flow, and the transport of arsenic and other solutes that control its mobility in the area. A detailed three-dimensional hydrological model of our study area in Munshiganj indicates that: (1) the shallow aquifer acts primarily as a conduit for flow from ponds and rice fields to irrigation wells and rivers; (2) most inflow to the aquifer occurs during the dry season, and monsoon contributes relatively little to the inflow since the aquifer storage is small; (3) since the increase in irrigation pumping and pond construction have changed the groundwater flow dynamics, arsenic concentrations are unlikely to be at steady-state. These observations are consistent with those from the lumped-parameter model. Analysis of various fluxes from the three-dimensional groundwater model also reveals that ponds provide the largest source of recharge to the aquifer, and hence, is a potential source of dissolved arsenic to the subsurface. Accordingly, a "Pond Hypothesis" has been developed suggesting that arsenic mobilization in Bangladesh aquifer is deriving from reductive dissolution of various arsenic bearing oxides (the widely accepted mechanism for arsenic mobilization in Bangladesh) deposited at the pond bottoms. The process of reductive dissolution occurs in the presence of organic matter and under reducing environment, when residing microbes respire on oxygen from oxide-minerals (e.g. Fe and Mn oxides) to process the organic matter for growth, and subsequently causes release of arsenic associated with the oxide-minerals to the aqueous phase.
(cont.) Afterwards, at the end of flooding season, the dissolved arsenic along with mixture of various dissolved solutes from pond bottoms enters the aquifer and is driven towards the well screen both vertically due to overlying recharge and horizontally due to increased pumping. Extensive small-scale pump tests and one large-scale extended pumping experiment carried out at our study area in Munshiganj indicates that the aquifer is anisotropic in nature creating flow convergence at the depth of irrigation well screen. Results from a three-dimensional hydrological model suggests that groundwater irrigation has changed the flow dynamics in the area - not only by reducing the residence and travel times, but also carrying solutes to particular depth from different sources and locations. Model simulations carried out for three different scenarios - 'Current Stage' (if the current flow condition continues), 'Ancient Stage' (before the advent of habitation and irrigation practices), and 'Inception Stage' (the beginning of irrigation and creation of ponds) - indicates that in general, the rice field water dominates at the shallowest depth while pond water dominates at the depth of irrigation well, and the contribution from river water increases with depth. Analysis of the average groundwater age distribution indicates that younger age dominates at shallower depths. More importantly, the age values at the monitoring locations can be explained by the relative contribution of recharge water from different sources. Furthermore, modeling results indicate that the groundwater age at 30m depth in Bejgoan Field Site is about 24-60 years old, which is consistent with the tritium age measurement at the same depth. The stable water isotope values in our study area shows a similar profile to the dissolved arsenic concentration, and their peak concentrations coincidence with the depth of irrigation well.
(cont.) Furthermore, comparison of calculated and measured isotopic values at the Bejgoan Field Site indicates that the calculated values are within the range of measured values, and thereby, confers that the observed isotopic profile results from the mixing of water from various recharge sources. More importantly, the lighter water at the depth of peak arsenic concentration can only be derived from lighter pond water recharge in November, whereas recharge from river and rainfall mainly occurs after March when those waters are actually heavier. Finally, observation of two distinct peaks in the dissolved arsenic concentration profile from a recently installed cluster beside a highly recharging pond provides a direct evidence supporting the "Pond Hypothesis". While the peak concentration at 30-40m depth corresponds to the characteristic regional hump observed in our study area, the second peak at a shallower depth (20m) has been explained as the local arsenic plume originating from the nearby pond bottom.
Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2010.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis. Page 290 blank.
Includes bibliographical references.
The shallow aquifers in Bangladesh, which provide drinking water for millions and irrigation water for innumerable rice fields, are severely contaminated with geogenic arsenic. Water mass balance calculations show that groundwater-irrigated rice fields and man-made ponds are the primary sources of recharge to the contaminated aquifers. We studied the hydrology and chemistry of these anthropogenic recharge sources to determine the impact they have on groundwater arsenic concentrations. Our hydrogeochemical investigation involved fieldwork, laboratory analyses, and modeling. The field research spanned three years and included the deployment of a sensor network to continually monitor soil moisture and water potential, tracer tests to visualize flow patterns, soil cores to determine soil properties, and soil and water samples to ascertain chemical characteristics. The large amount of generated data were synthesized with hydrologic, geochemical and mass-balance models. The study showed that physical and chemical differences between rice fields and ponds explain the spatial patterns of arsenic in the Bangladeshi aquifers. Recharge from rice fields is both temporally and spatially heterogeneous. It is focused through bunds (the raised boundaries around the perimeter of fields) and depends on irrigation intervals. Flow from ponds is constant and uniform through the pond sediments. These distinct hydrologic behaviors produce different water chemistries. Ponds contribute anoxic recharge elevated in labile organic carbon, while rice fields contribute semi-oxic recharge that lacks labile organic carbon.
(cont.) The labile organic carbon in the pond recharge stimulates microbial respiration that mobilizes sediment-bound arsenic, contributing dissolved arsenic to the aquifers. Conversely, rice-field recharge does not mobilize arsenic. In fact, rice fields act as an arsenic sink. Irrigation moves arsenic-rich groundwater from the aquifers and deposits it on the rice fields. Most of the deposited arsenic does not return to the aquifers; it is sorbed by the field's surface soil and bunds, and is swept away in the monsoon floods. The results demonstrate how land-use changes in Bangladesh have impacted groundwater arsenic concentrations.
by Rebecca B. Neumann.
Ph.D.

Volcanic rocks typically have only low to moderate arsenic concentrations, none-the-less, elevated levels of arsenic in ground waters have been associated with pyroclastic and volcaniclastic rocks and sediments in many parts of the world. The potential for arsenic leaching from these deposits is particularly problematic as they often comprise important water-bearing units in volcanic terrains. However, the role that chemical and mineralogical variations play in controlling the occurrence and mobility of arsenic from pyroclastic rocks is largely unexplored. This study uses chemical and X-ray diffraction data to characterize and classify 49 samples of ash-flow tuffs, and 11 samples of tuffaceous sediments. The samples exhibit a range of devitrification and chemical weathering. Total and partial digestion, and water extractions of samples are used to determine the total, environmentally available, and readily leachable fractions of arsenic present in all tuff samples. Leaching experiments were also performed with buffered solutions to determine the influence of elevated pH levels on arsenic mobility. The 49 tuff samples have a mean arsenic content of 7.5 mg kg-1, a geometric mean arsenic content of 4.8 mg kg-1, a median arsenic content of 5.2 mg kg-1, and a maximum arsenic concentration of 81 mg kg-1. The mean and median values are 2.8 - 4.4x the average crustal abundance of 1.7 mg kg-1 (Wedepohl, 1995), and consistent with previously reported values for volcanic glasses and felsic volcanic rocks (Onishi and Sandell, 1955; Wedepohl, 1995), although the maximum arsenic content is higher than previously reported (e.g., Casentini et al., 2010; Fiantis et al., 2010; Nobel et al., 2004). In addition, the arsenic concentrations of tuffs were found to be highly heterogenous, both between and within individual units, and in some cases, individual outcrops. Results of whole rock and leachate analyses indicate that there is no significant difference in the total arsenic content of tuffs as a result of devitrification or weathering, but both devitrified and weathered tuffs contain higher levels of environmentally available arsenic than unweathered glassy tuffs. Glassy tuffs did not produce any readily leachable arsenic, while individual devitrified and weathered tuffs both generated aqueous concentrations that exceeded regulatory limits after 18 hours. Leaching of weathered tuffs produced higher levels of arsenic at high (~9-11) pH than in tests conducted at circum-neutral pH. Devitrified and glassy tuffs showed no increase in leachable arsenic with increasing pH. The results of this study indicate that devitrification and weathering processes determine the host phases, degree of adsorption, and overall mobility of arsenic from ash-flow tuffs. Tuffs that have undergone different types of alteration are likely to have different host phases of arsenic, and different mechanisms that mobilize arsenic into the environment. Potential host phases and mobility mechanisms are discussed, and a conceptual model of arsenic behavior in ash-flow tuffs is proposed.

