Arsenic contamination of groundwater has been reported in over 20 countries worldwide where tens of millions of people are being exposed to excessive levels of arsenic in their drinking water, especially in countries of the Asian region, Bangladesh in particular. This study focusses on analytical techniques currently used for the estimation and speciation of arsenic in aqueous phase (soil and water) and in plant tissues; the uptake of arsenic by two commonly used vegetable crops (amaranth and silverbeet) using solution culture and pot culture studies; speciation-toxicity relationship of arsenic to plants; the nature of arsenic species in plant tissue and Bangladesh groundwater samples; and the effect of iron (Fe) on arsenic (As) uptake by plants and animals. / Thesis (PhD)--University of South Australia, 2006.

Arsenic contamination of groundwater has been reported in over 20 countries worldwide where tens of millions of people are being exposed to excessive levels of arsenic in their drinking water, especially in countries of the Asian region, Bangladesh in particular. This study focusses on analytical techniques currently used for the estimation and speciation of arsenic in aqueous phase (soil and water) and in plant tissues; the uptake of arsenic by two commonly used vegetable crops (amaranth and silverbeet) using solution culture and pot culture studies; speciation-toxicity relationship of arsenic to plants; the nature of arsenic species in plant tissue and Bangladesh groundwater samples; and the effect of iron (Fe) on arsenic (As) uptake by plants and animals. / Thesis (PhD)--University of South Australia, 2006.

Sulfide minerals have been suggested to play an important role in regulating dissolved metal concentrations in anoxic environments. Pyrite is the most common sulfide mineral and it has shown an affinity for arsenic, but little is known about the arsenic retention mechanisms of pyrite. In this study, interactions of arsenic with pyrite were investigated in an anoxic environment to understand geochemical cycling of arsenic better and to predict arsenic fate and transport in the environment better. A procedure using microwaves was studied to develop a fast and reliable method for synthesizing pyrite. Arsenic-pyrite interactions were investigated using macroscopic (solution phase experiments) and microscopic (X-ray photoelectron spectroscopic investigation) approaches. Pyrite was successfully synthesized within a few minutes via reaction of ferric iron and hydrogen sulfide under the influence of irradiation by a conventional microwave oven. The SEM-EDX study revealed that the nucleation and growth of pyrite occurred on the surface of elemental sulfur, where polysulfides are available. Compared to conventional heating, microwave energy results in rapid (< 1 minute) formation of smaller particulates of pyrite. Higher levels of microwave power can form pyrite even faster, but faster reaction can lead to the formation of pyrite with defects. Arsenic removal by pyrite was strongly dependent on pH and arsenic species. Both arsenite (As(III)) and arsenate (As(V)) had a strong affinity for the pyrite surface under acidic conditions, but As(III) was removed more effectively than As(V). Under acidic conditions, arsenic removal continued to occur almost linearly with time until complete removal was achieved. However, under neutral to alkaline conditions, fast removal was followed by slow removal and complete removal was not achieved in our experimental conditions. A BET isotherm equation provided the best fit to arsenic removal data, suggesting that surface precipitation occurred at high arsenic/pyrite ratio. The addition of competing ions did not substantially affect the ultimate distribution of arsenic between the pyrite surface and the solution, but changing pH affected arsenic stability on pyrite. X-ray photoelectron spectroscopy revealed that under acidic conditions, arsenic was removed and formed solid phases similar to As2S3 and As4S4 by reaction with pyrite. However, under neutral to alkaline conditions, arsenic was removed and formed As(III)-O and As(V)-O surface complexes, as well as As2S3/As4S4-like precipitates. As pH increases, the amount of arsenic that formed As2S3/As4S4-like precipitates decreased, while the amount that formed As(III)-O and As(V)-O surface complexes increased. Under alkaline conditions, a FeAsS-like phase was also detected.

