Browsing by Subject "environment"
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Item Biomarkers of Exposure to Foodborne and Environmental Carcinogens: Enterosorbent Intervention in a High Risk Population(2011-10-21) Johnson, Natalie MalekThe need to assess human exposures to foodborne and environmental carcinogens, particularly in populations at high risk for cancer and disease, has led to the development of chemical-specific biomarkers. Sensitive biomarkers for aflatoxin and polycyclic aromatic hydrocarbons (PAHs) have been useful in providing information on population exposure and reducing associated public health impacts. Aflatoxins are fungal metabolites found in a variety of foods. Among these toxins, aflatoxin B1 (AFB1) is the most predominant and hepatocarcinogenic. Acutely, AFB1 can cause disease and death, necessitating safe and effective intervention strategies. Inclusion of NovaSil (NS) clay in the diet represents a practical, sustainable approach. NS has been shown to prevent aflatoxicosis in multiple animal species by binding aflatoxins in the gastrointestinal tract, reducing toxin bioavailability. Co-exposure to PAHs, hazardous environmental contaminants, has been shown to increase the risk for hepatocellular carcinoma (HCC). Therefore, objectives of this research were to utilize biomarkers to assess aflatoxin and PAH exposures in susceptible populations in Ghana and the U.S. and to evaluate the safety and efficacy of NS intervention in Ghana (a population at risk for aflatoxicosis). After 3-month intervention with 3.0g NS/day, median aflatoxin M1 (an AFB1 metabolite) was significantly reduced (up to 58 percent) compared to the placebo group. Furthermore, no significant differences were found in levels of nutrient minerals between NS and placebo groups at baseline and 3-months suggesting NS can be used to effectively sorb AFB1 without affecting serum concentrations of important minerals. PAH biomarker results showed participants in Ghana were significantly exposed to high levels of PAHs based on the presence of 1-hydroxypyrene (1-OHP) in the majority of urines (98.9 percent). NS treatment had no effect on 1-OHP levels, further confirming the preferential binding of aflatoxins by NS. U.S. population data from a Hispanic community in Texas with an elevated incidence of HCC demonstrated a lower percentage and level of aflatoxin and PAH biomarkers. Aflatoxin M1 excretion, however, was associated with increased consumption of certain foods prone to aflatoxin contamination; thus, some individuals may be more vulnerable to exposure and associated interactions that increase the risk for HCC (e.g., PAHs or hepatitis infection).Item Community environments and walking-to-school behaviors: multi-level correlates and underlying disparities(2009-05-15) Zhu, XuemeiWalking can be a safe, healthy, and affordable mode of school transportation. However, most students today do not use walking for their school travel. More research is needed to understand the correlates of walking to or from school and to identify effective interventions. This is a cross-sectional study of 73 public elementary schools in the Austin Independent School District of Texas. The first phase used geographic information systems and field audits to examine school-level disparities in the environmental support for walking in schools? attendance areas. The second phase involved surveys of students? parents or guardians to identify the multi-level correlates of using walking as their children?s typical school travel mode. In the first phase, results from analyses of variance and linear regressions indicated the existence of disparities. Lower economic status of student population was associated with poorer street conditions (e.g., maintenance, visual quality, amenities, and perceived safety), shorter distances to school, and lower traffic volumes. Higher percentage of Hispanic students within a school was associated with increased danger from traffic and crime and more sidewalks, greater population density, and mixed land uses. The second phase used binary logistic regressions to predict walking to or from school. Among the personal and social factors, parents? education, car ownership, personal barriers, and school bus availability were negative correlates, while parents? and children?s positive attitude and regular walking habit and supportive peer influences were positive correlates. Of the physical environmental factors, long distance and safety concerns were the strongest negative correlates, followed by the presence of highways or freeways, convenience stores, office buildings, and bus stops en route. In conclusion, environmental interventions are needed to develop centrallylocated neighborhood schools, barrier-free attendance areas, and well-maintained pedestrian infrastructure. Disparities and fine-grained differences are found in the environmental support for walking. A high priority for low-income, Hispanic children and interventions tailored for specific contexts and populations appear necessary. Safety improvement is indispensible in terms of both traffic and crime and should be supplemented with educational programs that target both parents and children. Finally, multi-agency collaborations are needed at the policy level to support and facilitate these multi-level interventions.Item Interaction of temperature, dissolved oxygen and feed energy on ecophysiological performance of juvenile red drum(Texas A&M University, 2008-10-10) Fontaine, Lance PierreThe red drum (Sciaenops ocellatus) is important for recreational fishing and aquacultural production in Texas' coastal waters and elsewhere in the nearshore Gulf of Mexico and in subtemperate to subtropical areas of the western North Atlantic Ocean. I performed indoor-tank and outdoor-pond experiments, in conjunction with automa ted respirometry and ecophysiological modeling, to assess interacting effects of temperature, dissolved-oxygen concentration (DO) and feed energy density on survival, growth, metabolism, and other measures of juvenile red drum performance. The main objective was to test an energy/metabolism tradeoff hypothesis, which states that growth of fish exposed to high temperatures can be limited by available feed energy; whereas, growth of fish exposed to lower temperatures can be limited by their metabolic capacity to exploit available feed energy. Also, I examined the influence of DO on this relationship and evaluated the effects of cyclical regimes of temperature and DO on fish performance. Insights from laboratory-based feeding trials were incorporated in experiments conducted in hatchery ponds to assess effects of oxygen supplementation and dietary additives - nucleotides and prebiotics - on performance in a more