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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
171

Elucidating the Impact of Biosolids-Derived Antimicrobials on Denitrifying Microbial Community Function and Structure in Agricultural Soil

Holzem, Ryan Michael January 2014 (has links)
<p>More than 50% of wastewater biosolids are applied to agricultural fields as fertilizer in the U.S. This technique has been used for decades as a widely accepted beneficial reclamation method for biosolids, which meet the established regulatory levels for nutrients, metals, and pathogens. A major drawback to land application is the potential environmental release of non-regulated organic contaminants, which accumulate in biosolids during the wastewater treatment process. Recent studies have been performed to identify and quantify the presence of emerging contaminants in biosolids, and others have investigated the effects of compounds already identified as `priority pollutants' and whose use is waning. However, there is limited research on the effect of emerging organic contaminants on soil microbial ecology and nutrient cycling. Because many of the compounds found in biosolids are specifically designed to elicit biological modifications (e.g., antimicrobials), there is a risk that these compounds will disrupt microbial soil functions, decrease soil productivity, and ultimately affect the long term viability of these ecosystems, resulting in unforeseen economic and social costs. Therefore, there is a clear need to characterize the effects of novel contaminants on soil health.</p><p>This dissertation was divided into three distinct parts examining the impacts of emerging organic contaminants on soil microbial ecology with increasing complexity to better reflect environmental conditions. To assess the ecological impacts, the functional endpoint of denitrification was selected because it provides a vital indication of soil health. Denitrifying bacteria play a critical role in this process, and thus, were used as indicator organisms for determining contaminant ecotoxicological potential. Furthermore, antimicrobial agents (a.k.a., bactericides or biocides) were selected as model contaminants because they are designed specifically to deactivate microorganisms, are heavily used in the U.S with over $1 billion in yearly sales, and have been measured in biosolids.</p><p>Overall, the objectives of this dissertation were to: 1) develop a rapid, high-throughput functional assay that measured denitrification inhibition for screening potential ecological impacts of biosolids-derived antimicrobial agents, 2) determine the potential effects of common and emerging biosolids-derived antimicrobial agents on denitrification by a model soil denitrifier, Paracoccus denitrificans PD1222, 3) examine the impacts of the most commonly used antimicrobial, triclosan (TCS), on wastewater treatment efficiency in bench scale sequencing batch reactors (SBRs) coupled with anaerobic digesters, 4) examine the impacts of biosolids aged and spiked with TCS on denitrification under simulated agricultural soil conditions, and 5) evaluate potential impacts of TCS in `traditional' biosolids on denitrification in agricultural soil under field conditions.</p><p>The first phase of research pertaining to Objectives 1 and 2 examined the baseline interactions between biosolids-derived antimicrobial agents and soil microbial ecology. However, to isolate the effect of an individual contaminant from the myriad of contaminants found in biosolids, there was a need for developing a rapid, high-throughput method to evaluate general ecotoxicity. In the first part of this dissertation, we developed a novel assay that measured denitrification inhibition in a model soil denitrifier, Paracoccus denitrificans Pd1222. Two common (TCS and triclocarban) and four emerging (2,4,5 trichlorophenol, 2-benzyl-4-chlorophenol, 2-chloro-4-phenylphenol, and bis(5-chloro-2-hydroxyphenyl)methane) antimicrobial agents found in biosolids were analyzed as model contaminants. Overall, the assay was reproducible and measured impacts on denitrification over three orders of magnitude exposure. The lowest observable adverse effect concentrations (LOAECs) were 1.04 &mu;M for TCS, 3.17 &mu;M for triclocarban, 0.372 &mu;M for bis-(5-chloro-2-hydroxyphenyl)methane, 4.89 &mu;M for 2-chloro-4-phenyl phenol, 45.7 &mu;M for 2-benzyl-4-chorophenol, and 50.6 &mu;M for 2,4,5-trichlorophenol. Compared with gene expression and cell viability based methods, the denitrification assay was more sensitive and resulted in lower LOAECs. Of the six compounds examined, four resulted in LOAECs that were below or within an order of magnitude of concentrations that were measured in the environment, indicating potential ecological impacts.