A study of the transport properties of a substance requires the determination of a set of transport coefficients by experiment. From these coefficients, the elements of the electrical conductivity tensor, thermoelectric tensor, et cetera can be determined. In this experiment, measurements and analyses of galvanomagnetic effects in a single crystal of arsenic were performed. The measurements were made at liquid-helium temperatures in magnetic fields ranging to 25 kilogauss. The gross isothermal, electrical conductivities have been analyzed to determine various parameters characterizing the energy bands in arsenic.

The mobilization and transformation of arsenic within the critical zone is a major cause of human suffering worldwide. Microorganisms, as they grow and utilize organic matter, accelerate redox processes that can transform and mobilize arsenic within aquifers on a large scale. As such, naturally occurring groundwater arsenic is a particularly hazardous problem that is chronically poisoning over 100 million people annually. Historically, groundwater arsenic research has been focused on the two principal inorganic arsenic species: arsenate [As(V)] and arsenite [As(III)]. Recently, organic arsenic species have garnered more attention due to their mobility, toxicity, and contemporary recognition of the ephemeral yet significant role they have in the global arsenic cycle. Here, I discuss laboratory and in situ experiments focused on exploring how microorganisms transform, mobilize, and sequester arsenic within a biogeochemically complex aquifer system. In my laboratory experiments, I collected aquifer sediments from a naturally contaminated bedrock aquifer and incubated a series of laboratory microcosms. Our results show that simultaneously robust iron and sulfate reduction temporarily mitigated arsenic contamination but then directed arsenic to an unstable adsorbed phase were it was later mobilized. Second, I discuss two aquifer injection experiments designed to examine in situ microbial redox processes and the further explore the potential to stimulate arsenic sequestration through arsenic-sulfide precipitation. Our results show that in situ stimulation of microbial metabolisms accelerated the reduction of arsenic bearing iron (oxy)hydroxides as well as sulfate and arsenic reduction. Within 3 weeks of these contemporaneously occurring redox reactions, 90% of the dissolved inorganic arsenic was removed (~2000 ppb) and an effective long-term, anaerobically stable, sequestration of arsenic was observed by way of a significant increase of arsenic-sulfide precipitate. Finally, using both the laboratory and field experiments, I explore the potential of organic arsenic production rates under stimulated conditions. We report new methylation rates that are consequential to the potential efficacy of enhanced, biologically-driven arsenic remediation and the reconsidered significance of biomethylation pathways in aquifers. These results expand our current understanding of the metabolic reach aquifer microorganisms potentially have over the fate of arsenic.

Arsenic contamination of drinking water is a serious public health issue in many areas of South and South East Asia. One study estimates that in Cambodia over 100,000 people are exposed, with the majority of those living in Kandal Province. In this thesis we present 3 original empirical studies focused on estimating nonmarket values for reduced arsenic risk water, based on primary data collected in May 2013. We also present a review paper which discusses the various economic techniques which have typically been used to estimate welfare values for cost-benefit analysis of mitigation strategies or appraisal of drinking water standards. The first empirical paper presents the results of a discrete choice experiment (DCE)to estimate willingness to pay (WTP) values for reduced arsenic water. We discuss the results of scale-extended latent class choice models and underlying differences in preferences and choice consistency. We find that a reduction in the permissible limit on arsenic in drinking water may best represent underlying household preferences for risk. The second empirical paper presents the results of a split sample choice experiment focusing on differences between money (WTP) and labour contributions (WTWork) as payment vehicles in terms of choice behaviour and attribute non-attendance. We find that the results from the two experiments are relatively consistent which reinforces our results from the previous chapter that focuses on WTP measures alone and adds credibility to the large numbers of DCEs conducted in rural areas of developing countries. The final empirical paper examines actual household behaviour relative to an arsenic testing and education campaign run by a local NGO. We find that the vast majority of households change their drinking water source upon being informed that it is unsafe. On average households that switch increase their expenditures. In doing so however they also reduce the amount of time spent collecting water which limits the use of expenditure changes as an approximation of welfare values.

