Multiple studies in the Bengal basin have shown that elevated As in groundwater coincides with reduced, relatively dark sediments of Himalayan provenance. In West Bengal state (India), As concentrations > 10 μg/L tend to occur east of the River Bhagirathi-Hoogly, the main distributary of the Ganges. Associations among sediment chemistry and mineralogy for four cores from either side of the Bhagirathi-Hoogly (cores 1 and 2 to the east, 3 and 4 to the west) in Murshidabad district were investigated. Ten sediment samples were collected from each boring at various depths to a maximum of 38 to 43 m. Sediment chemistry was investigated using sequential extraction, digestion and analysis of As, Al, Ca, Fe, and Mn on an ICP-OES and GFAAS, and by total carbon analysis on a CNS analyzer. Organic carbon content was measured gravimetrically by HCl digestion. Sediment mineralogy was investigated using thin-section petrography and a microprobe EDS. Pyroxenes and phyllosilicates appear to be the primary sources of arsenic in the study area. Additionally, core 4 sediments are mineralogically similar to cores 1 and 2 despite differences in arsenic concentrations in the groundwater. We conclude that a 65-ft (20-m) silt layer overlying the aquifer sands in core 4 acts as a local aquitard and restricts arsenic mobilization locally.

Introduction: L'Arsenic (As) est un cancérigène reconnu et est suspecté pour ses propriétés de perturbateur endocrinien. En Abitibi-Témiscamingue (A-T), plusieurs puits privés contiennent des concentrations en As inorganique (iAs) qui dépassent la concentration maximale acceptable (CMA) de 10 [mu]g/L recommandée par Santé Canada ce qui pourrait avoir des conséquences sur la santé. Objectifs: 1- Vérifier la corrélation entre le niveau de contamination des puits en As et les indicateurs de fonction thyroïdienne en circulation dans le sang; 2- Mesurer la relation entre le niveau de contamination des puits en As et la prévalence du diabète. Méthode: Une étude descriptive transversale a été effectuée chez les propriétaires de puits privés de huit municipalités de l'A-T. Pour être éligible, les personnes intéressées devaient boire ou utiliser l'eau non traitée de leur puits pour la préparation de breuvages ou la cuisson d'aliments depuis au moins un mois, être âgées de 7 ans et plus et ne pas être exposées à l'iAs au travail. La dose externe a été estimée à l'aide de la concentration d'iAs dans l'eau du puits. La dose interne a été estimée par des mesures d'As urinaire non alimentaire (somme d'AMMA, ADMA, AslIl, et AsV) corrigées pour la créatinine et d'As total dans les ongles d'orteils. Des prélèvements sanguins ont servi à l'analyse de la fonction thyroïdienne (TSH, T3L et T4L), des anticorps anti-thyroïdiens (anti-TPO et anti-TG) et de l' HbA1c. Résultats: La moyenne géométrique de la concentration d'iAs des puits à l'étude (n=153) etait de 14,2 [mu]g/L. Après exclusion des participants traités pour hypothyroïdie et contrôle des facteurs de confusion (âge, sexe, anticorps anti-thyroïdiens, sources d'As alimentaire, tabagisme et histoire familiale de troubles thyroïdiens), une analyse de régression linéaire a indiqué que l'iAs dans l'eau du puits était positivement associé à la TSH (p=0,001) et négativement associé à la T3L (p<0,001) et à la T4L (p=0,003) chez les adultes alors que seule la TSH était associée à cet indicateur d'exposition chez les enfants (p=0,004). Une analyse de régression logistique effectuée apres contrôle des facteurs de confusion (âge, sexe, sources d'As alimentaire, histoire familiale de diabète, IMC) a aussi révélé que la présence de l'un ou l'autre des indicateurs de diabète (HbA1c>6,0%, présence d'antécédent personnel de diabète, consommation d'hypoglycémiants oraux ou prise d'insuline) était associé à l'iAs dans l'eau du puits (p=0,009) et à l'As unguéal (p=0,019) chez les adultes. Un adulte diabétique avait 2,84 fois plus de chance d'être exposé à plus de 33 [mu]g/L d'iAs dans l'eau du puits qu'un non-diabétique (IC95%: L29-6,24; p=0,010). Conclusion: Cette étude supporte la possibilité que l'iAs à faible dose entraîne des effets endocriniens.