Arsenic contamination in drinking water is a severe problem worldwide. The best way to prevent hazardous diseases from chronic arsenic exposure is to remove the exposure. Efforts to remediate arsenic in drinking water have taken two tracks. One is to provide surface or shallow well water sources as an alternative to the arsenic contaminated deep wells. Another approach is to remove arsenic from the contaminated water. Different removal technologies like oxidation, chemical coagulation, precipitation, adsorption and others are available. There are problems and benefits associated with each of these approaches that can be related to cultural, socio-economic and engineering influences. The method proposed in this research is adsorption of arsenic to iron coated limestone. Different iron coated limestone samples were prepared. Standard solutions of 100ppb arsenic were prepared and batch and kinetic experiments were conducted. The final solution concentrations were analyzed by Graphite Furnace Atomic Adsorption Spectroscopy (GFAAs) and the results showed that iron coated limestone removed arsenic below 10ppb with 5 grams of material. Variations in iron coverage impacted efficiency of arsenic removal.

Tourism is acquiring the attention worldwide especially in the developing countries (Akpabio et al. 2006). In the case of coastal areas, tourism is more sensitive to environmental degradation compared to other economic activities because the environment is its primary resource. With the help of efficient planning and proper management of natural resources, tourism can significantly contribute to environmental conservation and to achieve environmental sustainability in coastal areas (Orhon et al. 2011). The main purposes of this study are to explore the tourism development trend in coastal areas of Cox’s Bazar, to analyse existing environmental conditions of Cox’s Bazar coastal area, to examine the importance of environmental sustainability at coastal region. More positively, the study shows environmental sustainability can be achieved through more eco-friendly planning of installations in tourism hubs like Cox’s Bazar. The main methods of conducting this study were desktop research; data collection through questionnaire survey and expert interview; data input in SPSS, processing and analysis; evaluation of policies, strategies and institutional framework. To formulate study goal and objectives, a comprehensive literature review has been conducted to understand about tourism, tourism development, sustainability, sustainable development by reviewing relevant reports, journals, and international cases which has helped to develop the conceptual framework of the study. After extensive literature review and formulation of goal and objectives, the conceptual framework of the study data collection instruments such as questionnaire has been prepared to collect data from the field. The study is largely based on the primary data collected through field visit, interviews to the experts on tourism and environment, and questionnaire survey at the study area, Cox’s Bazar. In this study, the statistical data on the study area has been collected from Bangladesh Bureau of Statistics (BBS). Apart from this, information has also been collected from various sources e.g. journals, projects, periodicals, and the daily newspapers, archives of both home and abroad. From the analysis, it found that Cox’s Bazar sea beach is a good place for tourism development, and it is also found that the level of tourism is improving gradually. Tourism in Cox’s Bazar mainly depends on natural beauty and environment of the coastal area. Tourism is producing long term negative effects on the coastal environment. If the environmental systems degrade tourism will not sustain any more. However, tourism can provide incentive for the conservation and restoration of the natural environment. Nearly half of the respondents stated that because of tourism, natural environment is in better condition in Cox’s Bazar and tourism provides incentive for the conservation and restoration of the natural environment. The analysis also identifies that policies and strategies play a big role to the conservation of natural environment and resources, and the implementation of principles of sustainable development. Government of Bangladesh (GoB) has been formulated some policies and strategies related to tourism development, sustainable development and coastal zone management, but most of the policies and strategies are not implemented properly because of institutional conflicts. In the light of the data analysis, discussion and findings, some recommendations are suggested here to help and guide future decisions regarding tourism development, conservation of the environment, sustainable development and sustainability at coastal areas in Bangladesh.
published_or_final_version
Urban Planning and Design
Master
Master of Science in Urban Planning

Graphite furnace and hydride generation atomic absorption, GFAA and HGAA, techniques have been developed and applied to the determination of arsenic concentrations in some marine invertebrates, mainly bivalves and gastropods, of British Columbia. Total arsenic concentrations in bivalves vary with species, ranging from 0.6-9.1 μg g⁻¹ (wet weight basis). Arsenic concentrations in the bivalve shells show a wider range of 0.1 to 26.3 μg g⁻¹ (dry weight basis). Gastropods show relatively higher arsenic concentrations in the soft tissues, 17.3-48.4 fig μg g⁻¹, and concentrations in the shells range from 1.4 to 16.3 fig μg g⁻¹. There is no correlation between arsenic levels in the soft-tissues and shells. There is also no correlation between arsenic levels in the organisms and the surrounding sediments and sediment pore waters. HPLC-GFAA techniques have been developed and used for the separation and quantitation of-arsenite, arsenate, methylarsonic acid, dimethylar-sinic acid, arsenobetaine, arsenocholine iodide and tetramethylarsonium iodide. This technique together with TLC, NMR, FAB and thermospray LCMS were employed for the detection of water-soluble arsenic compounds in 5 species of clams - Butter clam Saxidomus giganteus. Horse clam Schizothoerus nuttalli. Soft-shelled clam Mva arenaria. Native-littleneck clam Protothaca staminea and Manila clam Venerupis laponica. Varying amounts of arsenobetaine and tetramethylarsonium ion are found in all the clams. Butter clams show the pres ence of a third compound which appears to be trimethylarsine oxide. Small amounts of unknown arsenic containing compounds are present which are yet to be characterized . Arsenic speciation in 3 gastropods was also examined. The Northwest neptune Neptunea lvrata. the Thick-ribbed whelk Berinpius crebriscotata and Phoenician whelk Neptunea phoenicius all contain arsenobetaine and at least two unidentified arsenicals.
Science, Faculty of
Chemistry, Department of
Graduate

