Browsing by Subject "Arsenic"
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Item Adsorption, desorption, and stabilization of arsenic on aluminum substituted ferrihydrite(Texas A&M University, 2006-04-12) Masue, YokoBecause of As toxicity, the complexity of its chemistry, and the recent lowering of the maximum contaminant level of As in municipal drinking water, there has been considerable interest for improved methods to remove As from water. Although Al and Fe hydroxides have been extensively studied as adsorbents for As removal during water treatment, coprecipitated Al:Fe hydroxides have received only minimal attention. The theoretical and experimental feasibility of coprecipitated Al:Fe hydroxide systems were evaluated by studying their mineralogy, stability, and As adsorption and desorption behavior. The broad XRD peaks revealed that Al was substituted into the ferrihydrite structure and that this was the only major product up to about a 2:8 Al:Fe molar ratio. Gibbsite and bayerite were identified when Al content was higher. The rate of recrystallization of ferrihydrite into goethite and hematite was significantly reduced as Al substitution was increased. In general, adsorption capacity of both AsV and AsIII decreased with increase in Al:Fe molar ratio; however, similar AsV adsorption capacities were observed with Fe and Al:Fe hydroxides with Al:(Al+Fe) molar ratios < 0.20. Both AsIII and AsV adsorption isotherms were effectively described by Langmuir and Freundlich equations. Adsorption maxima of AsV on Fe and Al:Fe hydroxides were observed at pH 3 to 7, and that of AsV on Al hydroxide was observed at pH 5.2, with significant decreases in adsorption with increase and decrease in pH. Adsorption maxima of AsIII decreased by approximately 4 % for each 10 % increase in Al substitution up to 5:5 Al:Fe molar ratio. Adsorption maxima of AsIII on Fe and Al:Fe hydroxides were observed at pH 8 to 9. AsIII adsorption on Al hydroxide was negligible. Counterion Ca2+, compared to Na+, enhanced the retention of AsV, especially at pH > 7. Counterion concentration did not significantly affect AsV adsorption. Though phosphate desorbed both AsV and AsIII from all Al:Fe hydroxides, quantitative desorption was never observed. The results of this study indicate the possible utility of coprecipitated Al:Fe hydroxide in wastewater treatment. Based on adsorption/desorption behavior and stability of the Al:Fe hydroxide product, the preferred Al:Fe molar ratio was 2:8.Item Archaea at the El Tatio Geyser Field : community composition, diversity, and distribution across hydrothermal features and geochemical gradients(2012-05) Franks, Megan A.; Bennett, Philip C. (Philip Charles), 1959-; Bell, Christopher J.; Cardenas, Meinhard B.; Engel, Annette S.; Hawkes, Christine V.Methanogenesis, a metabolic pathway unique to Archaea, is severely inhibited by the reduced form of arsenic (As). Despite this inhibition, methanogenic Archaea are present in some hydrothermal features at the El Tatio Geyser Field (ETGF), a high-arsenic site with 100+ hydrothermal features, including boiling pools, geyers, fumaroles, and springs. The ability of methanogenic Archaea and other microorganisms to withstand elevated arsenic concentrations, and a variety of other extreme environmental conditions at ETGF, may be due to unique adaptations or syntrophic relationships with other microorganisms. ETGF is situated in the Andes Mountains at an altitude of ~4300 meters. UV radiation is elevated in this region and air temperatures fluctuate widely. Most hydrothermal waters discharge at ~85˚C, the local boiling point, and rapidly evaporate due to the arid climate. This concentrates hydrothermal salts and metals, including arsenic (As) and antimony (Sb). Additionally, dissolved inorganic carbon (DIC) concentrations are extremely low in most features and may limit life. Water chemistry analyses done for this study show variability in dissolved constituents between features that are consistent over time. Variations may be due to the source or residence time of waters, and differences in chemistry could be responsible for the presence or absence of methanogenic Archaea at hydrothermal sites. The overlying control on microbial diversity and community composition may be water geochemistry, and potentially specific constituents. The goals of this study were to detect novel microbial taxa at ETGF, including novel methanogens, as well as to document microbial community composition at select hydrothermal features. The distribution and diversity of microorganisms at each feature was analyzed phylogenetically and within an ecological context in order to determine physicochemical and biological controls on community composition. Additionally, a model methanogen was used in laboratory analyses to determine how concentrations and oxidation states affected growth and methane production. This methanogen, Methanothermobacter thermautotrophicus, is found at ETGF, Yellowstone, and other hydrothermal fields, and thrives in high-temperature environments. MPN (most probable number) analyses show that culturable biomass from multiple sites contain metabolically active methanogens. These results support the biogenicity of dissolved methane detected in the field. 