• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 19
  • 5
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 37
  • 37
  • 13
  • 11
  • 6
  • 6
  • 5
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 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.
31

Proximity to Potential Sources and Mountain Cold-trapping of Semi-volatile Organic Contaminants

Westgate, John Norman 13 August 2013 (has links)
If sufficiently persistent, semi-volatile organic contaminants (SVOCs) can travel long distances through the atmosphere from their points of release and become concentrated in cold, remote regions. As air is sampled for SVOCs to establish both their presence and the success of emission reduction efforts, it becomes helpful to determine sampling site proximity to sources and the origin of the sampled air masses. Comparing three increasingly sophisticated methods for quantifying source proximity of sampling locations, it was judged necessary to account for the actual history of the sampled air through construction of an airshed, especially if wind is highly directional and population distribution is very non-uniform. The airshed concept was improved upon by introducing a ‘geodesic’ grid of equally spaced cells, rather than a simple latitude/longitude grid, to avoid distortion near Earth’s poles and to allow for the comparison of airshed shapes. Assuming that a perfectly round airshed reveals no information about sources allows the significance of each cell of an airshed to be judged based on its departure from roundness. Combining air-mass histories with a 2 year-long series of SVOC air concentrations at Little Fox Lake in Canada’s Yukon Territory did not identify distinct source regions for most analytes, although γ-hexachlorocyclohexane appears to originate broadly in north-eastern Russia and/or Alaska. Based on this remoteness from sources, the site is judged to be well suited to monitor changes in the hemispheric background concentrations of SVOCs. A model-based exploration revealed wet-gaseous deposition as the dominant process responsible for cold-trapping SVOCs in mountain soils. Such cold trapping is particularly effective if precipitation rate increases with altitude and if temperature differences along the mountain are large. Considerable sensitivity of the modeled extent of cold-trapping to parameters as diverse as scale, mean temperature, atmospheric particle concentration and time relative to emission maxima is consistent with the wide variety of observed enrichment behaviour. Concentration gradients of polycyclic aromatic hydrocarbons and polychlorinated biphenyls in air and soil measured on four Western Canadian mountains with variable distance from sources revealed source proximity as the main driver of concentrations at both the whole-mountain scale and along individual mountain transects.
32

Proximity to Potential Sources and Mountain Cold-trapping of Semi-volatile Organic Contaminants

Westgate, John Norman 13 August 2013 (has links)
If sufficiently persistent, semi-volatile organic contaminants (SVOCs) can travel long distances through the atmosphere from their points of release and become concentrated in cold, remote regions. As air is sampled for SVOCs to establish both their presence and the success of emission reduction efforts, it becomes helpful to determine sampling site proximity to sources and the origin of the sampled air masses. Comparing three increasingly sophisticated methods for quantifying source proximity of sampling locations, it was judged necessary to account for the actual history of the sampled air through construction of an airshed, especially if wind is highly directional and population distribution is very non-uniform. The airshed concept was improved upon by introducing a ‘geodesic’ grid of equally spaced cells, rather than a simple latitude/longitude grid, to avoid distortion near Earth’s poles and to allow for the comparison of airshed shapes. Assuming that a perfectly round airshed reveals no information about sources allows the significance of each cell of an airshed to be judged based on its departure from roundness. Combining air-mass histories with a 2 year-long series of SVOC air concentrations at Little Fox Lake in Canada’s Yukon Territory did not identify distinct source regions for most analytes, although γ-hexachlorocyclohexane appears to originate broadly in north-eastern Russia and/or Alaska. Based on this remoteness from sources, the site is judged to be well suited to monitor changes in the hemispheric background concentrations of SVOCs. A model-based exploration revealed wet-gaseous deposition as the dominant process responsible for cold-trapping SVOCs in mountain soils. Such cold trapping is particularly effective if precipitation rate increases with altitude and if temperature differences along the mountain are large. Considerable sensitivity of the modeled extent of cold-trapping to parameters as diverse as scale, mean temperature, atmospheric particle concentration and time relative to emission maxima is consistent with the wide variety of observed enrichment behaviour. Concentration gradients of polycyclic aromatic hydrocarbons and polychlorinated biphenyls in air and soil measured on four Western Canadian mountains with variable distance from sources revealed source proximity as the main driver of concentrations at both the whole-mountain scale and along individual mountain transects.
33