</p><p>In the second part of the dissertation, the impacts of emerging contaminants were examined first under laboratory conditions mimicking wastewater treatment processes (Objective 3) and then agricultural fields (Objective 4). For this phase, TCS, which is the most widely used antimicrobial agent and identified in the first phase for potential ecological impacts, was used as the model contaminant. To mimic wastewater treatment processes, bench scale SBRs coupled with anaerobic digesters were set up and operated. The SBRS and digesters were seeded with activated and anaerobically digested sludge from the North Durham Water Reclamation Facility (NDWRF, Durham, NC). Reactors were fed synthetic wastewater with or without 0.73 &muM of TCS. Samples were taken periodically to monitor chemical oxygen demand (COD), ammonium (NH<sub>4</sub><super>+</super>), nitrate (NO<sub>3</sub><super>-</super>), nitrite (NO<sub>2</super>-</super>), total suspended solids (TSS), volatile suspended solids (VSS), dissolved oxygen (DO), and phosphate (PO<sub>4</sub><super>3-</super>) and pH. In addition, biomass samples were collected for DNA extraction and microbial community analysis using terminal restriction fragment length polymorphism (T-RFLP) of 16S SSU rDNA. Methane production was also monitored for the anaerobic digesters. In addition, the final digested biosolids that were generated from the SBRs fed with and without TCS were analyzed for TCS concentration, TSS, VSS, TKN, phosphorus (as P<sub>2</sub>O<sub>5</sub>), potassium (as K<sub>2</sub>O), and pH. Overall, biological processes associated with nitrogen removal (nitrification and denitrification), were impacted by TCS entering the SBRs regardless of the starting microbial community. Both of the SBRs that were not receiving TCS reached steady-state at greater than 92% NH<sub>4</sub><super>+</super>, removal within the first week of operation, whereas the SBRs receiving TCS took 42 and 63 days to reach steady-state removal at that level. However, while NH<sub>4</sub><super>+</super> removal was temporarily inhibited, elevated levels of NO<sub>3</sub><super>-</super> and NO<sub>2</sub><super>-</super> in the effluent of the TCS fed SBRs, suggested longer-term impacts on nitrite oxidizing bacteria (NOB) and denitrifiers. After Day 58, the NO<sub>3</sub><super>-</super> effluent concentration for the SBRs receiving TCS was 3.9 ± 0.16 mg/L, which was 2.4 times greater than the NO<sub>3</sub><super>-</super> effluent of the SBRs not receiving TCS (1.7 ± 0.08 mg/L). Similarly, after Day 58, the NO<sub>2</sub><super>-</super> effluent of the SBRs receiving TCS reached a steady-state concentration of 8.7 ± 0.75 mg/L. The mean NO<sub>2</sub><super>-</super> concentration in the controls after Day 58 was 7.7 times lower at 1.1 ± 0.78 mg/L, but was still trending towards 0 when the reactors were stopped. No inhibition was observed for COD and PO<sub>4</sub><super>3-</super> removal. In addition, non-metric multidimensional scaling (NMS) ordination analysis showed that the microbial communities between SBRS fed with and without TCS were similar on Day 0, but increased in difference to Day 41, around when the major changes in nitrification were observed. After a slight increase in similarity between the control and TCS SBR microbial communities on Day 41, the communities increased in difference to Day 63.</p><p>To mimic agricultural field conditions, containers of soil were amended with the biosolids generated from the SBRs. The containers were maintained in a growth-chamber to simulate field lighting and watering conditions. Three biosolids treatments were examined: 1) biosolids generated from the SBRs not fed TCS, but that still had low backgrounds of TCS (a.k.a., Control Biosolids); 2) biosolids generated from the SBRs fed with TCS (a.k.a., Aged TCS Biosolids); and 3) biosolids that were generated by the SBRs not fed TCS, but spiked with TCS 24 h before application (a.k.a., Spiked TCS Biosolids). Alfalfa was planted in half of the containers receiving the Control and Aged TCS Biosolids to assess differences due to vegetation. To assess the overall ecotoxicity of biosolids aged and spiked with TCS, the function, abundance, and diversity of the soil denitrifying communities were examined. The impacts on total bacteria abundance and diversity were also examined for comparison. Specifically, the denitrifying enzyme activity (DEA) assay was used to measure functional impacts, quantitative polymerase chain reaction (qPCR) was used to measure impacts on abundance, and T-RFLP was used to measure impacts on diversity. Correlations between these methods were also examined for possible interactions between denitrifier function and community structure and to provide insight into targets of inhibition. Lastly, a denitrification inhibition score was developed to quantify global impacts of TCS on denitrification. The containers with plants that received biosolids aged with and spiked with TCS showed potential long-term inhibition based on measurement of soil denitrification at 26.9 ± 4.6 &mu;g/kg and 68.6 ± 26.9 &mu;g/kg of TCS, respectively. Denitrifier abundance and diversity, however, were more sensitive to TCS in biosolids and inhibition was observed throughout the experiment, with maximum inhibition on Days 7 and 28. Inhibition of denitrifier abundance and diversity was observed at TCS concentrations as low as 17.9 ± 1.93 &mu;g/L, which was about 10 to 3000 times lower than concentrations reported by other studies that showed impacts on other functional endpoints (i.e., respiration, phosphatase activity, NO<sub>3</sub><super>-</super> and