Thesis (M.S. - Hydrology and Water Resources) - University of Arizona. / Includes bibliographical references (leaves 230-

This dissertation combines field data, laboratory experiments, and mathematic models to (1) predict the probability of groundwater arsenic (As) contamination caused by geogenic sources and processes in shallow aquifers of the Mississippi Delta in southern Louisiana, (2) study the role microbes play in controlling As mobilization from sediments to groundwaters, and (3) simulate As mobilization and transport caused by changing redox conditions and groundwater geochemistry along a flow path within the southeastern Chicot aquifer in southern Louisiana. A model based on surface hydrology, soil properties, geology, and sedimentary deposition environments predicts that the Holocene shallow aquifers in southern Louisiana are at high risk of As contamination. Sediment incubation and pore-water chemistry suggest that microbes play a key role in mobilizing As from sediments by reductive dissolution of As-bearing Fe(III) oxides/oxyhydroxides. Finally, groundwater samples were collected along a 10 km flow path in the southeastern Chicot aquifer to determine groundwater geochemical parameters and to simulate reactive transport of Fe and As species along the studied flow path. The model well captures the general trends of Fe(II) and As(III) concentrations along the studied flow path and the close correspondence between Fe(II) and As(III) of the both measured and model predicted As(III) and Fe(II) concentrations support the hypothesis that microbially mediated reductive dissolution of As-bearing Fe(III) oxides/oxyhydroxides is the primary mechanism causing As mobilization from sediments to the shallow reducing groundwaters of the Mississippi Delta in southern Louisiana. / 1 / NINGFANG YANG

Dissertation (Ph.D.)--Auburn University, 2007. / Abstract. Vita. The research presented herein has resulted in the following publications: Radu, Tanja; Yang, Jae K.; Hilliard Jeremy H.; Barnett, Mark O.; "Transport of As (III) and As (V) in experimental subsurface systems", ACS Symposium Series 915, Advances in Arsenic Research, 2005, 91-103 Radu, Tanja; Subacz, Jonathan L.; Jonathan L.; Phillippi, John M.; Barnett, Mark O. "Effects of dissolved carbonate on arsenic adsorption and mobility" Environmental Science and Technology, 2005, 39(20), 7875-7882 Radu, Tanja; Kumar, Anjani; Clement, T. Prabhakar ; Jeppu, Gautham; Barnett, Mark O.; "Development of scalable model for predicting arsenic oxidation and adsorption at pyrolusite surfaces" Journal of Contaminant Hydrology, 2007, in press Includes bibliographic references (p.106-115).

Thesis (M.S.)--University of Nevada, Reno, 2007. / "December, 2007." Includes bibliographical references (leaves 97-100). Online version available on the World Wide Web.

The contamination of groundwater by naturally occurring arsenic (As) in South and South East Asia has resulted in the exposure of an estimated 100 million people to hazardously high concentrations of this known carcinogen. Whilst the biogeochemical processes and mechanisms responsible for releasing As to groundwater are now understood, the fundamental controls on these processes have yet to be resolved. In particular, the role of different sources of organic matter (OM) in controlling the rate and extent of As release and how the contributions of these different sources may be influenced by groundwater abstraction practices, remains poorly constrained. Indeed, it is the absence of such key information which currently limits our capability to accurately predict both where and when As will be released in to the groundwaters of this region. Elucidation of the controls of these processes is therefore of vital importance for aiding policy makers and those responsible for mitigating the effects of the current catastrophe in providing a sustainable source of As free drinking water to millions of people in the countries impacted.We conducted investigations at two known As hotspots in West Bengal and Cambodia to assess the impact of groundwater abstraction practices on the composition of dissolved organic carbon (DOC) and As release. The radiocarbon age of DOC at both sites requires a contribution of young surface or near surface derived OM as well as contributions from older, sedimentary sourced OM. Mixing profiles at the Cambodian study site suggest this subsurface OM end member to have an age of between 1000 and 6000 years. A clear association is observed between high As concentrations in shallow groundwaters containing young DOC, with lower concentrations of As being associated with older DOC in deeper groundwater. This provides the first direct confirmation that younger, more labile sources of OM are able to support more extensive As release in these aquifers. Perhaps more importantly, it is shown that modern surface derived OM can be drawn into As contaminated groundwaters. Comparison of the residence times of groundwaters suggests that the extent of ground-surface water interaction is more extensive and extends to greater depths in aquifers that have been subjected to massive groundwater abstraction. Indeed, it is suggested thatgroundwater abstraction practices may be responsible for driving the downward transport of As contaminated shallow groundwater into deeper groundwater, and may potentially be driving changes in the composition of organic carbon within the groundwater. This could give rise to a more reactive, bioavailable organic carbon pool which has the potential to further influence As mobility in these groundwaters. The potential for secular changes in the groundwater As hazard in these regions must therefore consider the impact that changes in the DOC composition may have on the biogeochemical evolution of these aquifers.

Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 104-113).

Arsenic contamination of circum-Himalayan groundwater is leading to one of the greatest humanitarian disasters of modern times, poisoning at least 70 million people who are mostly poor and rural. The groundwater is hosted in Holocene aquifers consisting of Himalayan sediments deposited by the great Asian rivers in deltaic environments. Arsenic is released when organic material (OM) reacts with the iron-oxide minerals co-deposited in the sediments onto which arsenic is adsorbed. The source of OM is one of the most important questions facing researchers and policy makers. There are generally accepted to be three potential sources of OM: 1) sedimentary bound OM (SOM) co-deposited with sediments; 2) thermally mature petroleum upwelled from reservoirs below the aquifers; 3) dissolved organic carbon (DOC) some of which might be drawn in to the aquifer through modern pumping and irrigation. In this thesis the nature of organic material in the aquifer is researched and the processes and timescales which lead to arsenic release are studied. Here evidence for a new conceptual model of arsenic release is presented. Isotopic tracing combined with a new geochemical model and organic geochemical techniques, shows that OM driving arsenic release pre-dates agriculture in the region and was from natural grasslands in the early Holocene. The geochemical model utilises strontium isotopes to correct the radiocarbon age of dissolved inorganic carbon (DIC) to find only the age and isotopic signature of DIC from oxidation of organic material. This shows that DIC from oxidation of OM was from the early Holocene and had an isotopic signature consistent with the early Holocene SOM in this region. A study of the sediments in the region built upon a geomorphological history shows that the most oxidised SOM is from early Holocene sediments. Thus both techniques separately indicate that pre-agricultural organic material drove arsenic release. This conceptual model however reveals the "arsenic sand paradox", because whilst release is from early Holocene clays, today highest concentrations of arsenic are in younger sands. Explaining this paradox is the most important next step leading on from this research.

This article presents nano composite TiO2.Fe2O3/laterite materials, which were successfully prepared by hydrometallurgical method. The materials were modified using urea as the nitrogen source. The particles size of the materials is from 20-30 nanometers. The obtained materials can not only absorb arsenic compounds but also enhance the ability of converting As (III) or As (V) into Aso, which is removed from solution. Arsenic removal efficiency of these materials is high. Using sunlight in a hydraulic retention time, about 180 minutes, the arsenic value at the inflow was about 10 mg/L but the outflow was negligible. Covering TiO2.Fe2O3 nano on laterite have brought high economical efficiency, on one hand, it saved material and on the other hand, it can be continuously operated without the centrifugal separation of the nano material. / Bài báo này giới thiệu về phương pháp điều chế vật liệu nano TiO2.Fe2O3 biến tính nitơ được phủtrên đá ong bằng phương pháp thủy luyện. Vật liệu nano thu được có kích thước 20-30 nm. Vật liệu thu được không những có khả năng hấp phụ các hợp chất của asen mà còn có khả năng khử As (III) hoặc As (V) thành Asokhi được chiếu sáng. Sử dụng ánh sáng mặt trời chiếu vào hệ thống xử lý trong thời gian 180 phút có thể loại bỏ được gần như hoàn toàn asen ra khỏi nước mặc dù hàm lượng đầu vào là 10 mg/l. Việc phủ vật liệu TiO2.Fe2O3 nano lên đá ong đã mang lại hiệu quả kinh tế cao, một mặt nó tiết kiệm được vật liệu, mặt khác, vật liệu có thể sử dụng một cách liên tục mà không cần phải tách bằng phương pháp ly tâm.