Analysis of PAH and PCB Emissions from the Combustion of dRDF and the Nondestructive Analysis of Stamp Adhesives

Poslusny, Matthew 05 1900 (has links)
This work includes two unrelated areas of research. The first portion of this work involved combusting densified refuse derived fuel (dRDF) with coal and studying the effect that Ca(0H)2 binder had on reducing polycyclic aromatic hydrocarbon (PAH) and polychlorinated biphenyl (PCB) emissions. The second area of work was directed at developing nondestructive infrared techniques in order to aid in the analysis of postage stamp adhesives. With Americans generating 150-200 million tons a year of Municipal Solid Waste (MSW) and disposing of nearly ninety percent of it in landfills, it is easy to understand why American landfills are approaching capacity. One alternative to landfilling is to process the MSW into RDF. There are technical and environmental problems associated with RDF. This work provides some answers concerning the amount of PAH and PCB emissions generated via the combustion of RDF with coal. It was found that the Ca(OH)2 binder greatly reduced both the PAH and the PCB emissions. In fact, PAH emissions at the ten-percent level were reduced more by using the binder than by the pollution control equipment. If the Ca(0H)2 binder can reduce not only PAH and PCB emissions, but also other noxious emissions, such as acid gases or dioxin, RDF technology could soon be the answer to the current landfill problems. The second portion of this work focused on developing a method to analyze stamp adhesives nondestructively. Using this method, it was fairly easy to differentiate among the three different types of adhesives that have been used by the United States Postal Service: gum arabic, dextrin, and polyvinyl alcohol. Differences caused by changes in chemicals added to the adhesives were also detected. Also, forgeries were detected with as much success, if not more, than by conventional methods. This work also led to the construction of equipment that allows large samples to be analyzed by reflectance infrared methods.
34

Poluentes Orgânicos Persistentes em sangue de aves marinhas no Arquipélago de São Pedro e São Paulo e na Ilha da Trindade / Persistent Organic Pollutants in blood of seabirds in the São Pedro and São Paulo Archipelago and Trindade Island