NO<sub>2</sub><super>-</super> production, and Cy17 stress biomarker abundance), even after taking pH into account. Five significant correlations were developed, three of which related qPCR and the DEA assay, or abundance and activity. However, the analyses that were correlated did not yield the same results as far as significant inhibition in the presence of TCS. Thus, while the results suggested some relatedness between activity, abundance, and diversity, the results generally support the use of multiple methods to determine the ecotoxicity of biosolids-derived organic contaminants. As a result, a denitrification inhibition score was developed that took into account all three methods to determine the overall ecotoxicity of TCS in biosolids. Overall, the denitrification inhibition score showed that denitrification was inhibited by both biosolids that were aged and spiked with TCS over the extent of the 84 day experiment, but maximum inhibition occurred after a week to about a month. While the denitrification inhibition score indicated that the TCS in the biosolids aged with TCS was less bioavailable than in the spiked biosolids, the impacts of the aged and spiked biosolids could have also been due to differences in TCS concentrations.</p><p>Objective 5 consisted of a long-term soil sampling campaign on four agricultural fields receiving Class B municipal biosolids. Soil samples were taken before and after biosolids application and were analyzed to elucidate potential impacts of TCS in the biosolids on denitrification. Again, to assess the overall impacts of TCS on the soil denitrifying community, the DEA assay, qPCR, and T-RFLP were used to measure impacts on function, abundance, and diversity, respectively. Similar to Objective 4, the analysis included an examination of potential correlations between denitrifying community structure and function, and quantification of global impacts using the denitrification inhibition score. As expected, the results in this pilot-study reflected the complexity of the system that was analyzed and many more samples, which account for variables including, but not limited to soil characteristics, biosolids characteristics, biosolids application rates, and chemical composition and quantities, would be needed to show any statistically significant differences. Nevertheless, several key results were obtained. Again potential long-term inhibition of denitrification was observed using the DEA assay, however the effects of exhaustion of resources, such as NO<sub>3</sub><super>-</super>, or significant changes in the local environment were suspected, but could not be verified. Inhibition was also observed for denitrifier abundance, but little to no inhibition was observed when examining the relative number of denitrifying species. Thus, while the abundance of denitrifiers was reduced, and denitrification was eventually depressed, the number of species in the soil remained constant. When looking at the denitrification inhibition score, which took all three measurements into account, increased inhibition over time was observed with the exception of the measurements on Days 30 and 103, which indicated overall, but weak inhibition of denitrification by the application of biosolids. NMS ordinations showed no correlation between the shift in denitrifying microbial community and TCS. Because of the complexity of the soil and biosolids and because of the myriad of contaminants likely in the biosolids, the results may not be significant and a more in-depth study was recommended.</p><p>Overall, the results presented in this dissertation provide a systematic evaluation of the effects of biosolids-derived TCS on agricultural soil microbial ecology. First, it was demonstrated that statistically significant inhibition of denitrification could be used as a potential indicator of biosolids-derived emerging organic contaminant ecotoxicity. The denitrification assay that was developed was then used to analyze ecotoxicological potential of six emerging biosolids-derived antimicrobial agents, and found inhibition of denitrification at environmentally relevant concentrations. The most widely used antimicrobial agent, TCS, was further shown to inhibit wastewater treatment processes, as well as, denitrification in simulated agricultural conditions after being aged with and spiked into biosolids. In addition, evidence showing potential inhibition of denitrification by TCS in `traditional' biosolids under field conditions was also obtained. Based on these results, this dissertation asserts that biosolids-derived emerging organic contaminants pose a potential risk to agricultural soil microbial ecology and overall soil health. Future studies, however, are needed to examine the impacts of other contaminants that might be flagged with the assay developed in this dissertation under more complex conditions mimicking the environment. Furthermore, other research is needed to examine the role microbial communities play in the bioavailability of emerging contaminants, especially TCS, and a more extensive, in-depth study is needed to characterize the individual impacts of emerging contaminants on soil microbial communities under field conditions.</p> / Dissertation
172