In Bihar state, India, the cure rate of antimonial compounds in the treatment of visceral leishmaniasis (VL) has declined from over 85% to less than 50%. This has been attributed to prolonged, widespread misuse of antimonials within the Indian private healthcare system. An alternative resistance hypothesis is that exposure to arsenic in drinking water in this region has resulted in antimony-resistant Leishmania parasites. Leishmania donovani were serially passaged in mice exposed to environmentally-relevant levels of arsenic in drinking water. Arsenic accumulation in organs of these mice was proportional to exposure. After five passages, isolated parasites were refractory to SbV in drug sensitivity assays. Treatment of infected mice with SbV confirmed that these parasites retained resistance in vivo, supporting this hypothesis. A retrospective field study on a cohort of antimony treated VL patients was performed in an arsenic contaminated area of Bihar to evaluate the presence of an increased risk of treatment failure and death in those exposed to arsenic. It demonstrated a significant increased risk of death from VL in arsenic exposed patients but did not indicate a significant relationship between arsenic exposure and antimonial treatment failure. Collectively these data suggest that it is biochemically possible that arsenic contamination may have contributed to the development of antimonial resistance in Bihar although issues of underpower and the retrospective nature of our epidemiological study made it difficult to conclusively demonstrate this. Further research in to the relationships between arsenic exposure and antimonial treatment failure and death in the leishmaniases is warranted.

Arsenic is found in the environment in several oxidation states as well as in a variety of organoarsenic compounds. This situation puts additional demands on the analysis in that it is desirable to measure the amount of each species, not just all of the arsenic. The reason for this is that the different species have greatly different toxicities; of the major inorganic forms, As(III) is much more toxic than As(V). The goal of this research was to develop a convenient method for the analysis of mixtures of As(III) and As(V) at trace levels. Electroanalytical methods are inherently sensitive to oxidation states of elements and therefore are a natural choice for this problem. In fact, a method was developed some years ago for As(III) that used differential pulse polarography: the detection limit is 0.3 parts per billion (ppb). However, As(V) was not detected since in its usual form as an oxyanion it is electrochemically inactive. There are coordinate compounds formed with catechol, AsL(,n)(n = 1-3), that can be reduced at a mercury electrode, but the active species, AsL, is only a small fraction of the major species, AsL(,3), so the detection limit is only 500 ppb. Many details of the electrochemistry of this unusual compound were examined in this work. In order to improve detection limits, a method involving cathodic stripping was developed. It involves codeposition of copper with arsenic on a mercury electrode to effectively concentrate the analyte. Then the elemental arsenic is converted to arsine, AsH(,3), during a cathodic potential scan. The resulting current peak is proportional to As(III) in the absence of catechol and to the sum of As(III) and As(V) in the presence of catechol. It was observed that the current peak was considerably larger than expected and additional experiments revealed that there was evolution of hydrogen during the formation of arsine. This is rather unusual in electrochemical reactions and so some of the details of this catalyzed coreaction were examined. The result is a fortunate enhancement of detection limit so that As(v) at 40 ppb can be measured.

Arsenic is ubiquitous whether it is naturally occurring or produced by humans. It is found at sites on the National Priority List and at sites operated by DOE, where it is the second most commonly found contaminant. More wastes containing arsenic will be produced due to the lowering of the Maximum Contaminant Level (MCL) for arsenic in drinking water which will result in more treatment facilities for arsenic removal that will generate residuals. Furthermore, arsenic can be released from such wastes under the reduced conditions that are found in landfills. Pyrite (FeS2) is believed to be a compound that has a high affinity for arsenic and is stable under anoxic conditions. The first task of this research was to develop a method for making pyrite crystals of defined size with minimal reaction time and at high yield. Effects on the synthesis of pyrite particles of pH, the ratio of Fe/S, temperature and reaction time were investigated in batch reactor systems. Pyrite was synthesized within 24 hours at pH values ranging from pH 3.6 through pH 5.6, and at a ratio of Fe/S of 0.5. X-ray diffraction and scanning electron microscopy were used to size and characterize the pyrite particles. Experimental and analytical procedures developed for this work, included a hydride generation atomic absorption spectrometry method for measuring arsenic species (As(III), As(V)). The synthesized pyrite was applied to remove arsenic and its maximum capacity for arsenic removal was measured in batch adsorption experiments to be 3.23 μmol/g for As(III) and 113 μmol/g for As(V). Information obtained on the characteristics of chemical species before and after the reaction with arsenic showed that iron and sulfur were oxidized. Last, how strongly arsenic was bound to pyrite was investigated and it was determined that release of arsenic from As(III)-pyrite is not affected by pH, but release from As(V)-pyrite is affected by pH with minimum release in the range pH 5 to pH 8.