Silva, Daniela Alves Maia da 08 March 2019 (has links)
As aves marinhas são sensíveis às alterações em todos os níveis tróficos, decorrentes de variações na disponibilidade de presas e contaminação por alguns compostos, capazes de se acumular nos tecidos dos organismos e magnificar-se através da cadeia trófica. As ilhas oceânicas brasileiras abrigam importantes colônias reprodutivas de aves marinhas e, apesar de serem consideradas locais remotos, estão sujeitas à contaminação decorrente de atividades humanas. Este trabalho avaliou a presença de poluentes orgânicos persistentes (POPs) em sangue, uma matriz não-destrutiva, de seis espécies de aves marinhas no Arquipélago de São Pedro e São Paulo e na Ilha da Trindade, que possibilita o monitoramento destes indivíduos ao longo dos anos. Os resultados indicaram que os principais POPs detectados no sangue (em ng g-1 de massa úmida) foram PCBs (0,05 a 55,09), DDTs (0,01 a 17,36) e Mirex (0,01 a 5,53). A migração influenciou nos altos níveis de POPs encontrados em Pterodroma arminjoniana e a massa (g) média dos indivíduos apresentou uma forte correlação negativa com as concentrações dos compostos predominantes no sangue. O sexo das aves não contribuiu significativamente nas concentrações de POPs em espécies monotípicas, exceto para a espécie Sula leucogaster que apresenta dimorfismo sexual acentuado. O comportamento alimentar, avaliado através da análise de isótopos estáveis de carbono e de nitrogênio (δ13C e δ15N), bem como as condições biológicas de cada animal contribuíram para explicar as variações nos perfis de contaminação entre as diferentes espécies. No geral, observou-se que as concentrações de POPS nos dois locais apresentaram valores baixos e similares sugerindo a via atmosférica como principal mecanismo de entrada desses contaminantes para estas regiões. Os resultados inéditos de POPs em sangue das aves marinhas nas duas mais recentes unidades de conservação marinhas criadas no Brasil, podem contribuir como referência para o monitoramento desses compostos em longo-prazo nessas regiões. / Seabirds are sensitive to changes at all trophic levels, due to variations in prey availability and contamination by some compounds, which can be accumulated in the tissues of organisms and to be magnified through the trophic chain. The Brazilian oceanic islands harbor important seabird breeding colonies and, although they are considered remote sites, they are subject to contamination from human activities. This work evaluated the presence of Persistent Organic Pollutants (POPs) in blood, a non-destructive matrix, of six species of seabirds in the São Pedro and São Paulo Archipelago (SPSPA) and Trindade Island (TI), that allows the monitoring of these individuals over the years. The results indicated that the major POPs detected in blood (ng g-1 in wet weight) were PCBs (0.05 to 55.09), DDTs (0.01 to 17.36) and Mirex (0.01 to 5,53). Migration influenced the high levels of POPs found in Pterodroma arminjoniana and the mean mass (g) of the individuals drove a strong negative correlation with the concentrations of the predominant compounds in the blood. The gender of the individuals did not contribute significantly to the concentrations of POPs in monotypic species, except for the species Sula leucogaster that presents marked sexual dimorphism. The feeding behavior was evaluated through the analysis of stable isotopes of carbon and nitrogen (δ13C and δ15N) as well as the biological conditions of each animal contributed to explain the variations in the contamination profiles between the different species. In general, we observed that POPS concentrations at both sites presented low and similar values suggesting the atmospheric transport as the main input mechanism of these compounds for these regions. The unpublished results of POPs, in blood of seabirds from the two most recent marine conservation units created in Brazil, can contribute as reference values for their long-term monitoring in those regions.
35

Properties and analysis of dioxin-like compounds in marine samples from Sweden

Lundgren, Kjell January 2003 (has links)
Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (PCBs) have been assigned toxic equivalency factors (TEFs). These compounds are today routinely analysed with sophisticated analytical techniques. In a near future, there might be other dioxinlike compounds such as polychlorinated naphthalenes (PCNs), alkyl-polychlorodibenzofurans (R-PCDFs), and polychlorinated dibenzothiophenes (PCDTs) added to this list of toxic dioxin-like compounds. It is therefore important to have a readiness to analyse these new compounds in environmental samples. In this study, a multi-residue non-destructive analytical method for the analyses of these planar dioxin-like compound classes was developed. The use of HPLC PX-21 carbon column fractionation enabled the separation of interfering PCBs from coplanar PCBs and other planar dioxin-like compounds of interest. The obtained planar fraction containing the dioxin-like compounds was analysed using high-resolution GC-MS. Levels of PCNs in surface sediments and settling particulate matter in the northern Baltic Sea were determined. The concentrations of PCNs in background surface sediments were approximately 1 ng/g dw and the estimated PCN fluxes were similar to the pre-industrial levels determined in Europe. The PCN congener patterns in the surface sediments suggest that the PCNs deposited in the Baltic Sea originate from similar sources. Bioaccumulation of PCNs in a benthic food chain (sediment, amphipod, isopod, and four-horned sculpin) from the Gulf of Bothnia was studied. The results indicated that only a few PCN congeners biomagnified. The highest biomagnification factors (BMFs) were found for 2,3,6,7-substituted congeners and those lacking adjacent hydrogen-substituted carbon atoms. The calculated biota to sediment accumulation factors (BSAFs) showed that the tetra- and penta- CNs exhibited BSAF values higher than one, while BSAFs for the more chlorinated PCNs were less than one. A general difference between the northern and southern parts of the Gulf of Bothnia could be seen in the samples, with the lowest PCN and total PCB concentrations being found in the north and the highest in the south. This gradient is related to distance from the more industrialised and populated regions in the southern parts of Sweden and Finland, and central Europe. Analysis of R-PCDFs in crustacean samples from the Swedish west coast was performed using HRGC-MS/MS. The ΣR-PCDFs in these samples were present at concentrations up to 10 times higher than the ΣPCDFs. The relatively high concentrations of R-PCDFs in the crab samples demonstrate that these compounds bioaccumulate. The fate of a pollutant in the environment and the toxicity of a compound are governed by its physicochemical properties. The information found in a data set of properties can predict a compound’s mode of action. The following physicochemical properties for 87 PCDFs were measured: ultra-violetadsorption, relative retention times on two common gas chromatographic stationary phases, and relative mass spectrometric response factors using EI- and NCI- modes.
36