16S rRNA surveys of Archaea at four sites show that Archaea are diverse, and archaeal community composition varies across features. Phylogenetic tree construction indicates that Archaea from ETGF group together, suggesting that the isolation and broad environmental constrains on ETGF have some control on phylogenetic diversity. Laboratory analyses of As and Sb concentrations on M. thermautotrophicus suggest that Sb may decrease the inhibition of methanogenesis by As by preventing the formation of As(III) from As(V). Statistical analyses correlating microbial community composition and structure to physicochemical parameters show that archaeal and bacterial communities relate to different variables; with Bacteria correlating to water temperature, and Archaea correlating to dissolved constituents such as hydrogen gas and sulfate.Item Arsenate uptake, sequestration and reduction by a freshwater cyanobacterium: a potenial biologic control of arsenic in South Texas(Texas A&M University, 2005-08-29) Markley, Christopher ThomasThe toxicity and adverse health effects of arsenic are widely known. It is generally accepted that sorption/desorption reactions with oxy-hydroxide minerals (iron, manganese) control the fate and transport of inorganic arsenic in surface waters through adsorption and precipitation-dissolution processes. In terrestrial environments with limited reactive iron, recent data suggest organoarsenicals are potentially important components of the biogeochemical cycling of arsenic in near-surface environments. Elevated arsenic levels are common in South Texas from geogenic processes (weathering of As-containing rock units) and anthropogenic sources (a byproduct from decades of uranium mining). Sediments collected from South Texas show low reactive iron concentrations, undetectable in many areas, making oxy-hydroxide controls on arsenic unlikely. Studies have shown that eukaryotic algae isolated from arsenic-contaminated waters have increased tolerance to arsenate toxicity and the ability to uptake and biotransform arsenate. In this experiment, net uptake of arsenic over time by a freshwater cyanobacterium never previously exposed to arsenate was quantified as a function of increasing As concentrations and increasing N:P ratios. Toxic effects were not evident when comparing cyanobacterial growth, though extractions indicate accumulation of intracellular arsenic by the cyanobacterium. Increasing N:P ratios has minimal effect on net arsenate uptake over an 18 day period. However, cyanobacteria were shown to reduce arsenate at rates faster than the system can re-oxidize the arsenic suggesting gross arsenate uptake may be much higher. Widespread arsenate reduction by cyanobacterial blooms would increase arsenic mobility and potential toxicity and may be useful as a biomarker of arsenic exposure in oxic surface water environments.Item Development of new automated flow titration systems(Texas Tech University, 2004-08) Jo, Kyoo DongTitrimetry is one of the oldest analytical methods still in use. It is probably the analytical technique that has changed the least over the years. It remains one of the most widely used tools for making high precision measurement. In classical batch mode titration procedures, the volume of titrant added to a titration vessel is the variable that is controlled and monitored and subsequently used to calculate the original analytical concentration in the test solution. More advanced and automated batch mode titrators have been developed. However, the downside of titrations in conventional batch mode are significant reagent consumption and poor throughput rate. Thus, automation of titrations using the continuous flow mode has been increasingly drawing attention. The new concept for continuous on-line titrations based on feedback-controlled flow-ratiometry and the principle of compensating errors creates a new paradigm for flow titrations by feedback based flow ratiometry in which the delay between the sample-titrant confluence point and the detector is made constant. The error due to lag time is continuously compensated for by averaging rapid backward and forward titrations. This new concept has been developed and applied to titrations followed by potentiometry and photometry. Electrogeneration of titrants have several significant advantages. The most important of these is the elimination of problems associated with the preparation, standardization, and storage of titrant solutions. This advantage is particularly significant when dealing with unstable reagents. Electrogeneration of the titrant allows the transformation of the newly developed error-compensated feedback based flow-gradient method into a concentration gradient method. Coulometric titrant generation transfers the control from the flow control to current control. This system has been applied to various redox titrations using photometric and potentiometric detection methods. An additional new type of flow injection titration system has been developed based on a syringe pump. In this system, the titrant is injected in a triangular programmed flow pattern by a syringe pump in a continuous stream of the sample. This new type of flow injection titration method was applied to acid-base and redox titrations, and the data interpreted by the principle of compensating errors.Item Dopant behavior in complex semiconductor systems(2009-12) Kong, Ning; Kirichenko, Taras A.; Banerjee, SanjayAs the size of modern transistors is continuously scaled down, challenges rise in almost every component of a silicon device. Formation of ultra shallow junction (USJ) with high activation level is particularly important for suppressing short channel effects. However, the formation of low resistance USJ is made difficult by dopant Transient Enhanced Diffusion (TED) and clustering-induced deactivation. In this work, we proposed a novel point defect engineering solution to address the arsenic TED challenge. By overlapping arsenic doped region with silicon interstitials and vacancies, we observed enhanced and retarded arsenic diffusion upon anneal, respectively. We explain this phenomenon by arsenic interstitial diffusion mechanism. In addition, we implemented this interstitial-based mechanism into a kinetic Monte Carlo (kMC) simulator. The key role of interstitials in arsenic TED is confirmed. And we demonstrated that the simulator has an improved prediction capability for arsenic TED and deactivation. As