Using refurbished turbines to provide affordable wind energy: A case study in Africa

Montenegro Borbolla, Ivan January 2015 (has links)
When a wind farm is repowered, decommissioned turbines are discarded. This creates a stock of wind turbines that can be acquired for a fraction of the original cost, and refurbished. Taking advantage of the reduced price and the ruggedness of first generation wind turbines, new markets for sale of wind energy can be explored. This thesis first analyses the repowering background of Germany, Denmark, and other European countries, where transition to repowered or “second generation” wind farms is taking place. Then, a number of feasibility studies are reviewed to create a study framework, which will allow in-depth study of suitable energy markets. Using this framework, the suitability of four countries is analysed in detail: Djibouti, Madagascar, Mozambique, and Tanzania. Two countries are selected to perform a total of 6 site studies: Djibouti and Tanzania. Using WindPro 2.9, six model wind farms are simulated. A financial model is built, based on an NREL study, to analyse the economic viability of wind farms. Using the financial model, the levelized cost of energy is obtained, and used to evaluate the competitiveness of the model wind farms. A sensitivity study is carried out to identify the major influences on the LCOE. Using the cost data, the cost competitiveness of the proposed wind farms is discussed, including competitiveness in the target markets, and a cost comparison with commercial wind farms with new turbines is performed. Five out of six proposed wind farms are competitive in price in the target markets, and all achieve an average installation cost per kW of one third of conventional wind farms, while producing energy in the low range of commercial projects, and even lower for sites with excellent wind resources.
173

Angola - an emerging market with potential and risk : A case study of four Swedish Multinational firms

Ringlander, Erik, Viggeborn, Anna, Andersson, Rikard January 2008 (has links)
<p>The purpose of this study is to examine how the learning process of four Swedish firms in the emerging market Angola works. Theoretical framework developed identified different theory streams such as; experiential learning, networks and incremental steps derived from internationalization theory. These theories we believed would explain the learning process in a market characterized by growth and risk factors. We have interviewed managers operating in Angola at four Swedish MNC‟s, in which we identified patterns of learning between the firms. Having analyzed elements from empirical and theoretical framework it can be clearly seen that firms learn through experiential learning and networks. These two factors can take different pattern forms as it depend on the MNC‟s industry and the firms experience from previous activities in Angola and nearby countries i.e. incremental steps. Added to the developed framework are previous experience and the institutions in the market. These five elements are interrelated, however, firms can learn about the market in a more effective way by understanding the institutional factors that are present.</p>
174

ABB’s Internationalization in the Emerging Chinese Market : Entry Mode and Market Development Progress

