• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 99
  • 54
  • 26
  • 26
  • 18
  • 7
  • 3
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 266
  • 86
  • 54
  • 38
  • 30
  • 27
  • 27
  • 26
  • 25
  • 24
  • 22
  • 22
  • 22
  • 21
  • 19
  • 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.
81

Spatial and Geochemical Techniques to Improve Exposure Assessment of Manganese in Windsor, Ontario

Nugent Ayres, Michelle V. 29 September 2011 (has links)
This study was conducted to investigate the urban geochemistry of the city of Windsor (Ontario) and to provide added source apportionment information to work being carried out by the Canadian government. The goal of this study was to investigate the distribution, spatial variation and sources of manganese in urban Windsor soil. The literature indicates that human exposure to high levels of manganese, via inhalation, can cause respiratory and/or neurological effects. At the outset of the present study it was first hypothesized that vehicular traffic was the dominant source of anthropogenic manganese. An alternative hypothesis was that there were multiple anthropogenic sources of manganese in Windsor. The sample collection scheme was designed to determine (1) the current and background soil concentrations of manganese in Windsor, (2) the spatial distribution of manganese in order to reveal sources of manganese, and (3) the manganese content of moss-sequestered airborne particles, which can potentially deposit onto the soil surface, using low-technology biomonitoring. The first phase of the study consisted of a preliminary soil survey which identified elevated areas of soil manganese concentrations. During this survey, the field efficiency of a field portable X-ray fluorescence (FPXRF) instrument, as well as sample preparation methods were evaluated. Efficiency of the FPXRF was determined by comparison to ICP-MS, a traditional trace element analysis method. The preliminary soil survey identified several areas of elevated (ranging from 884 to 2390 ppm) soil manganese which were further investigated during the second, more complete, soil survey. The moss biomonitoring technique of using moss bags was used to collect airborne particles for semi-quantitative analysis. Analysis of soil samples included total manganese and other trace elements, pH, moisture and carbon content, and manganese speciation. Urban Windsor soil manganese distribution revealed both natural and anthropogenic sources of soil manganese and three distinct soil sample types, transect, baseline and natural. In general, manganese in Windsor had a west-to-east trend of decreasing levels in soil and moss-sequestered airborne particles. The latter showed a modern-day elemental signature while the former (collocated soil) a legacy elemental signature. It was concluded that both the FPXRF instrument and the moss biomonitoring technique can be useful screening tools in studies of urban environments.
82

Lecanora muralis: eine epilithische Krustenflechte als Biomonitor für luftgetragene Spurenmetalle

Lambrecht, Susanne 10 July 2009 (has links) (PDF)
In der vorliegenden Dissertation wurde die Eignung von Flechten als Biomonitor für die retrospektive Ermittlung der Luftqualität im Hinblick auf Spurenstoffe systematisch untersucht. Dazu wurde die ubiquitär verbreitete Krustenflechte Lecanora muralis ausgewählt und mit ihrer Hilfe der Einfluss von Lokalität, Probennahmehöhe und -position, Sammelmethodik, Präparationsmethodik, Wachstum etc. eingehend bearbeitet. Die Luftqualität in Nordrhein-Westfalen galt es als regionales Beispiel mit hochdifferenzierten Einflüssen zu charakterisieren. Hierfür wurden Flechten an ihren natürlichen Standorten gesammelt und auf die folgenden Elementgehalte analysiert (sog. passives Biomonitoring): Ag, As, Ba, Ce, Cd, Cu, Fe, Mn, Ni, Pb, Se, Sn, Tl, V und Zn.
83

Phthalates: Science, Advocacy, and Biomonitoring

Mitten, Lauren 01 January 2015 (has links)
Phthalates are a class of ubiquitous environmental contaminants that cause health problems including reproductive disorders, asthma, and obesity. Advocacy against phthalates has been taking place in the US since the mid-1990s, and eight in-depth interviews were conducted with advocates and scientists in order to construct a history of this advocacy. There have been a variety of campaigns and victories; those around medical devices, children’s products, and personal care products are examined in detail. Phthalate exposure data for a representative sample of the US population indicates that exposure to DEP, DEHP, DnBP, and BBzP went down between 1999 and 2010. As these were the phthalates that had the largest volume of advocacy during the period researched, this decrease suggests that advocacy around specific phthalates is effective in reducing exposure and that more advocacy around phthalates, and potentially other harmful chemicals, could result in further decreased exposure and improved health in the US population. Additional research using more finely graded biomonitoring data would help deepen understanding about correlations between advocacy and phthalate exposure. In reviewing the health effects of phthalates, it was found that a disproportionate amount of the research is on male reproductive health effects, which is partially responsible for the fact that a disproportionate amount of phthalate advocacy is on heath effects relating to men, particularly male babies. Both phthalate science and advocacy sometimes treat women instrumentally, objectifying them or regarding them as incubators. To combat this, scientists could do more research on the health effects of phthalates on women and advocates could take more care not to neglect or instrumentalize women in their efforts to reduce phthalate exposure for all people.
84