Given that the mobility, bioavailability, and toxicity of arsenate in natural systems is often controlled by the strong binding capacity of iron oxyhydroxides, the objective of this study was to document the interactions of Dowex M4195 Fe3+-substituted chelating resins (a potential fieldbased tool for the quantification of potential arsenate bioavailability) and arsenic-bearing ferrihydrite (AFH) as a function of suspension pH, suspension concentration, and background electrolyte concentration. In 0.5 g AFH/L (0.001 M NaNO3) suspensions, arsenate sorption to the resins was proportional to the degree of acidification of the AFH suspensions by the resins. H+-enhanced dissolution of ferrihydrite artificially increased the arsenate in solution, causing a consistent overestimation of potential arsenate bioavailability. Resin-induced acidification was decreased with increasing suspension concentration. Arsenate sorption to the resins in 0.5 g/L suspensions at pH 8 decreased with increasing NaNO3 concentrations, reflecting the decreasing activity of arsenate under these conditions. The results of this study indicate that the high buffer capacity of natural soils would prevent acidification as a result of resin introduction. Thus, Dowex M4195 Fe3+-substituted chelating resins should provide a reasonable assessment of potential arsenate bioavailability from poorly-crystalline iron oxide minerals. Possibly more importantly, Dowex M4195 Fe3+-substituted chelating resins appear to be a new choice of passive equilibrium sampling device that should work well for the determination of bioavailable arsenate concentrations in the field.

Reproduction de : Thèse de doctorat : Toxicologie : Metz : 1978. / Titre provenant de l'écran-titre. Notes bibliographiques. Index.

Thesis (Ph. D.)--University of Queensland, 2003. / Includes bibliographical references.

Abstract The status and the distribution of arsenic in soils from a disused cattle dip were determined. Elevated total arsenic levels (1,033–1,369 mg/L) were detected in the soils. Significant difference (p\0.05) between the values for the soils obtained from the contaminated sites and control site (0.15 mg/L) was observed. The level of total arsenic decreased with increase in depth. The peak total arsenic (1,369 mg/L) was obtained at 0 cm depth, indicating the abundance of arsenic at the surface despite the fact that the dip has been out of use for a long time. The total arsenic recorded for different depths were significantly higher than the trigger value of 40 mg/kg. The distribution of arsenic in the different phases showed that arsenic was mostly bound to the residual fractions (52%) and Fe and Al hydroxides (21%). The distribution of arsenic in the order phases was in the following order: exchangeable (14%), carbonates (10%) and soluble (3%).

Antimony is a potential human and ecosystem health risk, yet large gaps in the existing knowledge of the geochemical behaviour of Sb persist. At the Giant mine, an abandoned gold mine about to undergo remediation, Sb is elevated in mine waste and in downstream pond and stream sediments that have been impacted by mine waste. Gold at the Giant Mine, Yellowknife NT, is refractory, hosted in arsenopyrite (FeAsS) and pyrite (FeS2), and associated with stibnite (Sb2S3) and Sb-sulfosalts. The gold was liberated by roasting the ore which produced two arsenic (As) and antimony (Sb)-rich waste streams: calcine and electrostatic precipitator (ESP) residue. The roaster-derived As and Sb host phases, maghemite and hematite, are found in sediment, and are undergoing post-depositional transformations. Bulk and micro- X-ray Absorption Near Edge Spectroscopy (XANES) methods, and synchrotron-based micro-X-ray fluorescence (μXRF) and micro-X-ray diffraction (μXRD), were employed to characterize the Sb-host phases and determine the solid-phase speciation of Sb in mine waste and sediment. Antimony in mine waste is largely associated with roaster-derived maghemite and is hosted as Sb(III) and Sb(V). The bulk and μXANES analyses indicate a more prominent Sb(III) composition in the ESP residue, compared to the calcine. In the surficial and deeper sediment Sb(III) and Sb(V) bound to oxygen are present, as well as Sb(III) bound to sulfur in the deeper sediment. The presence of the Sb(III) bound to sulfur phase in the deeper sediment implies that Sb associated with the roaster oxides is destabilized, but subsequently precipitates as, or adsorbs onto, a sulfide. Furthermore, the preferential attenuation of the Sb(III) species likely accounts for the dominance of Sb(V) in pore-water at all three sites, and at all depths. Co-existing with the sulfur-bound Sb phases in the deeper, relatively reducing sediment, is a compositionally significant, and finely disseminated Sb(V) bound to oxygen phase. Antimony and As are often assumed to exhibit similar geochemical behaviour. This study offered an opportunity to compare the mobility of As and Sb since both are elevated in concentration in the environment and in mine waste. Arsenic and Sb exhibit similar geochemical behaviour in the upper 2cm, but the higher affinity of As for sorption sites results in dissimilar distribution in pore-water. Both elements undergo post-depositional reduction resulting in an increase in the mobility of As, and attenuation of Sb. Aquatic horsetails (Equisetum fluviatile) present in Baker Creek significantly reduces the mobility of both elements. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2009-02-08 16:57:48.711

