Research in selenium isotopes has been gaining interest as new contaminated sites are identified around the world. Selenium is an emerging contaminant, as it is increasingly being released through anthropogenic activities. It is an element with a very narrow range between nutrient requirement and toxic concentrations. Increased concentrations in the environment are a cause for concern. Selenium can be made less toxic in a system through reduction. Currently, investigations into fractionation caused by the reduction of Se by Fe and Fe minerals are limited. This thesis describes a batch study conducted using granular iron to treat Se(VI) in CaCO3 saturated water, under anaerobic conditions. The amount of Se(VI) in solution decreased to 14.5% of the initial concentration within three days. No quantifiable Se(IV) was found in solution. Analysis of the solid phase showed Se(IV), ferric selenite, FeSe, and Se(0) on the GI. The mass of Se0 on the GI increased over time. Iron selenide compounds became more prevalent after two days had elapsed. Effective fractionations of 4.3??? for 82/76Se and 3.0??? for 82/78Se were observed for this reaction. These effective fractionations are lower than fractionations observed in other experiments for reduction in solution. This discrepancy may be due to the reduction of Se(IV) occurring after adsorbing onto the solid phase, rather than reduction taking place only in solution.

Remediation of trace element-contaminated sites must consider both the nature of the contaminants and environmental surroundings. This thesis examined treatments for two contamination scenarios. The first study characterized chromium dynamics during the redox-sorption treatment of aqueous hexavalent chromium with the reducing agent sodium dithionite and two iron oxides. Results showed that chromium was successfully removed from solution by precipitation and sorption. The iron oxide derived from ferric chloride had a greater sorption capacity for hexavalent chromium than the oxide derived from ferrous chloride. The second study examined the phytoextraction treatment of soils contaminated with multiple trace elements. Deschampsia caespitosa plants had better early growth in the contaminated high-organic matter soil than three Brassica species. However, D. caespitosa plants did not take up sufficient amounts of trace elements during the study to be considered useful for short-term phytoextraction. These findings are applicable to the development of effective trace element remediation methods.

Plant-based remediation techniques that can address mixtures of heavy metals and organic contaminants in soil warrant investigation due to their cost effectiveness and public acceptability. The potential of phytoremediation to remediate mixtures of heavy metals and hydrocarbons in soil is presented in two papers. A hydropic screening of twenty-seven forage grasses, grown in a solution containing 100 muM Zn, 5 muM Cu and 1 muM Cd, provided six species that were exceptionally metal tolerant. These six species were examined for their growth response and root phenolic secretion at five levels of hydroponic heavy metal contamination. Phenolic secretion, an indicator of a plant's capacity to promote polycyclic aromatic hydrocarbon (PAH) degradation, increased with heavy metal contamination, however, the values were low (<30 mug/g root). Two high biomass producing, metal-tolerant grasses, Bromus riparius and Arrhenatherum elatius, were combined with M2Rhizo4, a strain of plant growth-promoting rhizobacteria. The plant-bacterial combinations were established in artificial and genuine soils contaminated with heavy metals and PAHs at a range of concentrations. In contaminant-free artificial soil, inoculation promoted B. riparius growth by 25% compared to non-inoculated plants. In artificial soil, contaminated with 495 mg/kg Zn, 263 mg/kg Cu and 23 mg/kg Cd, M2Rhizo4 promoted B. riparius growth by 22%. In chromated-copper-arsenate (CCA) and creosote contaminated soil, M2Rhizo4 inoculated A. elatius had 15% more biomass and greater survival rates than non-inoculated A. elatius. A phytoremediation system composed of metal-tolerant plants inoculated with hydrocarbon-degrading or plant growth promoting bacteria may be suitable for sites contaminated with a mixtures of hydrocarbons and heavy metals.