a long time unsolved process challenge, arsenic segregation at SiO₂/Si interface was investigated using density functional theory (DFT) calculation. The segregation-induced arsenic dose loss not only increases resistance but also may induce interface states. We identified three arsenic complex configurations, [chemical formula] , [chemical formula] and [chemical formula], which are highly stabilized at SiO₂/Si interface due to the unique local bonding environments. Therefore, they could contribute to arsenic segregation as both initial stage precursors and dopant trapping sites. Our calculation indicates that arsenic atoms trapped in such interface complexes are electrically inactive. Finally, the formation and evolution dynamics of these interface arsenic-defect complexes are discussed and kMC models are constructed to describe the segregation effects. A potential problem for the p-type USJ formation is the recently found transient fast boron diffusion during solid phase epitaxial regrowth process. Using DFT calculations and molecular dynamics simulation, we identified an interstitial-based mechanism of fast boron diffusion in amorphous silicon. The activation energy for this diffusion mechanism is in good agreement with experimental results. In addition, this mechanism is consistent with the experimentally reported transient and concentration-dependent features of boron diffusion in amorphous silicon.Item Fate and transport of arsenic and antimony in the El Tatio Geyser Field, Chile(2007-05) Landrum, Jeffrey Thomas, 1979-; Bennett, Philip C. (Philip Charles), 1959-El Tatio Geyser Field (ETGF), northern Chile, hosts widespread geothermal activity, with very high aqueous concentrations of arsenic and antimony, higher than any other known geothermal system. Boiling springs (86°C) discharge circum-neutral pH, Na-Cl type waters with low organic carbon. Net discharge of a stream draining the ETGF basin is approximately 10 cfs. As(III), the dominant As species in discharge waters, rapidly oxidizes to As(V) at an estimated first order rate of 0.35 min-1, determined in the field by first arrival of a tracer. As and Sb concentrations and speciation in hydrothermal waters, deposits, and microbial biomass are evaluated as a product of microbial metabolism, sorption to metal-oxyhydroxides, and co-precipitation. Mechanisms controlling these reactions ( i.e. cooling, evaporation, changes in redox and pH) are evaluated and modeled. Sequential extractions reveal that As, sorbs to Fe and Mn oxy-hydroxide complexes. In contrast, Sb solid phase partitioning is influenced primarily by the co-precipitation of Sb-oxide minerals with siliceous sinter (up to 2% wt. Sb). Diurnal variations occur in spring water chemistry and may cause Sb-rich laminations in siliceous hydrothermal deposits. Microbial energetics calculations and enrichment experiments suggest that microbial activity influences the mobility of As, and probably Sb in the ETGF basin by altering redox speciation and sorption to microbial biomass.Item Ferrihydrite as an Enterosorbent for Arsenic(2012-02-14) Taylor, John FloydArsenic in drinking water is a problem in many developing nations such as Taiwan and Bangladesh. Currently, no oral binding agent exists for the mitigation of arsenic toxicity. The goals of this research were to 1) screen a variety of sorbents for their ability to sorb As from water and screen for potential nutrient interactions with vitamin A (VA) and riboflavin (RF) isotherms; 2) further describe the sorption of As to ferrihydrite using isothermal analysis and a simulated gastrointestinal model (GI), and by testing ferrihydrite?s ability to protect Hydra from As toxicity; 3) verify ferrihydrite?s safety and efficacy in a short term rodent model. Ferrihydrite was found to be the most effective sorbent for both As(III) and As(V). Exchanging SWy-2 with sulfur containing organic groups increased the sorption of both As(V) and As(III) compared to the parent clay, though the total As sorbed was much less than As sorption by ferrihydrite. Ferrihydrite and an industrially produced ferrihydrite (IPF) both sorbed As(V) and As(III) with high capacity. Both ferrihydrites also sorbed As(V) and As(III) at high capacity in the simulated GI model. Fe measured in the simulated GI tract was below tolerable daily limits for both ferrihydrite and IPF. Ferrihydrite at 0.25 percent w/w was found to protect Hydra up to 200 times the minimal effective concentration (MEC) for As(III) and over 2.5 times the MEC for As(V), while IPF at 0.25 percent w/w protected Hydra up to 200 times the MEC for As(III) and just over 2 times the MEC for As(V). IPF was apparently safe and well tolerated by the rats in our study over a period of 2 weeks. No statistically significant differences were seen in serum biochemistry, serum Fe, serum VA, or serum vitamin E between rats fed control diet versus those fed 0.5 percent w/w IPF. Ferrihydrite was found to reduce urinary As after a single gavage of 0.5 mL of 500 ppm As(III) or As(V). These results verify in vitro findings and suggest that ferrihydrite is apparently safe and effective as an enterosorbent for As.Item First principles modeling of arsenic and fluorine behavior in crystalline silicon during ultrashallow junction formation(2006) Harrison, Scott Anthony; Hwang, Gyeong S.; Edgar, Thomas F.Item Heavy metal and arsenic bioaccumulation in small mammals inhabiting the Anaconda Smelter Superfund Site, Montana(Texas Tech University, 2004-08) Reynolds, Kevin D.A key component in accurately assessing bioavailability of environmental metals at large National Priority List (NPL) sites is a reduction of uncertainty within exposure estimates. This reduction in uncertainty can be facilitated by collecting empirical data from individual animals inhabiting hazardous waste sites. Site-specific metal bioavailability