Towards the successful application of diatom-based biomonitoring in South Africa / Jonathan Charles Taylor

Taylor, Jonathan Charles January 2006 (has links)
Water is a scarce and precious resource in South Africa. Not only is the quality and quantity of water available limited by climatic conditions but these resources are often impacted by domestic and industrial effluents, as well as run-off from agriculture. Monitoring the aquatic environment helps to determine the impact of various pollutants. Chemical monitoring, important as it is, can only at best give a "snapshot" of water quality at a particular moment in time. Biomonitoring in particular forms a vital part of monitoring programmes as it gives a time integrated reflection of a particular pollutant or group of pollutants on the ecosystem. Although diatoms have long been studied in South Africa, as well as being used in the past to indicate water quality, the current suite of bioindicator organisms used in this country has not until recently included diatoms, or any autotrophic organisms for that matter. This body of work is presented with the aim of facilitating the use of diatoms as bioindicators of water quality in South Africa. Methods for the collection, preparation and analysis of diatoms have been collated and standardized. A number of European and other indices have been tested in diverse localities for use in indicating recent and historical water quality. The impact of diffuse mine effluent on diatom community structure has also been discussed. A new species common in impacted waters (i.e. a potential indicator species for these conditions) has been described and a guide to the common diatoms of South Africa is presented which, it is hoped, will be of use to those who wish to commence with a study of South Africa's diatom flora. The results of this study show that diatom indices are successful in reflecting both current and past water quality in South Africa. This result justifies the inclusion of diatoms with the current suite of bioindicator organisms as well as in national monitoring initiatives such as the River Health Programme. Concluding comments underline the importance of using diatoms as indicators, not only of water quality, but also as indicators of aquatic microorganism biodiversity, or loss thereof. The need for continued research in the fields of diatom ecology and taxonomy is also highlighted. / Thesis (Ph.D. (Environmental Science))--North-West University, Potchefstroom Campus, 2007.
85

The use of diatoms to indicate water quality in wetlands : A South African perspective / by Malebo D. Matlala

Matlala, Malebo Desnet January 2010 (has links)
In a semi-arid country like South Africa, the availability and quality of water has always played an important part in determining not only where people can live, but also their quality of life. The supply of water is also becoming a restriction to the socio-economic development of the country, in terms of both the quality and quantity of what is available. Thus different monitoring techniques should be put in place to help inform the process of conserving this precious commodity and to improve the quality of what is already available. Water quality monitoring has traditionally been by the means of physico-chemical analysis; this has more recently been augmented with the use of biomonitoring techniques. However, since the biota commonly used to indicate aquatic conditions are not always present in wetlands; this study tested the use of diatoms as bio-indicators in wetlands. Diatom samples were collected from thirteen wetlands in the Western Cape Province, and cells from these communities were enumerated and diatom ?based indices were calculated using version 3.1 of OMNIDIA. These indices were useful for indicating water quality conditions when compared to the measured physico-chemical parameters. In addition, most diatom species found were common to those found in riverine environments, making the transfer of ecological optima possible. The objective of the study was to provide a preliminary diatom-based index for wetlands, however, given the relatively small study area and the strong bias towards coastal wetlands it was deemed inadvisable to construct such an index, instead several indices are recommended for interim use until further research that more comprehensively covers wetlands in South Africa has been conducted. It is thus the recommendation of this study that more data is collected for comparison to other wetlands and that in the interim, indices such as SPI be applied for routine biomonitoring of these environments. / Thesis (M.Sc. (Botany))--North-West University, Potchefstroom Campus, 2010.
86

Triclosan: Source Attribution, Urinary Metabolite Levels and Temporal Variability in Exposure Among Pregnant Women in Canada

