IMMOBILIZATION OF MERCURY AND ARSENIC THROUGH COVALENT THIOLATE BONDING FOR THE PURPOSE OF ENVIRONMENTAL REMEDIATION

Mercury and arsenic are widespread contaminants in aqueous environments throughout the world. The elements arise from multiple sources including mercury from coal-fired power plants and wells placed in natural geological deposits of arseniccontaining minerals. Both elements have significant negative health impacts on humans as they are cumulative toxins that bind to the sulfhydryl groups in proteins, disrupting many biological functions. There are currently no effective, economical techniques for removing either mercury or arsenic from aqueous sources. This thesis will demonstrate a superior removal method for both elements by formation of covalent bonds with the sulfur atoms in N,N’-Bis(2-mercaptoethyl)isophthalamide (commonly called “B9”). That B9 can precipitate both elements from water is unusual since aqueous mercury exists primarily as a metal(II) dication while aqueous arsenic exists as As(III) and As(V) oxyanions

Quality of Water from Tile Drains in Fields Treated with Poultry Litter in McLean County, Kentucky

Poultry litter (a mixture of feed, manure, and bedding material) is commonly used as a soil amendment to row-crop fields in western Kentucky. Because of feed additives, litter typically has elevated concentrations of contaminants, including metals and anions. These metals and anions can accumulate in the soil and therefore could be transported to surface water through drainage tiles. In order to assess water quality in tile drains, a pilot study was conducted in 2008 in McLean County, Kentucky, in which 10 tile drains and six drainage ditches were sampled for total metals and anions. Seven of the tile-drained fields were amended with poultry litter and three tile-drained fields were not amended. Drainage ditches received discharge from the tile drains. Acidified and unacidified samples were collected for laboratory analysis, and the acidified samples were analyzed for total major and trace metals (aluminum, arsenic, calcium, cadmium, copper, iron, mercury, magnesium, manganese, nickel, lead, and zinc). To determine the association of major and trace metals to suspended material in the water, the unacidified samples were filtered using 0.45- and 0.20-µm filters, and each filtered sample was analyzed for major and trace metals. Mean concentrations for total calcium and magnesium were similar for the amended and unamended field samples. Total aluminum, iron, and manganese concentrations were higher in the amended-field samples than in the unamended-field samples. Total arsenic, cadmium, and mercury concentrations were below the method detection limits for all samples. Total copper and nickel concentrations were higher in the amended-field samples than in the unamended-field samples. Calcium, magnesium, and manganese concentrations did not decrease after samples were filtered. Aluminum and iron concentrations decreased, indicating that these metals are associated with suspended sediment in the tile discharge water. Copper and nickel concentrations did not decrease after the samples were filtered. Chloride, sulfate, and nitrate concentrations were higher in amended-field samples than in unamended-field samples. The mean nitrate concentration for the tile-drain samples from amended fields was above the U.S. Environmental Protection Agency maximum contaminant level of 10 ppm. All phosphate concentrations were below the MDL. Additional sampling is needed to more thoroughly document concentrations and evaluate the impact of potential contaminants associated with poultry litter on the quality of tile-drain water in Kentucky

Identity-by-descent estimation with population- and pedigree-based imputation in admixed family data

BACKGROUND: In the past few years, imputation approaches have been mainly used in population-based designs of genome-wide association studies, although both family- and population-based imputation methods have been proposed. With the recent surge of family-based designs, family-based imputation has become more important. Imputation methods for both designs are based on identity-by-descent (IBD) information. Apart from imputation, the use of IBD information is also common for several types of genetic analysis, including pedigree-based linkage analysis. METHODS: We compared the performance of several family- and population-based imputation methods in large pedigrees provided by Genetic Analysis Workshop 19 (GAW19). We also evaluated the performance of a new IBD mapping approach that we propose, which combines IBD information from known pedigrees with information from unrelated individuals. RESULTS: Different combinations of the imputation methods have varied imputation accuracies. Moreover, we showed gains from the use of both known pedigrees and unrelated individuals with our IBD mapping approach over the use of known pedigrees only. CONCLUSIONS: Our results represent accuracies of different combinations of imputation methods that may be useful for data sets similar to the GAW19 pedigree data. Our IBD mapping approach, which uses both known pedigree and unrelated individuals, performed better than classical linkage analysis

Effect of Ca²⁺ and Zn²⁺ on UO₂ Dissolution Rates

The dissolution of UO₂ in a continuously stirred tank reactor (CSTR) in the presence of Ca²⁺ and Zn²⁺ was investigated under experimental conditions relevant to contaminated groundwater systems. Complementary experiments were performed to investigate the effect of adsorption and precipitation reactions on UO₂ dissolution. The experiments were performed under anoxic and oxic conditions. Zn²⁺ had a much greater inhibitory effect on UO₂ dissolution than did Ca²⁺. This inhibition was most substantial under oxic conditions, where the experimental rate of UO₂ dissolution was 7 times lower in the presence of Ca²⁺ and 1450 times lower in the presence of Zn²⁺ than in water free of divalent cations. EXAFS and solution chemistry analyses of UO₂ solids recovered from a Ca experiment suggest that a Ca–U­(VI) phase precipitated. The Zn carbonate hydrozincite [Zn₅(CO₃)₂(OH)₆] or a structurally similar phase precipitated on the UO₂ solids recovered from experiments performed in the presence of Zn. These precipitated Ca and Zn phases can coat the UO₂ surface, inhibiting the oxidative dissolution of UO₂. Interactions with divalent groundwater cations have implications for the longevity of UO₂ and the mobilization of U­(VI) from these solids in remediated subsurface environments, waste disposal sites, and natural uranium ores

Oxidative dissolution of biogenic uraninite in groundwater at Old Rifle, CO

Reductive bioremediation is currently being explored as a possible strategy for uranium-contaminated aquifers such as the Old Rifle site (Colorado). The stability of U(IV) phases under oxidizing conditions is key to the performance of this procedure. An in situ method was developed to study oxidative dissolution of biogenic uraninite (UO2), a desirable U(VI) bioreduction product, in the Old Rifle, CO, aquifer under different variable oxygen conditions. Overall uranium loss rates were 50–100 times slower than laboratory rates. After accounting for molecular diffusion through the sample holders, a reactive transport model using laboratory dissolution rates was able to predict overall uranium loss. The presence of biomass further retarded diffusion and oxidation rates. These results confirm the importance of diffusion in controlling in-aquifer U(IV) oxidation rates. Upon retrieval, uraninite was found to be free of U(VI), indicating dissolution occurred via oxidation and removal of surface atoms. Interaction of groundwater solutes such as Ca2+ or silicate with uraninite surfaces also may retard in-aquifer U loss rates. These results indicate that the prolonged stability of U(IV) species in aquifers is strongly influenced by permeability, the presence of bacterial cells and cell exudates, and groundwater geochemistry

Correction to Oxidative Dissolution of Biogenic Uraninite in Groundwater at Old Rifle, CO

Correction to Oxidative Dissolution of Biogenic Uraninite in Groundwater at Old Rifle, C