data are also useful in supporting decisions regarding clean up and demediation, and regulators and scientists also support the use of these data in their exposure assessment models. However, rarely are data available to confirm modeled results. The primary objective of this study was quantifying the site-specific bioavailability and accumulation of heavy metals and arsenic in small mammals inhabiting a metals-contaminated NPL hazardous waste site in southwest Montana Deer mice (Peromyscus maniculatus) and northern pocket gophers (Thomomys talpoides) inhabiting areas contaminated with a gradient of heavy metals and arsenic were collected from the Anaconda Smelter SuperfUnd Site, Montana, USA. A total of 299 deer mice were collected in 1999 and 2000. Arsenic (As), cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn) were determined in blood, kidney, liver, mammary tissue, carcass, and stomach contents and compared to metal levels in the soils across six respective trapping grids established on spontaneously revegetated areas of the site. Among deer mouse stomach contents and tissues, only Zn and Cu were detected with regularity in all tissues. Lead and As were detected primarily in carcass samples, and Cd was detected most frequently in liver and kidney samples. Among all tissues analyzed, there were no differences (p > 0.05) between male and female mice for any of the metals except for Pb. When all mice were grouped by sex, there was a larger (p = 0.0380) proportion of female liver samples with detectable concentrations of Pb compared to males. Differences between adult and nonadult mice were mostly observed for Pb, Cd and As concentrations in kidney, liver and carcass samples.Item Heavy Metals in Glass Beads Used in Pavement Markings(2012-07-16) Mangalgiri, KiranmayiPavement markings are vital for safely navigating roadways. The nighttime visibility of pavement markings is enhanced by addition of retroreflective glass beads, most of which are made from recycled glass. Concern has been raised over the presence of heavy metals in glass beads used in pavement markings and their effect on human and environmental health. Based upon the potential risk associated with the presence of arsenic and lead in the glass beads, two Bills are currently being considered before the 112th Congress of the United States of America seeking to set a maximum permissible limit for the amount of arsenic and lead in glass beads used within pavement marking systems on domestic roadways. This study was designed to support legislative decision making by providing data necessary for risk assessment. The experiments carried out provide: an analysis of glass bead metal content and extractability; an evaluation of the relationship between arsenic content of the glass beads and their retroreflective performance; an evaluation of analytical methods used to measure the total bead metal content; and an analysis of samples of glass bead and soil mixture from a glass bead storage site used to determine site-specific metal concentrations in the soil media. Mean arsenic content, measured using the Pacific Northwest National Laboratory's KOH fusion digestion, in all the glass beads examined ranged from 11 ppm to 82 ppm, while mean lead content, measured using KOH fusion digestion, ranged from below quantification limit to 199 ppm. Total metal content measurements indicated a high amount of variability in the glass bead samples; most likely associated with the use of recycled glass feed during manufacturing. The relationship between the retroreflective performance and the arsenic content of the glass beads was analyzed and a weak but positive correlation was observed between the two factors. However, a more detailed study is required to evaluate the relationship between arsenic content and retroreflectivity. Different methods to evaluate the total metal content in glass beads were compared; it is recommended that any analytical method may be used, as long as the standard reference material is reproduced within the range of concentration expected in the glass beads. In the analysis of the field site samples of soil containing glass beads obtained from a glass bead storage and transfer facility, the mass content of beads in the soil varied from a mean of 19% to 78% depending on the location within the facility. However, a detailed analysis with larger number of samples must be performed to evaluate the effect of glass beads on the total arsenic content of the soil.Item In Situ Groundwater Arsenic Removal Using Iron Oxide-Coated Sand(2010-10-12) Yu, HongxuIn many regions of the world, groundwater is contaminated with a high level of arsenic that must be treated before it can be safely used as drinking water. In situ immobilization of arsenic from groundwater within subsurface environment could have major advantages over the conventional above-ground chemical coagulation-precipitation treatment process. In this study, we develop a novel technique that can in situ emplace iron oxides onto the sand grain surface of porous media under mild chemical and temperature conditions. The technique involves sequential injections of a preconditioned ferrous iron solution and an oxidant solution and then orchestrate the advective-diffusive transport of the two reagents in porous media to create an overlapped reaction zone where ferrous iron is oxidized and precipitated on the sand grain surfaces. We demonstrate through bench-scale column tests the feasibility of using this technique to create a large-scale iron oxide-enriched reactive barrier in subsurface environment for in situ removal of arsenic. A sand filter with a fresh iron oxide coating can treat thousands of pore volumes of water contaminated with dozens of ppb arsenic before the coating needs to be regenerated. Arsenic breakthrough curves through the sand filter suggest