Phan Van, Thang, Xin, Zhang January 2008 (has links)
<p><p>The aim of the thesis is to describe the entry mode choice and market</p><p>development progress of the successful MNC ABB in the specific</p><p>emerging market China. The authors also want to use theories in the</p><p>master course of International Business and Entrepreneurship to</p><p>explain the internationalization of one specific company ABB</p></p>
175

Elucidation of Dissolved Organic Matter Interactions with Model Contaminants of Emerging Concern

Hernandez Ruiz, Selene January 2011 (has links)
This study examined the interaction of model cationic, neutral and anionic endocrine disrupting compounds, pharmaceuticals and personal care products (EDC/PPCPs) with bulk and fractionated freshwater and waste water dissolved organic matter (DOM). The chemical composition of the freshwater DOM (Suwannee River, GA, SROM) proved to be rich in plant-derived hydrophobic aromatics, while the wastewater DOM (WWOM) contained a greater proportion of microbial biomolecular products, presumably resulting mainly from human waste. Studies focused on the fluorescence quenching of excitation-emission matrices (EEMs) of WWOM indicated that interaction with bis-phenol A (BPA), carbamazepine (CBZ), and ibuprofen (IBU) occurred preferentially with soluble protein-like and fulvic acid-like constituents. However, upon introduction to bulk SROM, BPA and CBZ were observed to quench humic acid-like regions of the EEMs, while negatively charged ibuprofen preferentially quenched the protein-like and fulvic acid components irrespective of DOM source and/or fraction. Despite this evidence of EDC/PPCP interactions with both DOM types, the strength of bonds formed was generally not sufficient to preclude full recovery and quantification of all three contaminants by liquid chromatography tandem mass spectrometry (LC-MSMS). An important exception, however, was for the hydrophilic acid fraction (HiA) of both DOM types, whose apparent bonding to cationic CBZ and anionic IBU significantly diminished LC-MSMS recovery. Thus, water sources rich in HiA character might produce a concentration underestimation of ionized EDC/PPCPs even with the use of sophisticated instruments such as LC-MSMS.The results of this research are consistent with the evolving ""supramolecular"" theory of natural organic matter, which postulates that organic matter itself is comprised of fragments of partially degraded biomolecules that are aggregated into ""supramolecular"" structures of apparent higher molar mass via relatively weak electrostatic, hydrophobic, and van der Waals interaction. Our findings suggest that EDC/PPCP contaminants, which comprise many of the same functional groups as waste water and freshwater DOM, may be incorporated into such DOM supramolecular structures, likely via the same types of intermolecular bonding, when they are present in natural waters under environmentally-relevant conditions.
176

Premenstrual Symptoms and Academic Stress in Emerging Adulthood Women

Hulstein, Pamela Lou January 2009 (has links)
Premenstrual symptoms are a universal event during a woman's reproductive life but little is known about the experience of emerging adulthood women aged 18-25 years. The purpose of this study was to determine feasibility of daily symptom data collection via an electronic diary and to examine the relationship between premenstrual symptom perception, severity and distress with academic stress. This sample consisted of 50 women with a mean age of 20(±.9) years living in campus housing of a private undergraduate rural college. Results determined it is feasible to utilize an electronic diary for daily prospective symptom and academic demand data collection. Surprisingly, in this sample of healthy undergraduate women, there were significantly higher numbers of symptoms perceived (7.16±3.8 follicular and 6.18±3.3 luteal, p=.001 and higher distress (.39±.3 follicular and .31±.3 luteal, p=.003) in the follicular phase than in the luteal phase. Academic stress findings indicated mild stress as measured by the Student-life Stress Inventory (Gadzella, 1991) and students overall perceived stress levels fell in the minimal to mild range. The academic demand component of academic stress measured daily frequency and distress associated with assignments, papers, projects/presentation and time studying. Within the follicular phase number of assignments due was significantly correlated to symptom perception and distress (.31, .37, respectively) and the number of projects/presentations due was correlated to symptom distress (.25) at p<.05. There were significant correlations between follicular phase symptom perception and distress, and luteal phase symptom distress with academic demand distress for assignments, papers, projects/presentations and time studying, indicating a relationship between distress components of symptom experience and some components of academic stress. These premier results about the relationship between symptom distress and academic stress warrants further exploration and development of a clearer conceptual definition of academic stress and clear and consistent operationalization of this phenomena.
177