natural setting. In examining these issues, various technologies were developed. These included a computer-based apparatus for autonomously inducing cyclical regimes of temperature and DO in experimental tanks over an extended period of time. Additionally, I developed a soft feed with low energy-density to simulate natural forage. Experimental results supported the principal research hypothesis: At high temperature and DO, ecophysiological performance of juvenile red drum was enhanced by feeding to satiation with a high-energy feed (15.9 kJ/g) versus with a foragesimulating feed having lower energy density (4.1 kJ/g). Cyclical regimes of temperature and DO - as imposed in my particular laboratory experiments -did not impart growth benefits; however, the potential for enhanced growth via an appropriate cyclical environmental regime remains intact. Results from outdoor-pond experiments were consistent with laboratory results; however, the strong positive effect of feed energy density overwhelmed potential effects of dietary additives or oxygen supplementation on growth.Item Our Place in Nature: Toward a Heideggerian Ethos of the Environment(2013-08-02) DeLaFuente, Crystal ZebaThis thesis aims to show that Martin Heidegger?s notion of fundamental ontology can serve as the foundation for a new approach to environmental ethics. The thesis begins with a brief introduction to the traditional approaches of environmental thought and a description of how Heidegger?s interpretation of human existence as Dasein provides a new perspective from which to approach questions of the fitting relation between human beings and the nonhuman world. While traditional environmental thought approaches nature primarily as the object of modern science and technology, Heidegger?s thought allows nature to become meaningful for human beings as an important part of their everyday lives. The first chapter begins with an examination of the wilderness and environmental justice debates and argues that Anglo-American environmental thought has yet to understand and define the natural environment in a way that encompasses the needs of both human and nonhuman life. Heidegger?s existential analytic of Dasein describes human existence in a way that demonstrates its interconnectedness with the nonhuman world and can be used to rethink the fitting place of human existence within the natural environment. The second chapter demonstrates that Heidegger?s critique of the metaphysical foundations of modern science and technology clears the way for a renewed understanding of the interconnectedness of human and nonhuman life. Heidegger?s critique demonstrates that an authentic understanding of human existence necessarily entails a new approach to interpreting being. The final chapter of the thesis analyses Heidegger?s retrieval of the early Greek understanding of being as phusis together with Heidegger?s notion of poetic dwelling in order to provide a new perspective for interpreting the scope of a fitting relation between human beings and natural environment. Heidegger?s thought demonstrates that the natural environment must be understood as an essential condition of human existence and can thereby allow human beings to interpret the nonhuman world in a way that would encompass the needs of both human and nonhuman life.Item Resource portfolio management: bundling process(2009-05-15) Worthington, William JohnManagers within firms seek to align their portfolio of capabilities to best respond to their competitive environment. Processes used by firms to acquire resources, bundle those resources into capabilities, and then leverage those capabilities to obtain competitive advantage are of interest to scholars and practitioners alike. In this study I explore the bundling process and how firms create advantage from its use in different environmental conditions. Using policy capturing survey techniques analyzed with hierarchial linear modeling while manipulating environmental contexts of dynamism, munificence, and punctuated threats, I observe how firms vary their resource bundling processes to create advantage and improve performance. For each combination of environmental condition, hypotheses are presented and tested with respect to firm response. Due to a lack of differentiation between the three bundling sub-processes, several proposed hypotheses were not testable and thus, unsupported. Current theory details three bundling sub-processes; however, I demonstrate evidence that fewer or greater numbers of sub-processes may be required to capture the bundling process. Other evidence suggests that firms do alter bundling sub-processes in response to changing conditions of munificence, but fail to do so during punctuated events.Item Transports of Polymer Nanomedicine in the Environment(2013-11-14) Zhang, MingWith increasing production and commercial use of polymer nanomedicine and a lack of regulation to govern their disposal, polymer nanomedicine may enter into soils and ultimately into ground water system. In this dissertation, adsorption of polymeric nanoparticulate drug delivery system (PNDDS) in the environmental surface as well as uptake of nanomedicine into plants was investigated. Cellulose surface and silica surface were chosen as environmental surfaces and ryegrass was chosen as a plant. The adsorption of PNDDS onto cellulose and silica surface was studied by quartz crystal microbalance with dissipation (QCM) and atomic force microscopy (AFM). Uptake of PNDDS into ryegrass was investigated by spectrofluorometry (SFM), confocal microscopy, scanning electron microscopy (SEM) and cross sectional transmission electron microscopy (TEM). It is found that PNDDS can partially irreversibly adsorb on cellulose and silica surface. After adsorption, PNDDS may deform, disintegrate, or keep the same size depended on properties of PNDDS and PNDDS/surface interaction. Uptake of PNDDS into ryegrass was observed and PNDDS was found both in root cell and intercellular space. PNDDS could transport up to stem of ryegrass but not leaf. Adsorption onto root surface is the rate-determined step of the uptake process. This dissertation represents an important step in understanding environmental impact of polymer nanomedicine. This is very important considering that PNDDS on and in the plants may later be consumed by animals and bacteria and accumulate in their bodies, and can adversely influence environmental health. Also silica/cellulose surface and plants may also be used to treat waste water with PNDDS. Transport behavior and kinetics of PNDDS onto environmental surface studied in this dissertation also could guide to study transport behavior of the same type or other types of polymer nanomedicine in similar or other environmental systems.