Sources of dioxins and other POPs to the marine environment : Identification and apportionment using pattern analysis and receptor modeling

Sundqvist, Kristina January 2009 (has links)
In the studies underlying this thesis, various source tracing techniques were applied to environmental samples from the Baltic region. Comprehensive sampling and analysis of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in surface sediments in Swedish coastal and offshore areas resulted in a unique data set for this region. Nearly 150 samples of surface sediments were analyzed for all tetra- to octa-chlorinated PCDD/Fs. The levels showed large spatial variability with hotspots in several coastal regions. Neither Sweden nor the EU has introduced guideline values for PCDD/Fs in sediment, but comparisons to available guidelines and quality standards from other countries indicate that large areas of primarily coastal sediments may constitute a risk to marine organisms. Multivariate pattern analysis techniques and receptor models, such as Principal Component Analysis (PCA) and Positive Matrix Factorization (PMF), were used to trace sources. These analyses suggested that three to six source types can explain most of the observed pattern variations found in the sediment samples. Atmospheric deposition was suggested as the most important source to offshore areas, thus confirming earlier estimates. However, spatial differences indicated a larger fraction of local/regional atmospheric sources, characterized by PCDFs, in the south. This was indicated by the identification of several patterns of atmospheric origin. In coastal areas, the influence of direct emission sources was larger, and among these, chlorophenol used for wood preservation and emissions from pulp/paper production and other wood related industry appeared to be most important. The historic emissions connected to processes involving chemical reactions with chlorine (e.g. pulp bleaching) were found to be of less importance except at some coastal sites. The analysis of PCDD/Fs in Baltic herring also revealed spatial variations in the levels and pollution patterns along the coast. The geographical match against areas with elevated sediment levels indicated that transfer from sediments via water to organisms was one possible explanation. Fugacity, a concept used to predict the net transport direction between environmental matrices, was used to explore the gas exchange of hexachlorocyclohexanes (HCHs) and polychlorinated biphenyls (PCBs) between air and water. These estimates suggested that, in the Kattegat Sea, the gaseous exchange of HCHs primarily resulted in net deposition while PCBs were net volatilized under certain environmental conditions. The study also indicated that, while the air concentrations of both PCBs and γ-HCH are mostly dependent upon the origin of the air mass, the fluctuations in α-HCH were primarily influenced by seasonal changes.
37

Piscivorous colonial waterbirds in the Columbia River estuary : demography, dietary contaminants, and management