The aim of this study was to investigate the removal of cobalt from zinc sulfate solution by cementation with the help of conventional and new type of additives that were 4% Sn-zinc alloy powder and 10% Sn-zinc alloy powder, respectively. Synthetic leach solutions containing 150 g/l Zn and 75 mg/l Co were prepared and used in all of the experiments. The parameters researched with the conventional method were the amount of arsenic trioxide and the effect of copper sulfate on cementation of cobalt. While using the alloys, the parameters studied were the amounts of arsenic trioxide, copper sulfate and tin containing zinc alloy powder additions, cementation duration and temperature. The difference in the optimization of alloy additions was in the amount of addition of arsenic trioxide. The amount of 4%Sn-zinc alloy powder was tried to be optimized with the addition of arsenic trioxide whereas the optimization was tried to be done without any arsenic addition while using 10%Sn-zinc alloy. The XRD and SEM studies of the cementates were also performed. The obtained results indicated that tin containing alloys were much better than pure zinc. With the additions of 4 g/l 4%Sn-Zn alloy dust, 1.2 g/l CuSO4.5H2O, 0.12 g/l As2O3 and in 2 hours of cementation duration at 85-90oC, the maximum amount of cobalt cementation efficiency was achieved. The experiments indicated that cobalt in the solution could be reduced to about 2 mg/l by using 10%Sn-zinc alloy powder with an initial Sn/Co weight ratio of 13.25:1 without the addition of arsenic trioxide at 85oC in 2 hours of cementation duration.

Naturally occurring arsenic (As) in Holocene aquifers in Bangladesh have undermined a long success of supplying the population with safe drinking water. Arsenic is mobilised in reducing environments through reductive dissolution of Fe(III)-oxyhydroxides. Several studies have shown that many of the tested mitigation options have not been well accepted by the people. Instead, local drillers target presumed safe groundwater on the basis of the colour of the sediments. The overall objective of the study has thus been focussed on assessing the potential for local drillers to target As safe groundwater. The specific objectives have been to validate the correlation between aquifer sediment colours and groundwater chemical composition, characterize aqueous and solid phase geochemistry and dynamics of As mobility and to assess the risk for cross-contamination of As between aquifers in Daudkandi and Matlab Upazilas in SE-Bangladesh. In Matlab, drillings to a depth of 60 m revealed two distinct hydrostratigraphic units, a strongly reducing aquifer unit with black to grey sediments overlies a patchy sequence of weathered and oxidised white, yellowish-grey to reddish-brown sediment. The aquifers are separated by an impervious clay unit. The reducing aquifer is characterized by high concentrations of dissolved As, DOC, Fe and PO43--tot. On the other hand, the off-white and red sediments contain relatively higher concentrations of Mn and SO42- and low As. Groundwater chemistry correlates well with the colours of the aquifer sediments. Geochemical investigations indicate that secondary mineral phases control dissolved concentrations of Mn, Fe and PO43--tot. Dissolved As is influenced by the amount of Hfo, pH and PO43--tot as a competing ion. Laboratory studies suggest that oxidised sediments have a higher capacity to absorb As. Monitored hydraulic heads and groundwater modelling illustrate a complex aquifer system with three aquifers to a depth of 250 m. Groundwater modelling illustrate two groundwater flowsystems: i) a deeper regional predominantly horizontal flow system, and ii) a number of shallow local flow systems. It was confirmed that groundwater irrigation, locally, affects the hydraulic heads at deeper depths. The aquifer system is however fully recharged during the monsoon. Groundwater abstraction for drinking water purposes in rural areas poses little threat for cross-contamination. Installing irrigation- or high capacity drinking water supply wells at deeper depths is however strongly discouraged and assessing sustainability of targeted low-As aquifers remain a main concern. The knowledge gained here can be used for developing guidelines for installing safe wells at similar environments in other areas of Bangladesh. / QC 20111227

"Three sampling campaigns were conducted in the Ballarat, Creswick and Maldon areas. The sampling area is part of the Golden Triangle region where significant gold-mining activities took place from the 1850s to the present day. [...] Locations were chosen to evaluate arsenic distribution in soils, surface waters and plants in different environments. Easy access to sampling locations allowed detailed scientific sampling, especially in the seasonality study. The different range of environments such as agricultural, state forest, mining, urban and rural provided an opportunity to compare the concentrations of arsenic and other elements in the study area. The study of the three selected areas combined provided further understanding of possible exposure and pathways through which arsenic can get into the food chain. "The objective of the study is to measure levels of heavy metals/metalloids in soils, water and plants in various environments, identify whether the heavy metals/metalloids are mobile and bioavailable and understand the importance of clays and oxide complexes in the fixation of metals." / Doctor of Philosophy (PhD)