ADVANCED OXIDATION OF CHEMICALS OF EMERGING CONCERN: MODELING AND EXPERIMENTAL SIMULATION

Rojas Cardozo, Mario Roberto January 2011 (has links)
Every year, new trace chemicals are detected in natural waters as well as treated wastewater effluents all over the world. Public health and environmental concerns have driven the development of new technologies to treat water and eliminate chemicals that may pose risk to humans and wildlife. This work presents a detailed statistical analysis on the removal of some of the most widely occurring chemicals of emerging concern in wastewater based on information available in the literature. Results show that existing water treatment processes only partially eliminate most of these contaminants. Advanced oxidation processes (AOPs) are some of the technologies that have shown the most promising results for the removal of recalcitrant organics in water. Hydrogen peroxide photolysis (UV/H₂O₂) and Fenton’s reaction are some examples of AOPs that use hydroxyl radicals to oxidize organics. The kinetics of UV/H₂O₂ and Fenton’s reaction were studied from the experimental and mathematical points of view. Comprehensive models with no adjustable parameters successfully accounted for radical initiation via photolysis of H₂O₂ or radical initiation via Fenton’s mechanism; reaction of organic targets such as p-cresol and nonylphenol with hydroxyl radicals; and recombination mechanisms, as well as changes in solution pH due to evolution of carbon dioxide because of target mineralization. The presence of radical scavengers was successfully handled by the models, suggesting that they can be generalized to the treatment of complex matrices. The UV/H₂O₂ model was also extended to solar catalyzed applications. Using an atmospheric solar irradiation model (SMART) and data from the Giovanni-NASA online database, ground-level solar spectral irradiance were obtained and used as model inputs. The kinetic model provided an excellent fit to experimental results obtained with p-cresol and fluorescein targets using no fitted parameters. The UV/H₂O₂ process was also studied in commercial flow-through UV reactors with monochromatic and polychromatic light sources. Organic targets of interest such as pcresol can be degraded effectively in these reactors at relatively low peroxide concentrations. Results with wastewater effluents suggest that these commercial reactors can be used for AOP tertiary treatment as a way to reduce dissolved organic matter and eliminate potential harmful chemicals present in the water.
178

The Effects of Exchange Traded Funds on Emerging Market Equities

McNab, James R 01 January 2013 (has links)
This paper examines the effect capital flows from the introduction of exchange traded funds (ETFs) have on emerging markets. Recent years have seen more capital transfer into emerging markets, and the advantages ETFs offer have helped expedite the process. Increased liquidity and a large diverse collection of holdings help manage the high degree of volatility inherent to these markets. The holdings of the ETFs are tested for returns above their market average for the period surrounding the initial trading date of the fund. Positive effects were seen on individual stocks, but overall the findings suggest no significant mean excess return exists for the period related to the creation of an ETF.
179

Synthetic glucocorticoids in the aquatic environment : their potential impacts on fish