One hundred and eighty-six soil samples from Northwest Oregon were tested for arsenic content. The highest values measured were 13.9 ppm in the A horizon (site C4) and 20.4 ppm in the B horizon (Site P4). Arsenic was not detected in 28 A horizon samples and 23 B horizon samples. Data are grouped based on the age and rock type of underlying bedrock. Lithologic groups with six or more data points were compared statistically to ascertain if groups are distinct. Analysis of Variance (ANOVA) multiple comparison tests indicate that the arsenic content of the Marine Sediments and Sedimentary Rocks group samples is distinguishable from the Quaternary Basalts group in the A horizon and all other groups in the B horizon. Kruskal-Wallis multiple comparison tests indicate that the arsenic content of the Marine Sediments and Sedimentary Rocks group is distinguishable from the Quaternary Basalts, Quaternary/ Tertiary Sediments and Sedimentary Rocks and Volcanic Sediments groups in both the A and B soil horizons. The ANOVA and Kruskal-Wallis tests compared A and B horizon data by lithologic group. The ANOVA shows the Marine Sediments and Sedimentary Rocks group in the A horizon is distinct from the Quaternary Basalts in the A and B horizon. The Kruskal-Wallis test yielded the same result. Per the ANOVA, the Marine Sediments and Sedimentary Rocks in the B horizon are distinct from all other tested groups. The Kruskal-Wallis test shows the Marine Sediments and Sedimentary Rocks group in the B horizon as distinct from the Quaternary Basalts, Quaternary/ Tertiary Sediments, and Volcanic Sediments groups in the A and B horizon. A K-means cluster analysis was used to group all available data independent of underlying bedrock. Three, four, and five group analyses were conducted, and the results of these tests were compared to the data grouped by underlying rock type. No correlation between the groups resulting from the K-means cluster analysis and groups based on underlying lithology was found. This analysis supports the creation of a map distinguishing arsenic content in the soils above Marine Sediments and Sedimentary Rocks group units from arsenic content in all other tested lithologic groups. The mean and standard deviations of these groups (in ppm) are: A horizon: Marine Sediments (6.09 ±2.66); other groups (3.10 ±3.19); B horizon: Marine Sediments (10.26 ±4.65); other groups (3.13, ±2.52). This analysis indicates that geologic context must be taken into account when determining background levels of naturally occurring arsenic in soils.

Exposure to arsenic in drinking water can cause several types of cancer and numerous cardiovascular and respiratory diseases. A country that suffers from widespread contamination of arsenic in drinking water is Bangladesh, where the contamination has been classified as the largest mass poisoning of a population in history. Around 90 percent of the existing tubewells used for drinking water in Bangladesh were installed by the private sector and local drillers, which makes their knowledge on drinking water contamination crucial in order to make them contributory for scaling up access to safe drinking water. The aim of the thesis was to develop an interactive map model to enhance the access to information for the local governments, communities, and private sector in three upazilas (sub- districts) of Bangladesh: Assasuni, Daudkandi, and Gowainghat, regarding how they can access safe drinking water in their local areas. The interactive map model for this thesis was developed in ArcGIS with supporting information from local drillers’ survey and Arsenic Safe Union project implementation data. The resulting maps contain information such as wells located in the upazilas, drillers’ working areas, years of working experience, contact information, certification and driller hubs (hardware shops). The map model is expected to be operationalised by creating a digital water platform through a mobile application, in a stand-alone website, or to be integrated in a government information centre to enable access for the community, local technocrats, the private sector and other concerned stakeholders. Moreover, the map can easily be scaled-up in the future to include additional areas with similar hydrogeology and arsenic or trace elements contamination problems, in other regions of South Asia, Africa and Latin America.
Exponering för arsenik i dricksvatten kan orsaka flera olika typer av cancer samt ett flertal hjärt- och luftvägssjukdomar. Ett land som är utsatt för utbredd arsenikförorening i dricksvatten är Bangladesh, där föroreningen har klassificerats som den största massförgiftningen av en befolkning i historien. Ungefär 90 procent av alla existerande dricksvattensrörbrunnar i Bangladesh installerades av den privata sektorn och av lokala brunnsborrare, vilket gör deras kunskap om dricksvattenföroreningar avgörande för att de ska kunna bidra till att öka tillgången till säkert dricksvatten. Syftet med denna uppsats var att utveckla en interaktiv kartmodell för att öka tillgången till information för lokala myndigheter och samhällen, samt för den privata sektorn i tre upazilor (kommuner) i Bangladesh: Assasuni, Daudkandi och Gowainghat, angående hur de kan få tillgång till säkert dricksvatten i deras område. Den interaktiva kartmodellen utvecklades i ArcGIS och innehåller information från en enkät ifylld av lokala brunnsborrare samt data från projektet Arsenic Safe Union. De resulterande kartorna innehåller information om brunnar belägna i upazilorna, information om lokala brunnsborrares arbetsområden samt deras arbetserfarenhet, kontaktinformation, certifiering och brunnsborrarnav (järnhandlare). Kartmodellen förväntas göras tillgänglig för samhället, lokala myndigheter, den privata sektorn och andra berörda aktörer, genom en digital vattenplattform i en mobilapplikation, på en fristående webbplats eller genom att integreras i ett statligt informationscenter. I framtiden kan kartan enkelt skalas upp för att inkludera ytterligare områden med liknande hydrogeologi och föroreningsproblem, till följd av arsenik eller andra spårelement, för regioner i Sydasien, Afrika och Latinamerika.

The primary objective of this thesis is to differentiate between the risk factors for pre-and post-monsoon cholera epidemics in rural Bangladesh by analyzing the complex interaction between select environmental, cultural/behavioral, and socioeconomic variables over space and time. In rural Bangladesh, cholera epidemics correspond with the annual monsoon: the first, and smallest, occurs between March and June, while the larger cholera peak occurs between September and December. The differences between the spatial and temporal patterns of seasonal cholera are analyzed, and the risk factors are calculated for pre-and post-monsoon cholera epidemics. The theoretical approach that underlies this medical geographical study is disease ecology, which espouses that risk of disease is caused by an interaction between people and their environment. This thesis is structured around a holistic understanding that human-environment interactions are inseparable. In Bangladesh, the monsoon season typically starts between May and June. The 1992 and 1993 cholera peaks occurred just before the monsoon in April and March respectively, while the 1994 cholera peak occurred between April and June. In 1992 and 1993 cholera incidence increased in the post-monsoon period, and peaked in October. The 1994 post-monsoon cholera peak occurred in November. There is a regular temporal pattern to cholera, as the peaks followed a seasonal pattern with the smaller epidemic occurring in the pre-monsoon period and the larger epidemic occurring in the post-monsoon period. This study shows that there are different risks associated with pre-monsoon cholera epidemics and post-monsoon cholera epidemics. The two main risk factors associated with cholera incidence pre-monsoon were bari population (i.e., crowding) and a house located within the flood controlled area. These two variables were even more strongly associated with post-monsoon cholera incidence to a greater degree, along with a number of other variables including water use, sanitation practices, and socioeconomic status.