"Three sampling campaigns were conducted in the Ballarat, Creswick and Maldon areas. The sampling area is part of the Golden Triangle region where significant gold-mining activities took place from the 1850s to the present day. [...] Locations were chosen to evaluate arsenic distribution in soils, surface waters and plants in different environments. Easy access to sampling locations allowed detailed scientific sampling, especially in the seasonality study. The different range of environments such as agricultural, state forest, mining, urban and rural provided an opportunity to compare the concentrations of arsenic and other elements in the study area. The study of the three selected areas combined provided further understanding of possible exposure and pathways through which arsenic can get into the food chain. "The objective of the study is to measure levels of heavy metals/metalloids in soils, water and plants in various environments, identify whether the heavy metals/metalloids are mobile and bioavailable and understand the importance of clays and oxide complexes in the fixation of metals." / Doctor of Philosophy (PhD)

In this thesis, a combination of laboratory experimentation under well defined conditions coupled with a kinetic modelling approach is used to verify the existence and respective kinetic rates of previously unconfirmed or postulated mechanisms that drive and limit dark Fenton (Fe(II)/H2O2) - mediated As(III) oxidation at pH 3 and 8 and dark Cu(II) - H2O2 - mediated As(III) oxidation at pH 8. Dark Fenton - mediated oxidation of As(III) at pH 3 is first examined and the effects of the variation in the concentration of reactants (As(III), Fe(II) and H2O2), oxygen, phosphate and organics (2 - propanol, formate, and citrate) are reported and analysed. The kinetic models developed for these systems show high applicability to full scale water treatment application and key mechanistic findings include the significance of the cycling of Fe(II) / Fe(III) via HO2 ???/O2 ??????, the effects of As(IV) termination reactions in the absence of oxygen and the retarding effects of phosphate due to the postulated formation of a Fe(III) - phosphate complex (at a derived rate constant of 2.2 x 106 M-1s-1, that also appears to have negligible kinetic activity in terms of reduction to Fe(II) by HO2 ???/O2 ??????). The work also demonstrates the significance of the free radical by products of formate and citrate oxidation by ???OH (HCOO???/CO2 ?????? and 3HGA???2???). The examination of the dark Cu(II) - H2O2 - mediated oxidation of As(III) at pH 8 with variation in the concentration of reactants (As(III), Fe(II) and H2O2), carbonate and organics (2 - propanol, formate and citrate) demonstrated for the first time the high applicability of this system to the pre - oxidation of As(III) in water treatment and mechanistically that ???OH and CO3 ?????? are the dominant As(III) oxidants in this system. The As(III) oxidant CO3 ??????, is suggested to be generated by the interaction of ???OH and O2 ?????? with the carbonate matrix, at the respective rate constants of 4.9 x 107 M-1s-1 and 5.5 x 106 M-1s-1. Examination of the dark Fenton - mediated oxidation of As(III) at pH 8 and the effects of variation in the concentration of reactants (As(III), Fe(II) and H2O2), carbonate, organics (2 - propanol, formate and citrate) and Cu(II) demonstrates the varied potential mechanistic pathways in relation to the generation of As(III) oxidants from the Fenton reaction, Fe(II) + H2O2 such as Fe(IV) and CO3 ?????? and the previously dismissed ???OH, due to the presence of Fe(II) - citrate complexes. This work also demonstrates and models the enhancement of As(III) oxidation in the presence of an additional transitional metal ion, Cu(II).

