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No description available.

Heavy metal (HM) containing quantum dots (Qdots) are increasingly used in commercial products due to their unique electronic, optoelectronic, optical and magnetic properties. Once disposed to the landfill, environmental weathering is likely to compromise HM Qdot integrity, leading to release of heavy metal ions. To minimize any negative environmental impact of HM Qdots, there is an increasing demand for developing HM free or environmentally-friendly surface modified HM Qdot alternatives. In this study, synthesis of HM free ZnS:Mn/ZnS and surface modified HM CdS:Mn/ZnS Qdots (using N-acetylcysteine, NAC, and Dihydrolipoic acid, DHLA) and their potential toxicity assessment using E. coli as a model system is reported. NAC and DHLA are known antioxidants and therefore expected to reduce HM induced toxicity and improve colloidal stability of Qdots. All Qdots were synthesized at room temperature using a reverse micelle microemulsion method. Qdots were fully characterized using UV-visible absorption spectroscopy, fluorescence emission spectroscopy, zeta potential, Nuclear Magnetic Resonance spectroscopy (NMR) and High Resolution Transmission Electron Microscopy (HRTEM). Qdot environmental weathering was simulated by treating Qdots with concentrated acid (6N HCl). Qdot toxicity was evaluated on E. coli growth and viability using growth curves, turbidity and bactericidal assays (CFU). Results show that Zn based Qdots exhibit reduced toxicity on E.coli growth and viability when compared to Cd based Qdots. In addition, surface modification with NAC and DHLA minimized toxicity of Cd based Qdots. In summary, Zn based Qdots appear to be more environmental-friendly than Cd based Qdots

The kinetics of Escherichia coli inactivation were studied using ultraviolet (UV) radiation, ozone, and UV and ozone (UVO) in combination in a batch reactor at varying pH levels (6, 7, and 8) and at a constant temperature of 25°C. The inactivation kinetics for all three treatment processes was pseudo first order, and the reaction rate constants were considered to be additive such that a combined reaction rate could be obtained by adding the kinetic rates of the processes applied and numerically small rates could be neglected in the computation of the combined rate. Statistical tests (ANOVA and student's t-test) performed on the inactivation data indicated no apparent effect of pH on the kinetics of the processes. It was found that the UVO process was the most efficient in inactivating E. coli. The increase in the inactivation rate with the UVO process is attributed to synergetic activity of UV and ozone which results in the generation of hydroxyl radicals from ozone decomposition.

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No description available.

Bcl-XL is a membrane-associated protein that inhibits programmed cell death (apoptosis) in mammalian cells. Very little is known about the membrane topology of Bel-XL or how its association with membranes contributes to its function. It was the aim of this thesis to use fluorescence spectroscopy to investigate the location of a specific amino acid ofBcl-XL relative to the membrane. Bel-XL purified from E. coli could bind both to large unilamellar vesicles and endoplasmic reticulum (ER) microsomes isolated from canine pancreas. A cysteine residue at position 151 in Bcl-XL could be covalently labelled with the environmentally sensitive fluorescent molecule NBD. Emission intensity measurements in the presence and absence of membranes, combined with aqueous and lipophilic quenching experiments, indicate that Cys 151 is inserted into the interior of the membrane bilayer when Bcl-XL is bound to membranes. The methods outlined in this thesis form the basis for an experimental system that can be used to determine the membrane topology ofBclXL under a variety of conditions. / Thesis / Master of Science (MSc)

Sources of fecal pollution were evaluated as a function of sampling frequency with stream samples from Mill Creek, Montgomery County, VA. Samples were collected monthly for one year, plus weekly for four consecutive weeks during seasonal high flows (March), and seasonal low flows (September-October), plus daily for seven consecutive days within the weekly schedules. Thirty stream samples were collected from each of two sites (60 total) in Mill Creek, and 48 isolates of E. coli per sample (total of 2,880 stream isolates) were classified by source using antibiotic resistance analysis (ARA) and comparing the resulting patterns against a known-source E. coli library (1,158 isolates). The same process was performed with enterococci isolates against an enterococci library (1,182 isolates). The average rate of correct classification (ARCC) for the E. coli library with a three-way split (human, livestock, and wildlife) was 89.0%, and the ARCC of the species-specific E. coli library (cattle, deer, goose, human, misc. wildlife) was 88.9%. The ARCC of the enterococci library with a three-way split was 85.3%, and the ARCC of the species-specific enterococci library was 88.1%. The results did not justify the need for daily or weekly sampling, but indicated that monthly was adequate (quarterly and every-other-month were not). There was a seasonal effect as the human signature was highest during high flow while the livestock signature dominated during low flow. The results also indicated that sampling should be done over a period of time that includes both seasonal wettest and driest periods (at least 8 months). / Ph. D.

High levels of fecal indicator bacteria (e.g. E. coli) are the leading cause of identified surface water impairments in the United States. The US Clean Water Act of 1972 requires that jurisdictions establish priority rankings for impaired waterways and develop a Total Maximum Daily Load (TMDL) plan for each. Although past research indicates that the risk of illness to humans varies by source of fecal contamination, current watershed assessments are developed according to total concentration of indicator bacteria, with all sources weighed equally. A stochastic model using Quantitative Microbial Risk assessment (QMRA) principles to translate source-specific (e.g. human, livestock) daily average concentrations of E.coli into a daily average risk of gastroenteritis infection was developed and applied to Pigg River, an impaired watershed in southern Virginia. Exposure was calculated by multiplying a ratio of source related reference pathogens to predicted concentrations of E.coli and a series of qualifying scalars. Risk of infection was then determined using appropriate dose response relationships. Overall, human and goose sources resulted in the greatest human health risk, despite larger overall E.coli loading associated with cattle. Bacterial load reductions specified in the Pigg River TMDL were applied using Hydrological Simulation Program- FORTRAN (HSPF) to assess the effect these reductions would have on the risk of infection attributed to each modeled bacterial source. Although individual risk sources (neglecting geese) were reduced below the EPA limit of 8 illnesses per 1000 exposures, the combined risk of illness varied between 0.006 and 64 illnesses per 1000 exposures. / Master of Science

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