Several biologically important arsenic compounds including methylarsonate, trimethylarsine oxide, tetramethylarsonium ion, arsenobetaine and arsenocholine were prepared, in good yields, from sodium arsenite, or dimethylarsinic acid. These organoarsenic compounds together with arsenite, arsenate and dimethylarsinic acid were used as standards for the development of analytical methods for determining the levels of individual arsenic compounds (arsenic speciation) present in natural matrices.
Arsenobetaine, arsenocholine and tetramethylarsonium ion were separated by high performance liquid chromatography (HPLC) with on-line detection by thermochemical hydride generation (THG)-AAS. The analytes were eluted from the cyanopropyl bonded phase HPLC column with a 1% acetic acid methanolic mobile phase which also contained diethyl ether triethylamine, and trimethylsulfonium iodide or picrylsulfonic acid. A surface response methodology and a univariate optimization procedure were used to determine the optimum concentration of solvent modifiers in the methanolic mobile phase. Limits of detection in the range 4-5 ng (as As) were obtained for the arsonium analytes under optimum chromatographic conditions.
A simple phenol extraction procedure was developed to isolate arsonium analytes from edible marine tissues (lobster tail muscle, peeled and deveined shrimp, and cod fillet), cod liver oil and human urine. The crude extracts were separated on the cyanopropyl column using a methanolic mobile phase and detected on-line by THG-AAS. Recoveries from tissues or from urine which had been spiked at 0.1-3.4 $ mu$g of As cation/g of fresh weight were 80% or greater for each of five sample types.
An improved HPLC-AAS interface which was compatible with either aqueous or organic mobile phases was also developed. The interface provided approximately equivalent responses to different arsenic oxidation states which resulted in low to subnanogram chromatographic limits of detection for arsenic oxyanions and arsonium cations in an aqueous or methanolic mobile phase. Nascent As anions and As cations were conveniently coextracted from aqueous solution or from fish muscle by phenol extraction and quantified in the same chromatographic run. This method has been applied to a standard reference sample of dogfish muscle (DORM-1), a marine reference sediment sample (PACS-1) and to sediment porewaters (SAG-15) from the Saguenay Fjord.

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.

This thesis is composed of three independent essays. In the first chapter, I analyze the effect of a biofuel-favorable policy in the U.S. on fetal health. I show that the policy led to an expansion in the production of corn, a pesticide-intensive crop, and to increased risk of fetal conditions previously associated with exposure to corn pesticides. In the second chapter, I examine the role of agricultural productivity as a mechanism linking rainfall shocks to civil wars in African countries. I show that rainfall over agricultural land and during the growing season has a hump-shaped relationship with agricultural output, which is mirrored by a U-shaped relationship with civil war risk. In the third chapter, I examine the effect of various selling schemes for testing tubewell water for arsenic on test uptake and, conditional on adverse news, on health-protective behavior. I find that uptake is increased by fees that depend on test results, and that social networks and public information can promote health-protective behavior.
Esta tesis consta de tres ensayos independientes. En el primer capítulo, analizo el efecto de una ley estadounidense que favorece la producción de biocombustibles sobre la salud fetal. Demuestro que la ley aumentó la producción de maíz, un cultivo con altos requerimientos de pesticidas, y el riesgo de enfermedades fetales asociadas con la exposición a pesticidas. En el segundo capítulo, estudio cómo la productividad agrícola puede mediar la relación entre shocks de lluvia y guerras en países africanos. Midiendo el nivel de lluvia sobre el territorio agrícola y durante la fase de crecimiento, demuestro que éste tiene una relación en forma de U-invertida con la producción agrícola, y una relación en forma de U con la incidencia de guerras civiles. En el tercer capítulo, estudio el efecto de diversas modalidades de venta de pruebas de arsénico para agua de pozo sobre la demanda por las mismas y, para familias que reciben noticias adversas, sobre su comportamiento para evitar el arsénico. Encuentro que la demanda aumenta cuando el precio a pagar depende de los resultados de la prueba, y que las redes sociales e información pública pueden promover medidas para evitar el agua contaminada.

Trace metals (e.g. Fe, Mn, Zn, Cu, Cd, Ni) are important micronutrients that have historically been regarded as toxic pollutants rather than essential components of riverine and estuarine environments. The toxicity and behavior of trace metals, in response to physical and biogeochemical processes, are determined by their individual physico-chemical properties. In this dissertation, the vertical transformation of trace metals across oxic-anoxic interfaces was investigated at two sites, a Fe-rich freshwater river with minimal sulfide and an estuary with elevated Mn and H2S concentrations. Sediment profiles obtained from the Chattahoochee River showed that dissolved arsenic, present as As(V) only, is scavenged by Fe-oxides and accumulates directly below the sediment-water interface. Depth profiles also indicate that As(V) fluxes into the overlying water during baseflow conditions as well as after storm events. The significant correlation between Fe(II) and As(V) suggest that As(V) is released from Fe-oxides during their microbial reduction. By implementing a series of sediment incubations under increasing As(V) loads, it was determined that adsorption onto Fe-oxides and microbially mediated reductive dissolution of these mineral phases drive arsenic cycling in this sediment. These incubations also reveal for the first time that arsenic, even in low concentrations, n turn, arsenic loading impacts iron cycling by stimulating anaerobic respiration of Fe-oxides and promoting recrystallization of authigenic Fe-oxides, up to a toxicity threshold up to a few micromolar in concentrations. A combination of in situ measurements with discrete water sampling was utilized to determine the effects of tidal cycling on the distribution of trace metals under changing redox conditions during two consecutive tidal cycles at Station 858 in the Chesapeake Bay. Estuarine circulation patterns driven by tidal oscillations, a defined pycnocline, and the shallow sill (~20 m) of the Chesapeake Bay promoted bottom water anoxia during the summer months that allowed dissolved sulfide and reduced manganese to accumulate below the oxycline. The distribution of barium (conservative freshwater tracer) and uranium (conservative seawater tracer) across the pycnocline over the two tidal cycles indicated that the source of dissolved species was surficial sediments. During ebb and flood tides, the shear stress from the bottom waters flowing over the sediment seems to episodically promote the advection of porewaters enriched in dissolved sulfide, manganese, uranium, barium, lead, chromium, and copper. The selective enrichment of these trace metals appears to be controlled by their reactivity with sulfide. In contrast, cobalt and nickel are retained in sediments by adsorbed or incorporated in FeS and FeS2, while arsenic co-precipitates with sulfide or iron sulfide minerals. Overall, this study demonstrates that natural aquatic systems are complex environments where the interplay between biological, chemical, and physical processes affects the distribution of trace metals over short time scales. While a great wealth of knowledge can be obtained by laboratory experiments with synthetic solutions or pure cultures of organisms, a combination of in situ measurements and incubations with real samples in necessary to characterize the processes regulating the cycling of trace metals in aquatic systems.

High concentrations of arsenic are found near gold-mine tailings. The most common form of arsenic found in soil is arsenate, which is a known toxicant. We used the standardised earthworm reproduction test for the species Eisenia andrei (E. andrei) to study the toxicity and bioavailability of arsenic-contaminated soil. Arsenic is toxic to earthworms as indicated by the decrease in survival and reproduction. Arsenic-spiked artificial soil was more toxic than arsenic-spiked field soil based on total arsenic concentration in soil. Moreover, soil from near mine tailings showed a reduced toxic effect despite its high soil arsenic concentration as compared to spiked field soil. Measurements of arsenic tissue concentrations in the earthworm indicated that uptake of arsenic into earthworm tissue was higher in spiked artificial soil as compared to spiked field soil and that the maximal body burden was 396 mug As/g dry tissue weight. However, when considering tissue arsenic concentration, spiked field soil is more toxic than spiked artificial soil. Therefore the tissue rather than soil content may better reflect the magnitude of arsenic toxicity to E. andrei.