Arsenic (As) in groundwater systems is a problem in many parts of the world owing to ever-increasing extraction of groundwater resources to meet the needs of growing populations. Surprisingly, the occurrence of elevated As concentrations in coastal sandy aquifers has only recently been published as a result of this research. Sandy aquifers are commonly used as a clean and reliable source of water for domestic, agricultural and industrial needs due to their high recharge rates and the filtering capacity of sands. Water quality monitoring in Australian sandy aquifers is usually limited to a small suite of major elements and salinity measurements to determine the quality of groundwater and to identify any potential problems from seawater intrusion as a result of over extraction. Minor and trace elements, particularly toxic elements, have largely been ignored in regular monitoring programs. Prompted by an emerging pattern of human health problems in a community reliant on groundwater, hydrogeochemical investigations of the Stuarts Point coastal sand aquifer, on the North Coast of New South Wales, Australia, identified elevated As concentrations of up to 337 ????g/L in the catchment's Pleistocene barrier sands. These concentrations are well in excess of the World Health Organisation and the Australian National Health and Medical Research Council water quality criteria of 10 and 7 ????g/L respectively. From research into the Stuarts Point geology, geochemistry, geomorphology, hydrogeology and hydrogeochemistry, and with the assistance of environmental isotopes, the spatial distribution, occurrence and mobilisation processes of As were determined. The presence and distribution of elevated As concentrations in the regional coastal aquifer system are sporadic and involve a series of complex hydrogeochemical processes. No single hydrogeochemical process can describe the release of As from solid phase to groundwater system on the regional scale. Processes of competitive exchange with PO43- and HCO3-, reductive dissolution of Fe oxyhydroxides and arsenical pyrite oxidation, though not forming dominant correlations, are still evident and influence As chemistry at this scale. Detailed investigations of the hydrogeochemistry on the vertical scale have identified two main processes as causing As to be released and mobilised. The first process is associated with the oxidation of arsenical pyrite in Acid Sulphate Soils and metal hydrolysis reactions which mobilise As in the acidic environment. In the absence of dissolved oxygen (DO), NO3- acts as the oxyanion facilitating arsenical pyrite oxidation and releasing As into solution. The second process that mobilises As from the sediments is the liberation of As from metal-oxyhydroxides in the carbon-rich environment, where HCO3- originates from the dissolution of shell material in the Pleistocene barrier sands. The marine influenced depositional history and geomorphology of the aquifer provide opportunities for As to become incorporated into the aquifers matrix in a variety of mineral forms, which is an occurrence not considered to be unique to the Stuarts Point catchment. The findings presented here are amongst the first detailed studies of naturally occurring As in an Australian groundwater system as well as in the Pleistocene coastal sand aquifer environment. The understanding of As accumulation and mobilisation identified as a result of this research emphasises the need for potential As occurrences in similar groundwater systems in other coastal environments in Australia, and globally, to be considered.

