• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 97
  • 93
  • 8
  • 8
  • 8
  • 8
  • 8
  • 4
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • Tagged with
  • 222
  • 222
  • 101
  • 101
  • 39
  • 31
  • 27
  • 26
  • 22
  • 22
  • 22
  • 17
  • 16
  • 15
  • 15
  • 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.
1

Integrating biochemical and growth responses in ecotoxicological assays with copepods

Dahl, Ulrika January 2008 (has links)
<p>The understanding of effects of chemical exposure in nature is lagging behind. Predictions of harmful effects of chemicals on aquatic organisms rely mainly on ecotoxicity tests. To improve the understanding of the biological linkage between the cellular and organismal responses to a chemical in an ecotoxicological test, the major aim of this doctoral thesis was to investigate the usefulness of two biochemical endpoints, contents of RNA and ecdysteroids, by incorporating them with life-history traits of copepods (Crustacea). To do so, the two methods needed to be established at our laboratory. Both biochemical methods are more commonly used in basic biological research, but I here present its usefulness in ecotoxicological testing. It was found that individual RNA content as a biochemical endpoint was significantly altered in the brackish water harpacticoid copepod Nitocra spinipes when exposed to the pesticide Lindane (paper IV) and low concentrations (0.16<g . L-1) of the pharmaceutical Simvastatin (paper I) during partial life cycle tests. However, the RNA content was insensitive as endpoint in the fresh water harpacticoid Attheyella crassa during multigenerational exposure (2 – 3 generations) to naturally contaminated sediments (paper III). The second biochemical endpoint, ecdysteroid content (a crustacean growth-hormone), was shown to be a useful tool for ecotoxicological studies using N. spinipes (paper IV), as well as for increasing the understanding of lipid turnover and reproduction of the marine calanoid copepod Calanus finmarchicus (paper V). In paper I and IV, I present a balanced ecotoxicological test, useful for substances with suspected developmental disruptive effects. In this type of test, a balance between test adequacy, exposure time, and costs has been proven useful. Further, the reliability of tests (paper II) with N. spinipes was increased by optimizing its food regime. In paper II, 25 different combinations of micro-algae were tested during short- and long time exposure, and a suitable food source (Rhodomonas salina) was identified, whilst poorer development and reproduction, malformations, and even mortality was induced by other algae. In conclusion, my studies provide useful tools for ecotoxicological testing, as well as for basic understanding of developmental biology of different copepod species.</p>
2

An in vitro study on the immunotoxicity of sewage effluents discharged into the Eerste River- Kuils River water catchment system.

Magcwebeba, Tandeka. January 2008 (has links)
<p>&quot / The aim of the study was to use in vitro human whole blood cultures to screen the water samples collected from the Eerste/Plankenbrug river system for cytotoxicity and inflammatory activity and for the first time investigate the impact on the cell- mediated and humoral immune pathways. Water samples were collected fronm the sites during the dry summer season and rainy winter season. Blood was collected from the healthy male volunteers and diluted with RPMI 1640. For cytotoxicity and inflammatory activity 2.5ul of blood for 18-20 hrs at 37 C... This study shows that waster from the Plankenbrug River is heavily polluted by contaminants from both the agricultural area and informal settlement of Kayamandi. These contaminants can be potentially immunotoxic during the summer season and they can result in inflammatory diarrheal disease and immunosuppression in exposed individuals...&quot / </p>
3

Integrating biochemical and growth responses in ecotoxicological assays with copepods