Rocks of the South Island of New Zealand are locally enriched in metalloids, namely arsenic (As), antimony (Sb) and boron (B). Elevated levels of As and Sb can be found in sulphide minerals mostly in association with mesothermal gold deposits, whereas B enrichment occurs in marine influenced coal deposits. The mobility of these metalloids is important because they can be toxic at relatively low levels (e.g. for humans >0.01 mg/L of As). Their mobilisation occurs naturally from background weathering of the bedrock. However, mining and processing of coal and gold deposits, New Zealand's most economically important commodities, can significantly increase metalloid mobility. In particular, historic mines and associated industrial sites are known to generate elevated metalloid levels because of the lack of site remediation upon closure. This work defines and quantifies geological, mining, post-mining and regional processes with respect to metalloid, especially As, mobility. At the studied historic gold mines, the Blackwater and Bullendale mines, Sb levels in mineralised rocks were generally negligible (<14 ppm) compared to As (up to 10,000 ppm). Thus, Sb concentrations in solids and in water were too low to yield any meaningful information on Sb mobility. In contrast, dissolved As concentrations downstream from mine sites were found to be very high (up to 59 mg/L) (background = 10⁻� mg/L). In addition, very high As concentrations were found in residues (up to 40 wt%) and site substrate (up to 30 wt%) at the Blackwater processing sites (background < 0.05 wt%). Here, roasting of the gold ore converted the orginal As mineral, arsenopyrite, into the mineral arsenolite (As[III] trioxide polymorph) and volatilised the sulphur. The resultant sulphur-defficient chemical system is driven by arsenolite dissolution and differs significantly from mine sites where arsenopyrite is the main As source. Arsenolite is significantly more soluble than arsenopyrite. In the surficial environment, arsenolite dissolution is limited by kinetics only, which are slow enough to preserve exposed arsenolite over decades in a temperate, wet climate. This process results in surface waters with up to ca. 50 mg/L dissolved As. In reducing conditions, dissolved As concentrations are also controlled by the solubility of arsenolite producing As concentrations up to 330 mg/L. Field based cathodic stripping voltammetry showed that the As[III]/As[V] redox couple, in particular the oxidation of As[III], has a major control on system pH and Eh. Site acidification is mainly caused by the oxidation of As[III], resulting in a close link between As[V] concentrations and pH. Similarly, a strong correlation between calculated (Nernstian) and measured (electrode) Eh was found in the surface environment, suggesting that the overall Eh of the system is, indeed, defined by the As[III]/As[V] redox couple. Once the metalloid is mobilised from its original source, its mobility is controlled by at least one of the following attenuation processes: (a) precipitation of secondary metalloid minerals, (b) co-precipitation with - or adsorption to - iron oxyhydroxide (HFO), or (c) dilution with background waters. The precipitation of secondary minerals is most favoured in the case of As due to the relatively low solubility of iron arsenates, especially at low pH (~0.1 mg/L). Observations suggest that scorodite can be the precursor phase to more stable iron arsenates, such as kankite, zykaite, bukovskyite or pharmacosiderite and their stability is mainly controlled by pH, sulphur concentrations and moisture prevalence. Empirical evidence indicates that the sulphur-containing minerals zykaite and bukovskyite have a similar pH dependence to scorodite with solubilities slightly lower than scorodite and kankite. If dissolved As concentrations decline, iron arsenates potentially become unstable. Their dissolution maintains a pH between 2.5 and 3.5. This acidification process is pivotal with respect to As mobility, especially in the absence of other acidification processes, because iron arsenates are several orders of magnitude more soluble in circum-neutral pH regimes (~100 mg/L). From this, it becomes apparent that external pH modifications, for example as part of a remediation scheme, can significantly increase iron arsenate solubility and resultant As mobility. In contrast to As, the precipitation of secondary Sb and B minerals is limited by their high solubilities, which are several orders of magnitude higher than for iron arsenates. Thus, secondary Sb and B minerals are restricted to evaporative waters, from which they can easily re-mobilised during rain events. Metalloid adsorption to HFO is mainly controlled or limited by the extent of HFO formation, which in turn is governed by the availability of Fe and prevailing Eh-pH conditions. Thus, mineralisation styles and associated geochemical gradients, in particular pyrite abundance, can control the amount of HFO and consequent metalloid attenuation, and these can vary even within the same goldfleld. Furthermore, it was found that there is a mineralogical gradation between ferrihydrite with varying amounts of adsorbed As, amorphous iron arsenates and crystalline iron arsenates, suggesting that the maturity of mine waste is an important factor in As mineralogy. Once dissolved metalloids enter the hydrosphere, dilution is the main control on metalloid attenuation, which is especially pronounced at the inflow of tributaries. Dilution is, therefore, closely related to the size and frequency of these tributaries, which in turn are controlled by the regional topography and climate. Dilution is a considerably less effective attenuation mechanism and anomalous metalloid concentrations from mining related sites can persist for over 10 km downstream. The complex and often inter-dependent controls on metalloid mobility mean that management decisions should carefully consider the specific site geochemistry to minimize economic, health and environmental risks that can not be afforded. On a regional scale, background metalloid flux determines the downstream impact of an anomalous metalloid source upstream. For example, the Bullendale mine is located in a mountainous region, where rapidly eroding slopes expose fresh rock and limit the extent of soil cover and chemical weathering. Consequently, the background As flux is relatively low and As point sources, such as the Bullendale mine, present a significant contribution to the downstream As flux. In contrast, the bedrock at the Blackwater mine has undergone deep chemical weathering, resulting in an increased background mobilisation of As. Thus, the Prohibition mill site discharge, for example, contributes only about 10% to the downstream As flux. This information is relevant to site management decisions because the amount of natural background metalloid mobilisation determines whether site remediation will influence downstream metalloid chemistry on a regional scale.

This thesis sets out to develop a beginning of a philosophy of water by considering philosophical implications of ecological crises currently happening along the waters of the Ganges River. In my first chapter, I give a historical account of a philosophy of water. In my second chapter, I describe various natural and cultural representations of the Ganges, accounting for physical features of the river, Hindu myths and rituals involving the river, and ecological crises characterized by the pollution and damming of the river. In my third and final chapter, I look into the philosophical implications of these crises in terms of the works of the contemporary philosopher Bruno Latour.

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.