Weiss, Lorelle D. 10 October 2013 (has links)
OBJECTIVE: To measure urinary triclosan levels and their variability across pregnancy, and to identify sources of triclosan exposure among Canadian pregnant women. METHODS: Single spot and serial urine samples, as well as consumer product use information were collected across pregnancy and post-partum from 80 healthy pregnant women in Ottawa. Analyses included descriptives, linear mixed effects and parametric trend modeling, and surrogate category analysis. RESULTS: Triclosan was detected in 87% of maternal urine samples (LOD=3.0 µg/L). Triclosan concentrations varied by time of day of urine collection (p=0.0006), season of sampling (p=0.019), and parity (p=0.038). Triclosan was included in 4% of all personal care products used by participants; 89% of these triclosan products were varying brands of toothpaste and hand soaps. CONCLUSION: This study provided the first data on temporal variability urinary triclosan levels, and on source attribution data in Canadian pregnant women. Results will assist with population-specific exposure assessment strategies.
87

Towards the successful application of diatom-based biomonitoring in South Africa / Jonathan Charles Taylor

Taylor, Jonathan Charles January 2006 (has links)
Water is a scarce and precious resource in South Africa. Not only is the quality and quantity of water available limited by climatic conditions but these resources are often impacted by domestic and industrial effluents, as well as run-off from agriculture. Monitoring the aquatic environment helps to determine the impact of various pollutants. Chemical monitoring, important as it is, can only at best give a "snapshot" of water quality at a particular moment in time. Biomonitoring in particular forms a vital part of monitoring programmes as it gives a time integrated reflection of a particular pollutant or group of pollutants on the ecosystem. Although diatoms have long been studied in South Africa, as well as being used in the past to indicate water quality, the current suite of bioindicator organisms used in this country has not until recently included diatoms, or any autotrophic organisms for that matter. This body of work is presented with the aim of facilitating the use of diatoms as bioindicators of water quality in South Africa. Methods for the collection, preparation and analysis of diatoms have been collated and standardized. A number of European and other indices have been tested in diverse localities for use in indicating recent and historical water quality. The impact of diffuse mine effluent on diatom community structure has also been discussed. A new species common in impacted waters (i.e. a potential indicator species for these conditions) has been described and a guide to the common diatoms of South Africa is presented which, it is hoped, will be of use to those who wish to commence with a study of South Africa's diatom flora. The results of this study show that diatom indices are successful in reflecting both current and past water quality in South Africa. This result justifies the inclusion of diatoms with the current suite of bioindicator organisms as well as in national monitoring initiatives such as the River Health Programme. Concluding comments underline the importance of using diatoms as indicators, not only of water quality, but also as indicators of aquatic microorganism biodiversity, or loss thereof. The need for continued research in the fields of diatom ecology and taxonomy is also highlighted. / Thesis (Ph.D. (Environmental Science))--North-West University, Potchefstroom Campus, 2007.
88

The use of diatoms to indicate water quality in wetlands : A South African perspective / by Malebo D. Matlala

Matlala, Malebo Desnet January 2010 (has links)
In a semi-arid country like South Africa, the availability and quality of water has always played an important part in determining not only where people can live, but also their quality of life. The supply of water is also becoming a restriction to the socio-economic development of the country, in terms of both the quality and quantity of what is available. Thus different monitoring techniques should be put in place to help inform the process of conserving this precious commodity and to improve the quality of what is already available. Water quality monitoring has traditionally been by the means of physico-chemical analysis; this has more recently been augmented with the use of biomonitoring techniques. However, since the biota commonly used to indicate aquatic conditions are not always present in wetlands; this study tested the use of diatoms as bio-indicators in wetlands. Diatom samples were collected from thirteen wetlands in the Western Cape Province, and cells from these communities were enumerated and diatom ?based indices were calculated using version 3.1 of OMNIDIA. These indices were useful for indicating water quality conditions when compared to the measured physico-chemical parameters. In addition, most diatom species found were common to those found in riverine environments, making the transfer of ecological optima possible. The objective of the study was to provide a preliminary diatom-based index for wetlands, however, given the relatively small study area and the strong bias towards coastal wetlands it was deemed inadvisable to construct such an index, instead several indices are recommended for interim use until further research that more comprehensively covers wetlands in South Africa has been conducted. It is thus the recommendation of this study that more data is collected for comparison to other wetlands and that in the interim, indices such as SPI be applied for routine biomonitoring of these environments. / Thesis (M.Sc. (Botany))--North-West University, Potchefstroom Campus, 2010.
89

Spatial and Geochemical Techniques to Improve Exposure Assessment of Manganese in Windsor, Ontario