Suzuki, Yasuko 13 January 2012 (has links)
Caspian terns (Hydroprogne caspia) and double-crested cormorants (Phalacrocorax auritus) nest in large colonies on East Sand Island in the Columbia River estuary, the largest known colonies for the two species in the world. Both species of piscivorous colonial waterbirds have been identified as predators with a significant impact on the survival of juvenile salmonids (Oncorhynchus spp.) listed under the U.S. Endangered Species Act. To better understand and address issues related to seabird-fisheries interactions in the Columbia River estuary, I conducted studies related to the ecology, conservation, and management of these two species of piscivorous waterbirds. I evaluated the demographics and inter-colony movements of Caspian terns belonging to the Pacific Coast metapopulation, with special emphasis on two breeding colonies, one on East Sand Island in the Columbia River estuary and the other on Crescent Island in the mid-Columbia River, based on re-sightings of color-banded individuals. Apparent annual adult survival at both colonies was high, and age at first reproduction was greater than previously reported for the species. Colony site philopatry of breeding adults at both colonies was high; however, some individuals prospected for breeding colonies over much of the Pacific Coast region and moved to other colonies over distances of up to 3,000 km. Some terns from the large colony in the Columbia River estuary responded quickly to the availability of new colony sites as distant as 550 km from the estuary, and established successful breeding colonies within less than a year of the new sites becoming available. The Caspian tern colony on East Sand Island appears to be an important source colony for a number of smaller, less productive colonies distributed over an extensive area from the Salton Sea, California to the Copper River Delta, Alaska, an area with limited and ephemeral nesting opportunities. Environmental contaminants have been a conservation concern for wildlife in the Columbia River estuary, especially species that consume fish and are therefore likely to bioaccumulate persistent organic pollutants. I measured and compared levels of polychlorinated biphenyls (PCBs) in eggs and chicks of Caspian terns and doublecrested cormorants, as well as their primary prey fish types, at colonies on East Sand Island and farther up-river. Based on differences in tern and cormorant diet composition at the various study colonies, higher PCB levels in eggs and chicks were associated with diets dominated by resident freshwater and estuarine fishes. PCB levels in prey fish were positively correlated with lipid content; however, PCB levels in the livers of chicks were negatively correlated with chick fat scores, suggesting that chick fat reserves are a sink for ingested PCBs. Lower PCB levels in terns and cormorants from East Sand Island compared to colonies farther up-river reflected diets with a higher proportion of marine forage fishes at East Sand Island; marine forage fishes had lower average levels of PCBs than their resident freshwater and estuarine counterparts. In order to explore non-destructive techniques for managing nesting colonies of double-crested cormorants, I evaluated habitat enhancement and social attraction, two techniques that have proven effective for relocating Caspian tern colonies to sites where impacts on fish stocks of conservation concern would be minimal. Cormorants were attracted to nest and successfully raised young at test plots on East Sand Island and on islands in the estuary with a previous history of cormorant nesting or unsuccessful nesting attempts. On an island with no history of cormorant nesting or prospecting, however, no cormorants were attracted to nest. My results suggest that attraction of nesting cormorants using these techniques is dependent on the previous history of cormorant nesting or nesting attempts, the frequency and intensity of disturbance by potential predators, and the presence of breeding cormorants nearby. While habitat enhancement and social attraction have potential as methods for redistributing nesting cormorants away from areas where fish stocks of concern are highly susceptible to predation, successful establishment of new colonies using these techniques will likely require a focus on sites with a history of cormorant nesting. Findings from this dissertation raise some concerns over the management of Caspian tern and double-crested cormorant colonies on East Sand Island in order to redistribute parts of these colonies to alternative sites and mitigate the impact of those piscivorous colonial waterbirds on ESA-listed salmonids. East Sand Island has supported source colonies of piscivorous colonial waterbirds for many smaller colonies throughout the region and is close to an abundant and relatively uncontaminated food supply. Also, alternative colony sites that can substitute for East Sand Island are not readily apparent, especially for double-crested cormorants. Therefore, management of Caspian tern and double-crested cormorant colonies on East Sand Island to benefit Columbia Basin salmonids needs to proceed cautiously and reversibly because of the implications for the region-wide populations of these piscivorous colonial waterbirds. / Graduation date: 2012

Page generated in 0.0965 seconds