The purposes of this study are to evaluate and elucidate distribution patterns, speciation and pollution status of As and Hg in coastal sediments. The study focuses on coastal zones off southwestern Taiwan including the Kaoping River estuary, the Kaoping Canyon, Chiku and Tapong lagoons. Experimental results show that As and Hg in surface sediments from the Kaoping River estuary are mainly associated with mud (clay+silt) and TOC. They may also co-precipitate with Fe-Mn oxides/ hydroxides in sediments. Consequently, the seasonal variability of As and Hg distributions in estuarine sediments is likely attributed to the variations of particles size and TOC contents. Distributions of As in surface sediments from the Kaoping Canyon are also related closely to mud, Fe-Mn oxides and TOC contents. The spatial variation of surface enrichment of As, however, is insignificant along the Kaoping Canyon. Concentrations of Hg in surface sediments are elevated around the river mouth and decrease seaward in the Kaoping Canyon. According to As and Hg distributions and accumulation rates in the Kaoping Canyon, pollution appears to increase significantly around 1970 corresponding to the period of economic boom in Taiwan. With the exception of locations near the Chiku River and Daliao Creek, spatial distributions of As and Hg are largely determined by particle size, organic and Fe-Mn contents. In the Tapong Bay, concentrations and enrichments of As and Hg are generally higher in the inner bay than in the outer bay, primarily affected by distributions of particle size, organic and Fe-Mn contents. The enrichment of Hg in the inner bay appears to be enhanced by waste-water discharge, TOC accumulation and sulphide formation. The magnitudes of EF are larger in the Tapong Bay than in the Chiku Lagoon and the Kaoping River estuary for both As and Hg, indicating a higher pollution status in the Tapong Bay than in other areas. Sequential extractions separate As and Hg into five fractions that can be roughly divided into mobile phase and non-mobile phase (residual fraction). The sum of mobile-like fractions is significantly correlated with the content extracted with 0.1M HCl. Arsenic and mercury speciation of sediments are quite similar in the Kaoping River estuary, the Chiku Lagoon and Tapong Bay. Both As and Hg are mostly concentrated in the residual fraction, and secondly located in Fe-Mn oxides for As, and in organic matter for Hg. Arsenic and mercury speciation in sediments are apparently not controlled by the variability of salinity in the estuary.

a b s t r a c t The effects of arsenic stress on the production of low molecular weight thiols (LMWT), glutathione S-transferase activity (GST) and sulfur metabolism of mesquite plant (Prosopis sp.) were examined in hydroponic culture at different arsenic [As(III) and (V)] concentrations. The production of LMWT was dependent on As speciation and concentration in the growth medium. The roots of As(III) treated plants produced significantly higher LMWT levels than As(V) treated roots at the same concentration of As applied. In leaves, the thiols content increased with increasing As(III) and (V) concentrations in the medium. Hypersensitivity of the plant to high As concentrations was observed by a significant decrease of LMWT produced in the roots at 50 mg/L treatment in both As(III) and (V) treatments. Sulfur was translocated from roots and accumulated mainly in the shoots. In response to As-induced phytotoxicity, the plants slightly increased the sulfur content in the roots at the highest As treatment. Compared with As(V)-treated plants, As(III)-treated roots and leaves showed significantly higher GST activity. The roots of both As(III) and (V) treated plants showed an initial increase in GST at low As concentration (5 mg/L), followed by significant inhibition up to 50 mg/L. The leaves had the highest GST activity, an indication of the ability of the plant to detoxify As in the leaves than in the roots. The correlation between LMWT content, S content and GST activity may be an indication these parameters may be used as biomarkers of As stress in mesquite.

At Cameco mine sites in northern Saskatchewan, naturally occurring elements of concern (EOC) such as As, Ni, Mo, and Se are present in uranium ore bodies. Ferrihydrite (Fh) is found in tailings management facilities (TMF) and is known to sequester arsenates and arsenites. Fh is known to be metastable and undergo phase transformations to goethite (α-FeOOH) and hematite (α-Fe2O3). Reductive conditions are known to be a driving force in Fh transformation and the release of adsorbed As species from the surface. This study uses electrochemistry to control reductive potentials applied to Fh adsorbed As species. Electrochemistry was coupled with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to determine the behaviour of adsorbed arsenate and arsenite on the Fh surface. The potentials required to desorb As(III) and As(V) from the Fh surface were negative enough to cause the reduction of water, thus increasing the pH of the solution through the generation of OH-. In order to measure the extent of the pH change a miniature palladium/palladium oxide pH sensor was fabricated in order to make in-situ pH measurements during spectroelectrochemical studies. Additionally, in-situ solution potential (Eh) measurements were made during potential control. It was found that potential induced pH and Eh changes were significant enough to release arsenite from the Fh surface. Arsenate was also found to desorb from Fh during the application of reductive potentials though successive deprotonation leading to a totally deprotonated As(V) species.

No description available.