Inorganic arsenic exposure is a well-known toxicant of which we are still discovering harmful effects. People are exposed to inorganic arsenic in the environment through either drinking arsenic-contaminated groundwater or consuming arsenic-contaminated food. Regarding global public health, drinking water is still the most important source of inorganic arsenic exposure and is the main focus of this work. The overall goal of this dissertation is to answer some pointing epidemiological questions about exposure to inorganic arsenic: How much do we know about inorganic arsenic and non-malignant lung disease in the general population? To what extent are adolescents with lifetime arsenic exposure susceptible to the respiratory consequences seen in adults? And what actions can be taken to effectively reduce exposure from arsenic-contaminated drinking water? First, we conducted a systematic review of 29 peer-reviewed articles from various populations around the world. The review focused on the different ways in which arsenic is associated with respiratory health to help inform policy makers and public health researchers on the existing evidence. In short, associations between arsenic and respiratory health were noted throughout the lifespan: in infancy, there was growing evidence that in utero arsenic exposure was associated with increased frequency and severity of respiratory tract infections; in childhood, evidence of respiratory symptoms also began to appear; and in adulthood, there was consistent evidence that arsenic exposure was associated with deficits in lung function and increased reports of coughing and breathing problems. The review also uncovered some research gaps, including few studies with strong exposure history from early life and few studies examining respiratory effects during adolescence. Next, we used a life course epidemiological approach to create a more precise understanding of arsenic exposure and respiratory health during the teenage years. This study examined the relationship between lifetime arsenic exposure and lung function in 14-17 year olds, thus studying the period of maximal lung function before natural decline. Overall, higher arsenic exposure was associated with lower lung function levels; however, these associations were only observed in males. This study used a sensitive marker of lung function to investigate early signs of small airway disease. Incorporating this common marker of small airway disease and airflow limitation in future studies on arsenic and respiratory health may help clarify how inorganic arsenic contributes to the development of chronic respiratory disease. Lastly, we evaluated the effectiveness of arsenic removal filters at the household-level in rural Bangladesh. Identifying sustainable ways of reducing exposure to arsenic from naturally contaminated groundwater has been a major environmental health challenge. Although lab-approved arsenic removal water filters exist, there was limited evidence of their prolonged efficacy in the field. To our knowledge, this was the largest and longest deployment of filters accompanied by monitoring of urinary arsenic. Our results demonstrated that filters can temporarily reduce arsenic exposure for weeks to a few months, but should not be considered as a long-term arsenic mitigation option. This failed attempt to reduce exposure confirmed that alternative mitigation strategies need to be employed in Bangladesh, particularly among more vulnerable populations, including pregnant women and young children. This dissertation has important policy implications for future arsenic research and mitigation efforts and should be effectively communicated to policy makers, public health officials, and the general population. Given the pervasive nature of arsenic exposure and the growing evidence of health consequences at different stages throughout the life course, the continued integration of information on inorganic arsenic and research collaborations across disciplines is critical for the prevention and mitigation of arsenic-induced health consequences.

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.

Millions of villagers in Bangladesh drink water which exceeds the Bangladesh arsenic (As) standard of 50 micrograms per liter. Exposure to elevated levels of inorganic As (As) is associated with cancers of the skin, bladder, and lung, developmental effects, cardiovascular disease, skin lesions, and decreased children's intellectual functioning. Arsenic mitigation typically involves an outsider coming into a village to test the well water for As. After the results of the As test are provided this person typically leaves the village without providing the resources to address health concerns or give advice on mitigation options. In this dissertation, in an effort to provide ongoing resources on the health implications of As and to reduce As exposure, we sought to evaluate community level intervention strategies that could be used for successful As mitigation in Bangladesh. In Singair, Bangladesh, we conducted a household drinking water survey of 6649 households. The results of our survey indicated that 80% of wells were untested for As. Furthermore, we demonstrated that testing all of these untested wells would increase the number of households that lived with fifty meters of an As safe drinking water source by nearly 2.5 fold. In a cluster based randomized control trial (RCT) of 1000 households, we evaluated the effectiveness of having community members, compared to outside representatives, disseminate As education and conduct water As (WAs) testing. In 10 villages, a community member disseminated As education and provided WAs testing. In a second set of 10 villages an outside representative performed these tasks. Overall, fifty three percent of respondents with unsafe wells at baseline switched after receiving the As education and WAs testing intervention. There was no significant association observed between the type of As tester and well switching (Odds ratio (OR) =0.77; 95% confidence interval (CI) (0.37-1.61)). At follow-up, the average UAs concentrations for those with unsafe wells at baseline who switched to safe wells significantly decreased. In both intervention groups a significant increase in knowledge of As was observed at follow-up compared to baseline. The unavailability of As-safe drinking water sources in some villages was the most substantial barrier to well switching identified. The Hach EZ As field test kit measurements conducted by the As testers were highly correlated with laboratory results. This finding indicates that the As testers were able to accurately measure the WAs concentration of wells. Furthermore in our pilot study, the performance of the Econo-Quick (EC) kit, a new field WAs testing kit, was comparable to that of the commonly used EZ kit and the Wagtech Arsenator kit. The EC kit has the advantage of a substantially shorter reaction time of only 12 minutes in comparison to the 40 minutes required by these other kits. Through this dissertation, we have demonstrated that As education and WAs testing programs can be used as an effective method to reduce As exposure and increase As awareness in many As affected areas of Bangladesh. Furthermore, our findings indicated that many households are using tubewells that are untested for As therefore demonstrating the urgent need for access to water As testing services.

This dissertation examines the potential of information-provision in motivating behavior that reduces human exposure to arsenic in drinking-water in Bangladesh. In chapter 2, the longer-term effects of the countrywide arsenic-testing and information-program are examined by tracking tube-well switching behavior of households over a five-year period. Chapter 3 focuses on the effects of arsenic information communication formats on tube-well switching behavior, by employing a randomized field experiment. In chapter 4, an instrumental variables approach is used to understand whether a household's decision to switch sources is affected by its proximate neighbors' decisions to switch sources. To answer these questions, primary data was collected by the researchers through field-work in Bangladesh. The results suggest that arsenic-testing and information-provision programs produce persistent behavioral changes that reduce exposure to arsenic, with their impact increasing over time. Comparing the impacts of risk-communication formats, we find that quantitative formats do not significantly increase source-switching behavior, in comparison to that generated by qualitative formats. Lastly, despite econometric identification issues, our data suggest that households gather information about source-switching by observing the actions of their neighbors. In sum, the results presented in this dissertation suggest that the provision of information to rural households can motivate health-improving behavior that reduces households' exposure to arsenic in Bangladesh. This dissertation contributes to the use of information disclosure as a policy instrument to reduce exposure to environmental contaminants.

Dissertation

The worldwide natural occurrence of high levels of arsenic (As) in groundwater and its deleterious effects on human health have inspired a great amount of related research in public health and geosciences internationally. With >100 million people in South and Southeast Asia exposed to >10 µg/L As in shallow groundwater that they use for drinking, the installation of deeper, low-As wells has emerged as a major strategy for lowering the exposure. As the magnitude of deep pumping continues to increase, this work focuses on the geochemical and hydrologic questions surrounding the vulnerability and sustainability of low-As aquifers in Bangladesh, the country most affected by As crisis. In an effort to better understand the residence time of groundwater in low-As aquifers at depth, radiocarbon (14C) and 13C in dissolved inorganic carbon, tritium (3H), stable isotopes of hydrogen (2H) and oxygen (18O), and noble gas concentrations were measured across a ~25 km2 area of Araihazar, ~30 km east of Dhaka. Groundwater from >120 m depth is shown to be ~10,000 years old and its isotopic signatures indicate that recharge occurred at the time of changing climate from the late Pleistocene to early Holocene, with little recharge occurring since. In contrast, the intermediate depth low-As aquifers (<120 m) have a heterogeneous distribution of groundwater chemistry and ages, and contain groundwater recharged <60 years ago in certain locations. In one such area surrounding a small village, the effects that subsurface clay layer distribution has on recharge patterns and redox status of the intermediate aquifer was investigated. The relevant hydrogeologic and geochemical processes that led to documented failures of a community well at the site were assessed using a combination of solid and water phase geochemistry with tritium-helium (3H/3He) dating, hydraulic head monitoring, and pumping tests. Organic matter seeping from a compressible clay layer, which is subject to a pumping-induced, downward hydraulic gradient, reduces iron oxides and helps release As in the grey, upper part of the intermediate aquifer. No recent recharge was detected by 3H measurements in the upper, grey sand layer, however a layer of orange sand beneath it contains groundwater that was recharged 10-60 years ago. This groundwater laterally bypasses the confining clay layer to recharge the middle of the aquifer and contains dissolved As levels of <10 µg/L. In this particular case, the pore water that leaches from clay layers contributes to As contamination, whereas the lateral recharge with shallow groundwater coincides with the low-As depth. Thus, clay layers may not always protect the low-As aquifers from As contamination, even if they can block direct vertical recharge with shallow groundwater enriched in As and organics. Finally, the adsorption of As to aquifer sediments, as a natural mechanism of the low-As aquifer defense against contamination, was assessed in the field via a column study. The column experiments were conducted by pumping shallow, high-As groundwater through freshly collected sediment cores to quantify the retardation of As transport through the aquifer. This study demonstrated an elegant method of assessing contaminant transport under nearly in situ conditions that resulted in sorption estimates similar to those made by field studies using more challenging methods or located at hard-to-find sites with convenient flow patterns. My work, therefore, contributed to a better understanding of low-As aquifers in Bangladesh from the perspectives of both the groundwater flow and water-sediment interactions on various scales, and it integrated methods that can be employed elsewhere to characterize aquifers and study contaminant transport.