Safe water options for five arsenic-affected villages (Sarupie, Manikganj; Daniapara, Shirajdekhan; Babutepara, Muradnagar; Iruaien, Laksham; Rahulllabad, Nabinagar) in central Bangladesh were studied in order to assist the local people and to obtain an indication of general solutions to the arsenic problem that is currently affecting ~100 million people on the Indian subcontinent. Arsenic concentrations were measured in all drinking waters believed to be safe and in a random sample of "red" (unsafe) tubewell waters. Depending on geography, history of safe water sources and availability of pond/river, the options of dugwells, deep tubewells and sand filters were recommended for core village areas, combined with sustainable output testing and a distribution system to maximise the benefits of sustainable water output. Very shallow tubewells were recommended for testing in villages where dugwells were successful. Rainwater harvesting was not recommended, due to expense, small storage capacity and summer dry periods. Two dugwells of optimised design were constructed in Iruaien and Daniapara, each serving 50-100 families. The knowledge gained in the villages was incorporated into the first draft of a "Safe Water Book" for dissemination of honest and accurate information about solutions to the arsenic problem. An air/iron treatment system was developed for removal of arsenic from tubewell water in locations where water treatment is the only option available. The system is based on the Bangladeshi "three kalshi" method, but optimised for efficient contact of water with air and iron. It can be constructed like a sand filter, and requires no chemical input, except for clean scrap iron. Spent scrap iron containing arsenic can be incorporated into concrete for safe disposal. A model air/iron system was constructed and run for two years to demonstrate the long-term viability of the device. A colorimetric method, using silver diethyldithiocarbamate, was developed for determination of arsenic in the villages of Bangladesh. The equipment was adapted for rugged field use, and performed successfully without electricity or running water in improvised laboratory space in villages, providing linear calibrations 0-500 ??g/L and a 2σ limit of detection of 5 ??g/L. The appropriate technologies that should be developed or optimised for the arsenic affected region are described and preliminary suggestions are given about means by which self-propagating solutions might be developed in villages to solve the arsenic problem.

Safe water options for five arsenic-affected villages (Sarupie, Manikganj; Daniapara, Shirajdekhan; Babutepara, Muradnagar; Iruaien, Laksham; Rahulllabad, Nabinagar) in central Bangladesh were studied in order to assist the local people and to obtain an indication of general solutions to the arsenic problem that is currently affecting ~100 million people on the Indian subcontinent. Arsenic concentrations were measured in all drinking waters believed to be safe and in a random sample of "red" (unsafe) tubewell waters. Depending on geography, history of safe water sources and availability of pond/river, the options of dugwells, deep tubewells and sand filters were recommended for core village areas, combined with sustainable output testing and a distribution system to maximise the benefits of sustainable water output. Very shallow tubewells were recommended for testing in villages where dugwells were successful. Rainwater harvesting was not recommended, due to expense, small storage capacity and summer dry periods. Two dugwells of optimised design were constructed in Iruaien and Daniapara, each serving 50-100 families. The knowledge gained in the villages was incorporated into the first draft of a "Safe Water Book" for dissemination of honest and accurate information about solutions to the arsenic problem. An air/iron treatment system was developed for removal of arsenic from tubewell water in locations where water treatment is the only option available. The system is based on the Bangladeshi "three kalshi" method, but optimised for efficient contact of water with air and iron. It can be constructed like a sand filter, and requires no chemical input, except for clean scrap iron. Spent scrap iron containing arsenic can be incorporated into concrete for safe disposal. A model air/iron system was constructed and run for two years to demonstrate the long-term viability of the device. A colorimetric method, using silver diethyldithiocarbamate, was developed for determination of arsenic in the villages of Bangladesh. The equipment was adapted for rugged field use, and performed successfully without electricity or running water in improvised laboratory space in villages, providing linear calibrations 0-500 ??g/L and a 2σ limit of detection of 5 ??g/L. The appropriate technologies that should be developed or optimised for the arsenic affected region are described and preliminary suggestions are given about means by which self-propagating solutions might be developed in villages to solve the arsenic problem.