that both reversible adsorption and irreversible precipitation are responsible for removing arsenic from the water. Unlike conventional excavate-and-fill permeable reactive barriers, the treatment capacity of our in situ created barrier can be in situ regenerated and replenished with a fresh coating.Item Influence of metal mixtures on co-occurring toxic metal bioavailability and effects in adult and developing deer mice(Texas Tech University, 2007-12) McBride, Tobias J.; Hooper, Michael J.; McMurry, Scott T.; Cox, Stephen B.; Hoff, Dale J.The bioaccessibility, bioavailability, and bioaccumulation of inorganic metals are complex principles. Unlike organic xenobiotics, many metals are required for biological functions. Nonetheless, dramatically increased concentrations of any metal may interact adversely with biomolecules, initiating a toxicological response when above a certain concentration in the organism. The bioavailability of environmental metals depends not only on metal concentrations in relevant matrices (food, water, soil), but on the chemical/physical form in which metals occur, the concentrations of other metals which co-occur, and the physiological status of the individual. Studies of mixed metal and metalloid (As, Cd, Cu, Pb and Zn) exposure in deer mice (Peromyscus maniculatus) at the Anaconda Smelter Site demonstrated that accumulation and biomarkers did not respond to the extent anticipated based on individual metal levels alone. This dissertation focuses on factors influencing the uptake, accumulation and resultant health effects of inorganic metals in a ubiquitous wild rodent species, and attempts to explain results from an earlier wildlife assessment on an NPL Superfund site. We sought to explain the variability in the effects of Pb exposure seen with the extreme heterogeneity of co-occurring metal contaminants in site soils. Using soil feeding studies, we have dissected the roles of Cu and Zn in modulating Pb absorption and Zn's role in reactivating ALAD activity in mice receiving high Pb doses. Second, our focus involves a lifetime bioaccumulation study of mice that investigated lactational metal exposure through the first 21 days of life (from soil-dosed feed provided to dams), and follows accumulation through 100 days of life. Comparisons with studies where adult mice were fed soil metals in their diet demonstrated that the more realistic lifetime exposure approach changes the accumulation kinetics, leading to greater accumulation of Cd and As, while underestimating exposures to Pb in the younger individuals. Finally, we investigate the role of lactation in weanling metal bioaccumulation, demonstrating how lactation decreases the dam's metal accumulation, while significantly increasing As and Pb exposure risks to the developing young.Item Measurement of arsenic in water and soil based on gas-phase chemiluminescence(Texas Tech University, 2007-05) Idowu, Ademola David; Dasgupta, Purnendu K.; Liu, Shaorong; Quitevis, Edward L.Arsenic occurs widely in nature and is a known human carcinogen. Developmental, immunological, and neurological defects are linked with chronic exposure to arsenic in drinking water. The United States Environmental Protection Agency (US EPA) prescribed safe limit is 10 μg/L. Standard atomic spectrometry based methods are expensive. Field wet techniques require large amounts of acid, other reagents and paper strips impregnated with toxic mercury and lead compounds. This dissertation presents a new, fast, safe, affordable automated system configurable for laboratory or field use. Arsenic in the sample is chemically or electrochemically reduced to arsine that reacts with ozone atop a photomultiplier tube, producing chemiluminescence. Direct chemical, electrochemical, and liquid chromatography methods are described. The first method uses sodium borohydride for the reduction of arsenic. Differential determination of arsenate and arsenite is based on the different pH dependence on their conversion to arsine. At pH ≤1, both arsenate and arsenite are quantitatively converted. At pH 4-5, only arsenite is converted. Under these conditions, limit of detection (LOD) is 0.05 and 0.09 μg/L for total arsenic and arsenite, respectively, with a 3-mL water sample. The relative standard deviation for 3 determinations was 1.2 and 2.1% for 1 μg/L total arsenic and arsenite respectively. The arsenic concentrations in this dissertation are all based on that of elemental arsenic. The Electrochemical method uses a Platinum screen anode and stainless steel cathode in two compartments, separated by a Nafion membrane. Arsenite is selectively reduced on a stainless steel cathode while a cadmium-coated cathode reduces both forms. The limit of detection is 1.5 and 4 μg/L for arsenite and total arsenic respectively with a 2-mL water sample. The relative standard deviation for 3 determinations was 2.6 and 4.5% for 10 μg/L arsenite and total arsenic respectively. This environment-friendly method uses only re-usable sulfuric acid electrolyte, air, water and electricity but requires further development. Arsenite, arsenate, dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) are separated on anion-exchange column using carbonate and hydroxide eluents. Separated species are photolytically oxidized by UV-light, converting organic species to their respective inorganic forms. Subsequent online reaction with acid and borohydride produces arsine, detected by CL. For arsenite, arsenate, MMA and DMA the LOD is 0.4, 0.2, 0.5 and 0.3 μg/L respectively for a 100-μL injected sample. The relative standard deviation for 3 determinations was 3.5, 2.8, 2.2, and 4.1% for 10 μg/L of each of arsenite, arsenate, MMA, and DMA respectively. The system has been tested successfully on water and soil samples, and can be adapted for matrices such as biological samples and body fluids. There