Background: Environmental exposure to inorganic arsenic (InAs) is a considerable worldwide problem, and over 57 million people in Bangladesh have been chronically exposed to arsenic-contaminated drinking water. Ingested inorganic arsenic (InAs) undergoes hepatic methylation generating monomethyl- (MMAs) and dimethyl- (DMAs) arsenic species in a process that facilitates urinary As (uAs) elimination. Of these three metabolites (InAs, MMA and DMA), MMA the most toxic, InAs is the second most toxic, and DMA is the least toxic. Consequently, increased MMAs is associated with increased risk of As-related adverse health outcomes. One-carbon metabolism (OCM), the biochemical pathway that provides methyl groups for As methylation, is influenced by folate and B12. A growing body of research, including cell-culture, animal-model, and epidemiological studies, have demonstrated the role of OCM-related micronutrients in As methylation. While folate supplementation is known to increase As methylation and lowers blood As (bAs) in adults, little data is available for adolescents. OCM also supports nucleotide and amino acid synthesis, particularly during periods of rapid growth, such as adolescence. In Bangladesh, deficiencies in folate and vitamin B12 are widespread. These micronutrients are essential for OCM and As methylation, and they are also critical for neural development, since they are necessary for the synthesis of neurotransmitters and myelin, and critical for generation of S-adenosyl-methionine (SAM) via OCM. Deficiencies in folate and B12 have been shown to negatively influence cognitive function in adults and children, but this has not been adequately characterized in adolescents. Individuals living in Bangladesh, facing As exposure and nutritional deficiency, also experience environmental exposure to elevated levels of cadmium (Cd), manganese (Mn), and lead (Pb). These metals have been linked to adverse neurocognitive outcomes in adults and children, though their effects on adolescents are not yet fully characterized. Additionally, previous studies have linked selenium (Se) levels to protective effects against toxicity of these other metals, as Se is an essential nutrient. Metal mixtures are also understudied in adolescents, and more research is needed. Objectives: Firstly, the research presented in this dissertation will examine the previously published evidence that nutritional status and nutritional interventions can influence the metabolism and toxicity of As, with a primary focus on folate. Secondly, the associations between OCM-related micronutrients and As methylation in Bangladeshi adolescents chronically exposed to As-contaminated drinking water will be studied. Thirdly, this dissertation will investigate the associations between folate and B12 nutritional status, homocysteine, and cognitive function as measured by two different test instruments in Bangladeshi adolescents. Finally, the associations between mixed metals exposure and cognitive function in Bangladeshi adolescents will be examined. Methods: The Metals, Arsenic, & Nutrition in Adolescents study (MANAs) is a cross-sectional study of 738 Bangladeshi adolescents aged 14-16 years, whose parents were enrolled in our group’s previous Health Effects of Arsenic Longitudinal Study (HEALS). Venous blood samples were collected from adolescent participants for measurement of plasma folate, red blood cell (RBC) folate, plasma B12, plasma homocysteine (Hcys), blood As (bAs), blood cadmium (bCd), blood manganese (bMn), blood lead (bPb), and blood selenium (bSe). Urine samples were collected for measurement of urinary arsenic and urinary arsenic metabolites (InAs, MMA, and DMA) expressed as a percentage of total urinary As: %InAs, %MMAs, %DMAs. Additionally, participants completed a modified version of the Wechsler Intelligence Scale for Children-Fourth Edition (WISC-IV) and an abbreviated version of the Cambridge Neuropsychological Test Automated Battery (CANTAB). Associations between predictors and outcomes were assessed using linear regression analyses. Associations for the mixture of metals were also examined via Bayesian Kernel Machine Regression (BKMR), which assessed the effects of the metals mixture in addition to examining the effects each individual metal component. Results: In the linear regression analyses examining associations between nutritional status and arsenic methylation profiles controlling for water As and BMI, in girls we observed that RBC folate was inversely associated with bAs, plasma B12 was inversely associated with uAs, and, somewhat unexpectedly, plasma Hcys was inversely associated with %MMA. Among boys, we saw that plasma folate was inversely associated with %InAs and positively associated with %DMA, RBC folate was inversely associated with %InAs and positively associated with %MMA, while Hcys was positively associated with %InAs. In linear regression analyses examining the associations between nutritional status and cognitive function controlling for covariates, we found no significant associations between nutritional status and cognitive function as measured by WISC. For cognitive function as measured by CANTAB, we observed positive associations between plasma folate and spatial recognition memory, and between plasma B12 and spatial working memory. In our investigation of the associations between metal exposures and cognitive outcomes, linear regression analysis revealed negative associations between exposure to As and Mn and spatial working memory. Negative associations were also seen between bCd and Spatial Recognition Memory, and between bPb and Delayed Match to Sample. Finally, a positive association was seen between bSe and Spatial Span Length. Our BKMR results showed no overall effect of the mixture but further characterized the associations for individual metals within the mixture. BKMR analyses indicate that bPb has a negative association to Delayed Match to Sample, and that there are positive associations between bSe and Planning, Reaction Time, and Spatial Span. BKMR also showed higher concentrations of bCd to be negatively associated with Spatial Recognition Memory. Posterior inclusion probability consistently rated Se, which has a protective effect, as the most influential component of the mixture. Conclusions: These findings suggest that associations between OCM nutritional status, blood arsenic, and distribution of urinary As metabolites in adolescents are similar to previously reported observations in adults and in children. The inverse association between Hcys and %MMA in girls is unexpected since Hcys is known to be an indicator of impaired OCM and low folate/B12 in adults. These findings also suggest that associations between nutritional status and cognitive function in adolescents are consistent with previously reported associations in adults and children. The observation of positive associations between folate and spatial recognition memory and between B12 and spatial working memory are consistent with findings in animal models, children, and adults, all of which link deficiencies in these two micronutrients to memory deficits. The findings of the metals investigation are also consistent with previously reported observations in adults and children, and these results also suggest agreement between linear regression and BKMR analysis of the mixed metal exposure, with the BKMR further demonstrating associations seen in the linear regression analysis. Generally, Se had a protective effect for cognitive outcomes, whereas Mn and As were linked to poorer working memory, and Cd and Pb were linked to poorer visual recognition and memory. BKMR reinforced and further characterized results of the linear regression analyses. Overall, these results indicate that the associations between OCM-related micronutrients, arsenic methylation, metal exposure, and cognitive function in adolescents are generally similar to prior findings in adults and children. However, additional studies are needed to evaluate the impact of OCM and As methylation on As-related adverse health outcomes (such as cancer and cardiovascular disease) in people exposed to As during adolescence. These results also suggest that further investigation into the associations between nutritional status and measures of cognitive function in adolescents is merited, and that further exploration of homocysteine’s role in adolescent physiology is needed. Most importantly, these findings suggest that both nutritional interventions involving B12 and folate supplementation and metal exposure mitigation efforts may have a positive impact on overall health and well-being for individuals facing these environmental exposures. In the long term, interventions to reduce exposure to metals and nutritional deficiency, and interventions to attenuate the effects of these exposures have the potential to influence lifelong cognitive function, possibly influencing professional achievement and economic outcomes in regions having a high prevalence of nutritional deficiencies, arsenic exposure, and environmental exposure to metals mixtures.