Nugent Ayres, Michelle V. 29 September 2011 (has links)
This study was conducted to investigate the urban geochemistry of the city of Windsor (Ontario) and to provide added source apportionment information to work being carried out by the Canadian government. The goal of this study was to investigate the distribution, spatial variation and sources of manganese in urban Windsor soil. The literature indicates that human exposure to high levels of manganese, via inhalation, can cause respiratory and/or neurological effects. At the outset of the present study it was first hypothesized that vehicular traffic was the dominant source of anthropogenic manganese. An alternative hypothesis was that there were multiple anthropogenic sources of manganese in Windsor. The sample collection scheme was designed to determine (1) the current and background soil concentrations of manganese in Windsor, (2) the spatial distribution of manganese in order to reveal sources of manganese, and (3) the manganese content of moss-sequestered airborne particles, which can potentially deposit onto the soil surface, using low-technology biomonitoring. The first phase of the study consisted of a preliminary soil survey which identified elevated areas of soil manganese concentrations. During this survey, the field efficiency of a field portable X-ray fluorescence (FPXRF) instrument, as well as sample preparation methods were evaluated. Efficiency of the FPXRF was determined by comparison to ICP-MS, a traditional trace element analysis method. The preliminary soil survey identified several areas of elevated (ranging from 884 to 2390 ppm) soil manganese which were further investigated during the second, more complete, soil survey. The moss biomonitoring technique of using moss bags was used to collect airborne particles for semi-quantitative analysis. Analysis of soil samples included total manganese and other trace elements, pH, moisture and carbon content, and manganese speciation. Urban Windsor soil manganese distribution revealed both natural and anthropogenic sources of soil manganese and three distinct soil sample types, transect, baseline and natural. In general, manganese in Windsor had a west-to-east trend of decreasing levels in soil and moss-sequestered airborne particles. The latter showed a modern-day elemental signature while the former (collocated soil) a legacy elemental signature. It was concluded that both the FPXRF instrument and the moss biomonitoring technique can be useful screening tools in studies of urban environments.
90

Characterization of Polycyclic Aromatic Hydrocarbons (PAH) in airborne particles and assessment of human exposure to PAHs

Li, Zheng 31 March 2009 (has links)
Polycyclic aromatic hydrocarbons (PAHs) are a group of toxic air pollutants formed during incomplete combustion and are ubiquitously distributed in the environment. To determine particle-bound PAHs in archived PM2.5 samples taken with low flow rate in Atlanta, a sensitive and robust method was developed for measuring 28 PAHs and methyl PAHs in PM samples using isotope dilution gas chromatography/high resolution mass spectrometry (GC/HRMS). The method was then used to analyze PM2.5 samples collected at three sites (rural, urban, suburban-highway) from the Assessment of Spatial Aerosol Composition in Atlanta (ASACA) network. Distinct seasonal and spatial variations were observed in PAH concentration. Particle-bound PAH levels were significantly higher in winter than in summer. The suburban-highway site had higher PM2.5-bound PAH concentration than did the urban site, and the rural site had the lowest PAH levels. Retene, a proposed biomass burning tracer, captured both the high leaves-grasses-bushes-branches burning season and the high wood burning months, suggesting that it might be a better marker for all biomass burning, while potassium ion might be a more specific tracer for wood burning. Human exposure to PAHs can be assessed by characterizing their hydroxy PAH (OH-PAH) metabolites in urine samples. A method was developed to measure 24 urinary OH-PAHs, metabolites of 8 parent PAHs, using enzymatic de-conjugation, automatic liquid-liquid extraction, and GC/HRMS. A study was then carried out to evaluating the variability of the urinary biomarker levels in a non-occupationally exposed non-smoking reference group. Levels of urinary PAH metabolites varied widely both within-subject and between-subjects and the within-day variance far exceeded the between-day variance. There were also considerable temporal correlations for these biomarkers. Sample size calculations were conducted and taking 24-hour voids would require the least number of subjects, which should be considered during epidemiological study design. Finally, a study was conducted to evaluate exposure to ambient PAHs in an urban setting among 8 non-occupationally exposed non-smoking volunteers employing both personal air sampling and urine biomonitoring. PAH levels varied largely in air samples taken at home, at work, and while driving or jogging. Monitoring urinary OH-PAH levels can capture both inhalation and dietary exposures. Total inhaled PAH was correlated with total excreted OH-PAHs, suggesting that by combining personal air sampling and biomonitoring, exposure to environmental PAHs can be well characterized even for low-level exposure.

Page generated in 0.0922 seconds