are no significant practical interferencesItem The microbial ecology and biogeochemistry of cyanobacteria in the arsenic-rich and inorganic carbon-limited geothermal waters of El Tatio Geyser Field, Chile(2015-05) Myers, Kimberly Dawn; Bennett, Philip C. (Philip Charles), 1959-; Bell, Christopher J; Omelon, Christopher R; Shanahan, Timothy M; Hawkes, Christine VGeothermal settings are some of the best-known analogs for early earth environments and among the best places to investigate the impact of extreme conditions on microbial life. El Tatio Geyser Field (ETGF) is a geothermal setting located at 4,300m in the Atacama Desert region of Chile. Its high-elevation desert position leads to high UV-flux, rapid evaporation, and mineral precipitation. El Tatio geothermal waters also possess extremely limited concentrations of life-essential nutrients, such as dissolved inorganic carbon (DIC as CO2(aq) + HCO3-), contain among the highest naturally occurring concentrations of the toxic element arsenic (As as H3AsO30 + HXAsO43-X), and are buffered to circumneutral pH by arsenate (H2AsO4-/HAsO42-; pKa ~ 6.9 at 25°C). Cyanobacteria were found to be the most important primary producers supporting microbial communities in El Tatio geothermal waters. The objective of this dissertation work was to characterize the role of cyanobacteria in the ETGF microbial ecosystem, and determine the response of cyanobacteria to the high-As and low-DIC conditions present at ETGF. Field observations, geochemical analyses, and next-generation 16S rRNA gene sequencing approaches were used to determine the geochemical controls on cyanobacterial distribution, the phylogenetic diversity of El Tatio cyanobacteria, and the corresponding microbial community structure at sites with and without cyanobacteria. Four cultured cyanobacterial strains were isolated from ETGF mat material, and experiments were performed to assess the growth and carbon-uptake response of these strains to low DIC, AsIII, and AsV. AsIII and temperature negatively controlled the abundance and distribution of cyanobacteria in geothermal outflows throughout ETGF, whereas AsV positively influenced these factors. In the laboratory, AsIII inhibited the growth of cultured strains, while AsV stimulated growth. Closed-system experiments showed significantly increased carbon uptake and growth in the presence of AsV, due to the ability of arsenate to offset the rapid upward pH shift that often occurs in mats during photosynthesis, thereby maintaining DIC in the preferred forms for cyanobacterial uptake. These results showed that AsV plays a positive role in the ETGF microbial ecosystem by increasing the productivity of cyanobacterial mats under low DIC and arsenate-buffered conditions.Item Occurrence, Distribution, And Speciation of Arsenic in the Southern High Plains Aquifer System(2010-12) Venkataraman, Kartik; Rainwater, Ken; Jackson, Andrew W.; Ridley, Moira K.Significant levels of arsenic have been detected in the groundwater of the Southern High Plains. The potential sources include atmospheric deposition, the use of agricultural defoliants and natural subsurface geochemical interactions. To identify the source of arsenic, groundwater and soil samples were collected from sites spread over 18 counties in the Southern High Plains. Total arsenic and its inorganic species were quantified along with commonly occurring and related cations and anions such as iron, manganese and sulfate. Correlation studies were conducted to understand the variation of arsenical species with related parameters. A geochemical modeling tool, MINTEQ was used to predict the speciation of arsenic and compare these results with lab analyses. The distribution of arsenic in the soil profiles tested indicated a positive correlation with depth. The highest concentrations were found close to the water table while the upper soil layers had low to non-detect concentrations. In the groundwater samples, arsenic concentration and speciation varied significantly between sites. As (III) was found to be the dominant species in over 80% of the samples. MINTEQ speciation forecasts compared favorably with a majority of the groundwater analyses. Very little evidence of atmospheric deposition exists and the sources of arsenic are likely anthropogenic land sources in the shallow subsurface and natural geologic processes in the deeper subsurface.Item Sorption of Arsenic, Mercury, Selenium onto Nanostructured Adsorbent Media and Stabilization via Surface Reactions(2011-02-22) Han, Dong SukThe overall goal of this study is to evaluate the ability of novel nanostructured adsorbent media (NTAs, iron sulfides (FeS2 and FeS)) to remove arsenic, selenium and mercury from ash and scrubber pond effluents. The NTAs aim to enhance arsenic removal from solution compared to conventional adsorbents. The iron sulfides are expected to produce stable residuals for ultimate disposal after removing As, Se and Hg from solution, so that removal of these compounds from wastewaters will not result in contamination of soils and groundwaters. Methods for reliably and economically producing these materials were developed. The synthesized NTAs and iron sulfides were characterized by surface analysis techniques such as XRD, FT-IR, SEM-EDS, TEM, XPS, AFM and N2-adsorption. These analyses indicated that Ti(25)-SBA-15 has highly ordered hexagonal mesopores, MT has interparticle mesopores, pyrite (FeS2) forms crystalline, nonporous rectangular nanoparticles (<500 nm), and mackinawite (FeS) forms amorphous, nonporous nanoparticles (<100 nm). Kinetic and equilibrium tests for As(III, V) removal were conducted with NTAs over a range of pH (4, 7, 9.5). The rates of arsenic uptake were very fast and followed a bi-phasic sorption pattern, where sorption was fast for the first 10 minutes, and then slowed and was almost completed