Heavy metals in the environment are a source of some concern because of their potential reactivity, toxicity, and mobility in the soil. Soil contamination by metals is placing human and environmental health at risk through possible contamination of food chain. / Soil washing can be used to remove metals from the soil. Chemical treatment involves the addition of extraction agents that react with the contaminant and leach it from the soil. The liquid, containing the contaminants, is separated from the soil resulting in a clean solid phase. Six chelating reagents, EDTA, Citric acid, ADA, DTPA, SCMC, and DPTA, were employed to determine the relative extraction efficiencies of the six chelating reagents for the target metals. Recycling of chelating reagent was the main interest of this study. The experiments were divided into four parts: (1) preliminary studies on the preparation and characterization of soil that included grinding, sieving, soil texture measurements, total metals content post digestion and the distribution of metals in different soil fractions as well as (2) a comparison of the extraction efficiencies of six chelating reagents toward Cu, Pb, Zn, Fe, and Mn. Additionally, the chelating reagent was liberated and recycled by treatment of the metal-complexes with disodium diethyl dithiocarbomate (DEDTC). Additionally, supercritical CO2 was used to extract metal-DEDTC complexes using various surfactants to maintain the metal-DEDTC complexes in suspension. Finally, (4) magnesium metal was evaluated as an alternative method for liberating the water-soluble chelating reagent from the complex so as to be able to recycle this reagent as well. / The different approaches were promising in terms of recycling the chelating reagents that suggests a means of optimizing the experimental conditions in future applications.

Polychlorinated biphenyls (PCBs) are toxic, stable organic contaminants that are present in air, water, soil, plants and animals all around the world. The market for PCB treatment technologies is estimated to be $300 to $600 million (Canadian dollars) for the year 2000, and will expand in future years. Existing treatment technologies to remove PCBs from soil are underutilized because they are more expensive than landfilling and incineration. This thesis presents a laboratory study of an innovative PCB remediation process that will extract PCBs from soil in-situ for subsequent destruction above ground. This remedy will remove PCBs from surficial soil without the need for excavation. Two laboratory studies were conducted on field-contaminated soil. The first experiment evaluated the effectiveness of hexane, methyl isobutyl ketone, and ethyl acetate in removing PCBs from soil. Ethyl acetate and MIBK were equally effective, removing 99% and 98% of PCBs from dry soil in 4 days, respectively. In the second experiment, soil was exposed to ethyl acetate for varying amounts of time, and some of the samples were treated a second time with fresh solvent. PCB removal increased as treatment time was increased from 10 minutes to 50, 250, and 1250 minutes, but the rate of PCB removal decreased as treatment time increased. The second 10-minute extraction removed an additional 1--10% of the remaining PCBs.

Polychlorinated biphenyls (PCBs) are a group of 209 chemical congeners that are toxic and persistent organic contaminants---they have been present in the environmental for several decades. Sites contaminated with PCBs pose serious health and safety risks to the surrounding environment due to their toxicity, persistence and bioaccumulation in creature. Polychlorinated biphenyls were commercially produced complex mixtures for a variety of applications. Before production was discontinued world-wide in 1977, several million tons of PCBs have been directly disposed to the soil. Researchers have been encouraged to develop novel techniques/approaches to detoxify PCB compounds and PCB contaminated soil. Ideally, these methods would be inexpensive, rapid, efficient and environmentally benign. / This study investigated novel approaches/techniques for PCB hydrodechlorination with noble metal catalyst in a continuous hydrogenation system, using a reactor column filled with Pd0/gamma-Al2O3 catalyst. Appreciable quantities of PCB compounds or other aromatic compounds were hydrodechlorinated and/or hydrogenated under mild conditions (90°C). The reaction efficiency was virtually complete if sufficient H2 was included in the mobile phase either by pure H2 or supercritical CO 2 combined with 5% H2. / The study also optimized conditions to wash PCBs washing condition from contaminated soil by sonication mixing and outlined an environmentally benign industrial application that combined soil washing with an at line PCBs hydrodechlorination process. The techniques/approaches developed in this study would seem to have a broad application in PCB dechlorination/detoxification and in the remediation of historically contaminated soil/sediments.

Graduation date: 1994

Thesis (M.S.)--Auburn University, 2007. / Abstract. Includes bibliographic references (ℓ. 54-62)

Thesis (M.S.)--Auburn University, 2007. / Abstract. Includes bibliographic references (ℓ. 70-76)

Thesis (Ph. D.)--University of Nevada, Reno, 2006. / "August, 2006." Includes bibliographical references. Online version available on the World Wide Web.