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.

Arsenic is a naturally occurring toxic metal and its presence in food composites could be a potential risk to the health of both humans and animals. Arseniccontaminated groundwater is often used for food and animal consumption, irrigation of soils, which could potentially lead to arsenic entering the human food chain. Its side effects include multiple organ damage, cancers, heart disease, diabetes mellitus, hypertension, lung disease and peripheral vascular disease. Research investigations, epidemiologic surveys and total diet studies (market baskets) provide datasets, information and knowledge on arsenic content in foods. The determination of the concentration of arsenic in rice varieties is an active area of research. With the increasing capability to measure the concentration of arsenic in foods, there are volumes of varied and continuously generated datasets on arsenic in food groups. Visual analytics, which integrates techniques from information visualization and computational data analysis via interactive visual interfaces, presents an approach to enable data on arsenic concentrations to be visually represented. The goal of this doctoral research in Environmental Science is to address the need to provide visual analytical decision support tools on arsenic content in various foods with special emphasis on rice. The hypothesis of this doctoral thesis research is that software enabled visual representation and user interaction facilitated by visual interfaces will help discover hidden relationships between arsenic content and food categories. The specific objectives investigated were: (1) Provide insightful visual analytic views of compiled data on arsenic in food categories; (2) Categorize table ready foods by arsenic content; (3) Compare arsenic content in rice product categories and (4) Identify informative sentences on arsenic concentrations in rice. The overall research method is secondary data analyses using visual analytics techniques implemented through Tableau Software. Several datasets were utilized to conduct visual analytical representations of data on arsenic concentrations in foods. These consisted of (i) arsenic concentrations in 459 crop samples; (ii) arsenic concentrations in 328 table ready foods from multi-year total diet studies; (iii) estimates of daily inorganic arsenic intake for 49 food groups from multicountry total diet studies; (iv) arsenic content in rice product categories for 193 samples of rice and rice products; (v) 758 sentences extracted from PubMed abstracts on arsenic in rice. Several key insights were made in this doctoral research. The concentration of inorganic arsenic in instant rice was lower than those of other rice types. The concentration of Dimethylarsinic Acid (DMA) in wild rice, an aquatic grass, was notably lower than rice varieties (e.g. 0.0099 ppm versus 0.182 for a long grain white rice). The categorization of 328 table ready foods into 12 categories enhances the communication on arsenic concentrations. Outlier concentration of arsenic in rice were observed in views constructed for integrating data from four total diet studies. The 193 rice samples were grouped into two groups using a cut-off level of 3 mcg of inorganic arsenic per serving. The visual analytics views constructed allow users to specify cut-off levels desired. A total of 86 sentences from 53 PubMed abstracts were identified as informative for arsenic concentrations. The sentences enabled literature curation for arsenic concentration and additional supporting information such as location of the research. An informative sentence provided global “normal” range of 0.08 to 0.20 mg/kg for arsenic in rice. A visual analytics resource developed was a dashboard that facilitates the interaction with text and a connection to the knowledge base of the PubMed literature database. The research reported provides a foundation for additional investigations on visual analytics of data on arsenic concentrations in foods. Considering the massive and complex data associated with contaminants in foods, the development of visual analytics tools are needed to facilitate diverse human cognitive tasks. Visual analytics tools can provide integrated automated analysis; interaction with data; and data visualization critically needed to enhance decision making. Stakeholders that would benefit include consumers; food and health safety personnel; farmers; and food producers. Arsenic content of baby foods warrants attention because of the early life exposures that could have life time adverse health consequences. The action of microorganisms in the soil is associated with availability of arsenic species for uptake by plants. Genomic data on microbial communities presents wealth of data to identify mitigation strategies for arsenic uptake by plants. Arsenic metabolism pathways encoded in microbial genomes warrants further research. Visual analytics tasks could facilitate the discovery of biological processes for mitigating arsenic uptake from soil. The increasing availability of central resources on data from total diet studies and research investigations presents a need for personnel with diverse levels of skills in data management and analysis. Training workshops and courses on the foundations and applications of visual analytics can contribute to global workforce development in food safety and environmental health. Research investigations could determine learning gains accomplished through hardware and software for visual analytics. Finally, there is need to develop and evaluate informatics tools that have visual analytics capabilities in the domain of contaminants in foods.
Environmental Sciences
P. Phil. (Environmental Science)

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.

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.

The mixed metal compound, Chromated Copper Arsenate, or CCA, has been widely used as a wood preservative. The metal ions in CCA, CrO��������, Cu�����, and AsO��������, have been found in contaminated surface and subsurface soils and groundwater nearby some wood preservative facilities and nearby wood structures. Iron oxides are a ubiquitous soil-coating constituent and are believed to be a main factor in controlling the transport and fate of many metals in the soil solution. In this research, iron-oxide-coated sand (IOCS) is used as a surrogate soil to investigate the adsorption and transport behavior of the mixed metals solution, copper, chromate, and arsenate, in the subsurface environment. Copper adsorption increases with increasing pH. The presence of arsenate in the solution slightly increases, while chromate has minimal effect, on the amount of copper adsorbed. Chromate adsorption decreases with increasing pH. With arsenate present in solution, chromate adsorption is significantly suppressed over the pH range studied. In contrast, the presence of copper slightly increases chromate adsorption. Similar to chromate, arsenate adsorption decreases with increasing pH. The presence of chromate or copper does not affect the amount of arsenate adsorbed over the range of concentrations studied. Two surface complexation models, the triple layer model (TLM) and the electrostatic implicit model (EIM), were used to simulate equilibrium adsorption in both single-metal and multi-metal systems. Simulations using the specific surface complexation equilibrium constants derived from either the single-metal or the multi-metal systems with both the TLM and the EIM were successful in fitting the adsorption data in that respective single or multi-metal system. The local equilibrium assumption using batch-derived sorption isotherm parameters from the EIM failed to predict the copper and arsenate transport, while it adequately described chromate transport. The breakthrough curves of all three metals were asymmetrical and showed long-tailing behavior. This nonideal behavior is caused by nonlinear sorption and/or non-equilibrium conditions during transport. The two-site chemical non-equilibrium model, which accounts for the kinetically controlled adsorption sites, was able to fit the observed breakthrough curves for all three metals in single-metal systems. However, the model was partially successful in predicting transport in multi-metal systems.
Graduation date: 2002