within 200 minutes. Distinct sorption maxima for As(III) removal were observed between pH 7 and pH 9.5 for MT and between pH 4 and pH 7 for Ti(25)-SBA-15. The amount of As(V) adsorbed generally decreased as pH increased. In addition, a surface complexation model (SCM) based on the diffuse layer model (DLM) was used to predict arsenic adsorption envelopes by NTAs under various environmental conditions. The SCM for As(III, V) adsorption by NTAs demonstrated the role of mono- and bidentate surface complexes in arsenic adsorption. A batch reactor system was employed in an anaerobic chamber to conduct experiments to characterize both the removal of As, Se, Hg from solution and their subsequent reactions with iron sulfides. Experiment variables for removal experiments included: contaminant valence state (As(V), As(III), Se(VI), Se(IV), Hg(II)); adsorbent/reactant type (FeS, FeS2); adsorbent/reactant concentration; pH (7, 8, 9, 10); and competing ion (SO42-) concentration (0, 1, 10 mM). Experimental variables for reaction experiments were reaction time (up to 30 days) at pH 8 and oxidation states of contaminants. In addition, the stability of iron sulfides (FeS2, FeS) combined with target compounds was investigated by measuring the ability of the target compounds to resist release to the aqueous phase after removal. These experiments showed that iron sulfides were good adsorbent/reactants for target contaminants in spite of the presence of sulfate. This was particularly true at intermediate concentrations of target compounds. The experiments also demonstrated that iron sulfides interacted with target contaminants in such a way to improve their resistance to being released back to solution as pH was changed. Therefore, this study demonstrates the ability of novel nanostructured adsorbent media to remove arsenic, selenium and mercury from ash and scrubber pond effluents and the ability of iron sulfides to produce residuals that are stable when disposed in landfills.Item The amelioration of arsenic toxicity in Fischer 344 rats supplemented with selenite in the diet(Texas Tech University, 2002-08) Henderson, Lora SuzannePrior to the early 1970s, the people in rural areas of Bangladesh and West Bengal, India, where sanitary drinking water is scarce, had no ahemative to drinking severely polluted surface water (Henry 1990). During the 1970s, United Nations Intemational Children's Fund (UNICEF) fimded the digging of tube wells, which were to supply clean drinking water to the people from underground sources (Guha Mazumder 1998). In 1993, 10-20 years after the first wells were dug, people began developing unusual symptoms: hyperpigmentation of the skin on unexposed areas of the body, thickening of the pahns of the hands and soles of the feet, skin lesions (both malignant and benign), and ahered hver, nerve, gastrointestinal, and/or lung fiinction (Guha Mazumder 1998). These symptoms are all characteristic of chronic arsenic (As) toxicity. Testing water samples from the tube wells determined the water contained levels of As from less than 3 ppb, which is virtuaUy arsenic free, to over 1000 ppm (Chowdhury 2000), well above the tolerable hmits set by World Heahh Organization (WHO) (50 ppb) (Smith 2000). It has been estimated that 120 milhon people in Bangladesh and West Bengal have been exposed to unsafe levels (greater than or equal to 50 ppb) of As as a result of obtaining it in the drinking water from these wells (Chowdhury 2000). Attempting to alleviate the situation, WHO has ftinded many research projects (Anstiss 2001), mcluding those designed to remove As from the water, cheaply and effectively, as well as projects aimed at counteracting As toxicity in vivo. In the past, research has shown that As may amehorate selenium (Se) toxicity (Levander 1966b); As may act synergistically with Se (Obermeyer 1971); or Se may counteract As toxicity (Babich 1989). The objective of this study was to determine if Se counteracts As toxicity in rats. The first phase of research was designed to detennine two effects: the tolerable upper limit (TUL) of As as 50% arsenite/ 50% arsenate in Fischer 344 rats and the effects of dietary Se supplementation on As toxicity. Fourteen groups of 6 rats were given 0, 25, 50, 100, 150, 175, or 200 ppm As in the water and 0.2 or lOppm Se in the food. After evaluating the data from the first phase, a second phase was conducted to determine a level of Se suitable for amehorating As toxicity in rats at the TUL (50 ppm). Nine groups of 6 rats were given 0 or 50 ppm As in the drinking water and either 0, 0.2, 1.25, 2.5, or 5ppm Se in their food. The Se deficient diet (0 ppm Se) was introduced to mimic a potential Se deficient diet in Bangladesh or West Bengal (J. SpaUholz, personal communication, March 27, 2002). This study provides insight into the effects of Se supplementation on As toxicity, as well as demonstrates the TUL of As in rats. Once analyzed and summarized, the results of this study will be beneficial to those conducting ftirther research in As toxicity.Item The Asiatic clam (Corbicula fluminea) as a bio-monitor for determining the distribution of antimony, arsenic and thallium in the water column and sediments of Manadas Creek, Laredo, Texas(Texas A&M International University, 2016-02) Garcia, Natasha; Vaughan, TomManadas Creek is an urban tributary of the Rio Grande that flows past a decommissioned antimony smelter. This smelter is associated with the heavy metal contamination in the creek and still poses a threat to the surrounding aquatic environment. With concerns on the rise of metal pollution, the biomonitor, the Asiatic clam (Corbicula fluminea) was used to determine bioaccumulation from the water column and sediments in Manadas Creek. The metals arsenic (As), antimony (Sb) and thallium (Tl) were analyzed in the water, sediments, gills, mantle, foot, digestive (DI) tract, gonads and shell of clams collected from sites between March to August 2013. Metal analysis of arsenic, antimony and thallium was performed by ICP-OES. High levels of antimony, arsenic and thallium in the water (13.45±6.65; 10.33±3.4; 7.47±1.73) and sediments (75.77±1.59; 6.41±1.19) at the site downstream from the smelter were observed. Additionally, tissue samples from this site had the highest concentrations, however there was no direct correlation between the metal concentrations in the water column and sediments with the tissues. There were no detectable concentrations of arsenic, antimony and thallium in shell samples. Site 3 had the highest thallium concentration in the sediments (3.00±0.68). No detectable thallium concentrations were detected in the tissues. Based on the results, the organotropism for arsenic is DI tract > gills > gonads > foot > mantle > shell and the organotropism for antimony is gills > DI tract > gonads > mantle > foot > shell. The Asiatic clam (Corbicula fluminea) is a useful biomonitor to provide data on the status of metal pollution in Manadas Creek, Laredo, Texas.Item The effect of arsenic trioxide on the grey flesh fly Sarcophaga bullata (Diptera: Sarcophagidae)(2011-05) Dacko, Nina M.; Presley, Steven; Cox, Stephen B.; Cobb, George P.Larvae of Sarcophaga bullata (Diptera: Sarcophagidae), a necrophagous insect commonly utilized in the field of entomotoxicology, were reared on rabbit tissues of rabbits that were previously exposed to arsenic trioxide (As2O3) by different methods. We observed the effects of arsenic (As) and As metabolites in acute versus chronic exposure in rabbit tissues on growth rate (mean larval length), metamorphosis, mortality and reproductive output of S. bullata. The New Zealand white rabbit was utilized as a vehicle to create natural concentrations of As and As metabolites in liver tissue and to serve as food media for S. bullata. Acutely exposed rabbits (2 per group) received three different doses of As2O3 corresponding to the dosages of half the median lethal dose or 0.5 MLD (10.1 mg/kg body weight (BW)), median lethal dose or MLD (20.2 mg/kg BW) and twice the median lethal dose or 2 MLD (40.4 mg/kg BW) and one control rabbit received dosing vehicle only. Chronically exposed rabbits received a dosage of 1.5 mg/kg BW daily for 35 days and one rabbit received dosing vehicle only. Rabbits were subsequently euthanized either eight hours post-exposure (acute) or on day 36 (chronic). The liver of these rabbits were removed and half was used as food media for 100 S. bullata larvae per experimental rabbit liver. The remaining half of the rabbit liver was used as a food media for 100 offspring of the prior experimental fly generation. Ten of these larvae were sampled and measured every eight hours until the onset of larval migration, for both generations of flies. Larval and pupal mortality was recorded, as well as the number of offspring, per dose group. ANOVA revealed a significant increase in mean larval body length in MLD as compared to the chronic dose group. Metamorphic time of S. bullata was positively correlated to the concentration of total As in exposed rabbit liver and mortality was negatively correlated to the concentration of total As in exposed rabbit liver. The reproductive output of S. bullata was not correlated to the concentration of total As in rabbit liver tissue.Item The modeling of arsenic removal from contaminated water using coagulation and sorption(Texas A&M University, 2005-11-01) Kim, Jin-WookTo achieve predictive capability for complex environmental systems with coagulation and arsenic sorption, a unified improved coagulation model coupled with arsenic sorption was developed. A unified coagulation model coupled with arsenic sorption was achieved by the following steps: (1) an improved discretized population balance equation (PBE) was developed to obtain the exact solution of conventional coagulation, (2) the improved PBE was extended to an adjustable geometric size interval having higher numerical stability, accuracy, and computational efficiency than existing models for fractal aggregate coagulation that includes agglomeration and fragmentation, (3) a surface complexation equilibrium model and a sorption kinetic model was introduced to predict arsenic sorption behavior onto hydrous metal oxide surfaces, and (4) an improved discretized PBE was coupled with arsenic sorption kinetics and equilibrium models by aid of collision efficiency ?? depending on surface charge (potential) on the hydrous metal oxide particles, colliding particle size ratio, and fluid strain-rate in applied flow system. The collision efficiency ?? into the improved (r,r)ij(r,r)ijdiscretized coagulation model for fractal aggregate yielded a unified improved coagulation model coupled with arsenic sorption kinetics and the equilibrium model. Thus, an improved unified coagulation model could provide high statistical accuracy, numerical stability, and computational efficiency to enhance predictive capability for behavior of arsenic sorption and fractal colloid particle aggregation and break-up, simultaneously. From the investigation, it is anticipated that the unified coagulation model coupled with arsenic sorption kinetics and equilibrium will provide a more complete understanding of the arsenic removal mechanism and its application to water/wastewater treatment. Further, this coupled model can be applied to other water and wastewater treatment systems combined with sorption and filtration processes. These combined processes can be optimized by the coupled model that was developed in this study. By simulating the arsenic sorption and particle size distribution as a pretreatment before filtration (sand filtration or membrane filtration), the overall arsenic removal efficiency and operation cost can be estimated.