Doctor of Philosophy(PhD) / Soil contamination with heavy metal(loid)s is a major environmental problem that requires effective and affordable remediation technologies. The utilisation of plants to remediate heavy metal(loid)s contaminated soils has attracted considerable interest as a low cost green remediation technology. The process is referred to as phytoremediation, and this versatile technology utilises plants to phytostabilise and/or phytoextract heavy metal(loid)s from contaminated soils, thereby effectively minimising their threat to ecosystem, human and animal health. Plants that can accumulate exceptionally high concentrations of heavy metal(loid)s into above-ground biomass are referred to as hyperaccumulators, and may be exploited in phytoremediation, geobotanical prospecting and/or phytomining of low-grade ore bodies. Despite the apparent tangible benefits of utilising phytoremediation techniques, a greater understanding is required to comprehend the ecophysiological aspects of species suitable for phytoremediation purposes. A screening study was instigated to assess phytoremediation potential of several fern species for soils contaminated with cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn). Hyperaccumulation was not observed in any of the studied species, and in general, species excluded heavy metal uptake by restricting their translocation into aboveground biomass. Nephrolepis cordifolia and Hypolepis muelleri were identified as possible candidates in phytostabilisation of Cu-, Pb-, Ni- or Zn-contaminated soils and Dennstaedtia davallioides appeared favourable for use in phytostabilisation of Cu- and Zn-contaminated soils. Conversely, Blechnum nudum, B. cartilagineum, Doodia aspera and Calochlaena dubia were least tolerant to most heavy metals and were classified as being least suitable for phytoremediation purposes Ensuing studies addressed the physiology of arsenic (As) hyperaccumulation in a lesser known hyperaccumulator, Pityrogramma calomelanos var. austroamericana. The phytoremediation potential of this species was compared with that of the well known As hyperaccumulator Pteris vittata. Arsenic concentration of 3,008 mg kg–1 dry weight (DW) occurred in P. calomelanos var. austroamericana fronds when exposed to 50 mg kg–1 As without visual symptoms of phytotoxicities. Conversely, P. vittata was able to hyperaccumulate 10,753 mg As kg–1 DW when exposed to 100 mg kg–1 As without the onset of phytotoxicities. In P. calomelanos var. austroamericana, As was readily translocated to fronds with concentrations 75 times greater in fronds than in roots. This species has the potential for use in phytoremediation of soils with As levels up to 50 mg kg–1. Localisation and spatial distribution of As in P. calomelanos var. austroamericana pinnule and stipe tissues was investigated using micro-proton induced X-ray emission spectrometry (µ-PIXE). Freeze-drying and freeze-substitution protocols (using tetrahydrofuran [THF] as a freeze-substitution medium) were compared to ascertain their usefulness in tissue preservation. Micro-PIXE results indicated that pinnule sections prepared by freeze-drying adequately preserved the spatial elemental distribution and tissue structure of pinnule samples. In pinnules, µ-PIXE results indicated higher As concentration than in stipe tissues, with concentrations of 3,700 and 1,600 mg As kg–1 DW, respectively. In pinnules, a clear pattern of cellular localisation was not resolved whereas vascular bundles in stipe tissues contained the highest As concentration (2,000 mg As kg–1 DW). Building on these µ-PIXE results, the chemical speciation of As in P. calomelanos var. austroamericana was determined using micro-focused X-ray fluorescence (µ-XRF) spectroscopy in conjunction with micro-focused X-ray absorption near edge structure (µ-XANES) spectroscopy. The results suggested that arsenate (AsV) absorbed by roots was reduced to arsenite (AsIII) in roots prior to transport through vascular tissues as AsV and AsIII. In pinnules, AsIII was the predominant species, presumably as aqueous-oxygen coordinated compounds. Linear least-squares combination fits of µ-XANES spectra showed AsIII as the predominant component in all tissues sampled. The results also revealed that sulphur containing thiolates may, in part sequester accumulated As. The final aspect of this thesis examined several ecophysiological strategies of Ni hyperaccumulation in Hybanthus floribundus subsp. floribundus, a native Australian perennial shrub species and promising candidate in phytoremediation of Ni-contaminated soils. Micro-PIXE analysis revealed that cellular structure in leaf tissues prepared by freeze-drying was adequately preserved as compared to THF freeze-substituted tissues. Elemental distribution maps of leaves showed that Ni was preferentially localised in the adaxial epidermal tissues and leaf margin, with concentration of 10,000 kg–1 DW in both regions. Nickel concentrations in stem tissues obtained by µ-PIXE analysis were lower than in the leaf tissues (1,800 mg kg–1 vs. 7,800 mg kg–1 DW, respectively), and there was no clear pattern of compartmentalisation across different anatomical regions. It is possible that storage of accumulated Ni in epidermal tissues may provide Ni tolerance to this species, and may further act as a deterrent against herbivory and pathogenic attack. In H. floribundus subsp. floribundus seeds, µ-PIXE analysis did not resolve a clear pattern of Ni compartmentalisation and suggests that Ni was able to move apoplastically within the seed tissues. The role of organic acids and free amino acids (low molecular weight ligands [LMW]) in Ni detoxification in H. floribundus subsp. floribundus were quantified using high performance liquid chromatography (HPLC) and ultra performance liquid chromatography (UPLC). Nickel accumulation stimulated a significant increase in citric acid concentration in leaf extracts, and based on the molar ratios of Ni to citric acid (1.3:1–1.7:1), citric acid was sufficient to account for approximately 50% of the accumulated Ni. Glutamine, alanine and aspartic acid concentrations were also stimulated in response to Ni hyperaccumulation and accounted for up to 75% of the total free amino acid concentration in leaf extracts. Together, these LMW ligands may complex with accumulated Ni and contribute to its detoxification and storage in this hyperaccumulator species. Lastly, the hypothesis that hyperaccumulation of Ni in certain plants may act as an osmoticum under water stress (drought) was tested in context of H. floribundus subsp. floribundus. A 38% decline in water potential and a 68% decline in osmotic potential occurred between water stressed and unstressed plants, however, this was not matched by an increase in accumulated Ni. The results suggested that Ni was unlikely to play a role in osmotic adjustment in this species. Drought stressed plants exhibited a low water use efficiency which might be a conservative ecophysiological strategy enabling survival of this species in competitive water-limited environments.

Thesis (Ph. D.)--University of Texas at El Paso, 2007. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.