Kugathas, Subramaniam January 2011 (has links)
Human pharmaceuticals have been shown to be entering the aquatic environment in quantities sufficient to produce adverse effects to aquatic organisms, particularly fish. The impacts of synthetic oestrogens have been well documented, but other groups of steroidal pharmaceuticals have not yet been studied. Hence, the present research was designed to study synthetic glucocorticoids (GCs), which are used in large amounts as immunosuppressive and anti-inflammatory drugs. This study involved different approaches, including in silico, in vitro, in vivo and genomics, to assess the effects of GCs on fish. Using reliable data on consumption of GCs in the UK and the LF2000-WQX hydrological model, mean concentrations of GCs in the river Thames were predicted to be in the range from 30 ng/L to 850 ng/L. Mammalian cell lines were transiently transfected with trout corticosteroid receptors (GR1, GR2 and MR) and the transactivation abilities of ten of the most prescribed GCs in the UK were measured in vitro. All tested GCs showed significantly higher activity with GR2 than with GR1. In order to assess the impact of low concentrations of GCs in vivo, two chronic exposure experiments were conducted with adult fathead minnows (Pimephales promelas). Both experiments showed potency-related and concentration-related impacts on various endpoints. There was a concentration-related increase in plasma glucose concentrations and a decrease in blood lymphocyte count. Induction of secondary sexual characters in females suggests a concentration-related masculinisation of fathead minnows. There was a decreasing trend in plasma vitellogenin concentrations in female fish with increasing exposure concentration of GCs. Expression profiles of selected genes (PEPCK, GR and Vtg) in liver also demonstrated concentration-related effects at all three tested concentrations. Hence, it was not possible to define a no effect concentration for the tested GCs. This study probably provides reliable estimates of the likely range of concentrations of GCs in a typical river, impacted by effluent from many sewage treatment plants. The in vitro results indicate that all tested GCs bind to fish GR in a similar manner to that reported for mammalian receptors. The in vivo results suggest that GCs could cause effects at very low (as low as 100 ng/L) concentrations that could be environmentally-relevant. The immunosuppresive effects could make fish susceptible to disease and the reproductive effects may have population-level impacts. It is very likely that the effects of different GCs will be additive, as has been shown for oestrogenic chemicals. Therefore, this study warrants further environmental risk assessment of GCs, especially in mixture scenarios.
180

Evaluation of predators as sentinels for emerging infectious diseases

Meredith, Anna Louise January 2012 (has links)
New and emerging diseases in human and animal populations appear to be predominately associated with generalist pathogens that are able to infect multiple hosts. Carnivores are susceptible to a wide range of these pathogens and can act as effective samplers of their vertebrate prey, which are important reservoirs of many emerging diseases. This thesis evaluates the utility of carnivores as sentinels for pathogens present in their prey by exploration of four selected pathogen-prey-sentinel combinations in three rural study sites of varying habitat in northern England and Scotland over a twenty-two month period (2007-2009). Selected pathogens were Coxiella burnetii, Leptospira spp., Encephalitozoon cuniculi, and rabbit haemorrhagic disease virus (RHDV), selected prey species were wild rodents and rabbits, and selected carnivores were foxes, domestic cats and corvids. Seroprevalence to C.burnetii, Leptospira spp and E.cuniculi was assessed using adapted or novel test methodologies to enable their use for multiple mammalian species, however these were not applicable to corvids. RHDV seroprevalence was not assessed due to low acquisition of rabbit samples. Overall, seroprevalence to all three pathogens was significantly higher in predators than prey, at 24.2% and 12.4 % for C.burnetii, 22.73% and 1.95% for Leptospira spp and 39.06% and 5.31% for E.cuniculi in predator and prey species respectively. A similar pattern was found in all study areas and was consistent irrespective of individual prey or predator species, although serological evidence of exposure to E.cuniculi was not detected in domestic cats in any area. A semi-quantitative assessment of the time and financial costs of the study approach and application to hypothetical examples indicates that sampling carnivores is a much more costeffective approach to pathogen detection than sampling prey. The results indicate that carnivores can act as useful sentinels for broad-scale detection of pathogen presence and relative levels of prevalence in prey and predator populations. Careful selection of predator species and methods of sample acquisition are necessary to maximise their utility, and issues associated with diagnostic test performance and validation must also be acknowledged. Suggestions are made as to how this principle might be applied to future surveillance programmes. In addition, the study is the first report on the seroprevalence of C.burnetii, Leptospira spp and E.cuniculi in multiple wildlife species (field voles, bank voles, wood mice, foxes), the first detection of antibodies to C. burnetii in wildlife and cats, the first detection of antibodies to L mini, L hardjo prajitno and L hardjo bovis in wild rodents, and to L mini in cats, and the first detection of antibodies to E.cuniculi in wild rodents and foxes in the UK.

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