Dahl, Ulrika January 2008 (has links)
The understanding of effects of chemical exposure in nature is lagging behind. Predictions of harmful effects of chemicals on aquatic organisms rely mainly on ecotoxicity tests. To improve the understanding of the biological linkage between the cellular and organismal responses to a chemical in an ecotoxicological test, the major aim of this doctoral thesis was to investigate the usefulness of two biochemical endpoints, contents of RNA and ecdysteroids, by incorporating them with life-history traits of copepods (Crustacea). To do so, the two methods needed to be established at our laboratory. Both biochemical methods are more commonly used in basic biological research, but I here present its usefulness in ecotoxicological testing. It was found that individual RNA content as a biochemical endpoint was significantly altered in the brackish water harpacticoid copepod Nitocra spinipes when exposed to the pesticide Lindane (paper IV) and low concentrations (0.16&lt;g . L-1) of the pharmaceutical Simvastatin (paper I) during partial life cycle tests. However, the RNA content was insensitive as endpoint in the fresh water harpacticoid Attheyella crassa during multigenerational exposure (2 – 3 generations) to naturally contaminated sediments (paper III). The second biochemical endpoint, ecdysteroid content (a crustacean growth-hormone), was shown to be a useful tool for ecotoxicological studies using N. spinipes (paper IV), as well as for increasing the understanding of lipid turnover and reproduction of the marine calanoid copepod Calanus finmarchicus (paper V). In paper I and IV, I present a balanced ecotoxicological test, useful for substances with suspected developmental disruptive effects. In this type of test, a balance between test adequacy, exposure time, and costs has been proven useful. Further, the reliability of tests (paper II) with N. spinipes was increased by optimizing its food regime. In paper II, 25 different combinations of micro-algae were tested during short- and long time exposure, and a suitable food source (Rhodomonas salina) was identified, whilst poorer development and reproduction, malformations, and even mortality was induced by other algae. In conclusion, my studies provide useful tools for ecotoxicological testing, as well as for basic understanding of developmental biology of different copepod species.
4

Toxicity Assessment of PAHs and Metals to Bacteria and the Roles of Soil Bacteria in Phytoremediation of Petroleum Hydrocarbons

Wang, Wenxi 09 1900 (has links)
Petroleum hydrocarbons (PHCs) are a class of ubiquitous contaminants in the environment. PHCs impact to soil and water occur at well sites, refineries, service stations, and other facilities. Petroleum processing and consumption of petroleum products lead to the further release of other PHC pollutants such as Polycyclic Aromatic Hydrocarbons (PAHs) as well as metals. PHCs are causing serious environmental problems due to their widespread use. Hence, the central theme of this thesis addresses hydrocarbon pollutants and co-contaminating metals: their occurrence in environment, their mechanism of toxicity and their remediation via biological processes. This thesis is divided into two parts including seven chapters. The first part includes chapters 2, 3 and 4. Using bioluminescent bacterium Vibrio fischeri, a widely used bioindacator in environmental toxicology, the individual and mixture toxicities of phenanthrenequinone (PHQ), an oxyPAH, combined with copper and cadmium were assessed. PHQ is a main photoproduct of phenanthrene (PHE), a dominant PAH in the environment. Results showed that PHQ is much more toxic than its parent PAH. PHQ, alone or as mixtures with Cu and Cd, damages bacterial cells via enhancing production of reactive oxygen species (ROS). The mixture toxicity of Cu/PHQ was found to be dependent on the ratio of each chemical in the mixture. Two up-regulated genes, protein translocase subunit SecY gene and putative polysaccharide export protein YccZ precursor, were identified to be possibly response to PHQ exposure. Both genes are related to the detoxification of ROS. The second part of this thesis includes chapters 5, 6, and 7. Culture-dependent and -independent approaches were employed to evaluate the roles of bacteria as biodegraders or/and plant growth promoters during phytoremediation at a petroleum land farm (PLF) with a PHC concentration of ~130 g Kg-1. A plant growth promoting rhizobacteria (PGPR) enhanced phytoremediation system (PEP) was applied to remediate PLF soil. PEP promotes plant growth to establish dense vegetative cover. Results of both culturing and molecular methods showed that the enhanced populations and activities of soil microbes due to vigorous plant growth is a key factor in the success of PEP. Introduced PGPR could quickly establish significant populations by utilizing root exudates and dominate the PGPR population on seed coat and root surfaces at the early seedling stage of plant development, and thus modestly affected bacterial community structures at this time; thereafter, with plant growth, the effect of seed treatment on soil microbial community was masked by enhanced indigeneous microbial population. Therefore, the introduced PGPR did not exert significant influence on the indigenous microbial ecosystem. It does dramatically improve plant growth and PHC remediation. Thus, the PEP should be considered as an environmentally safe and effective approach for removing PHCs from impacted soils.
5

Toxicity Assessment of PAHs and Metals to Bacteria and the Roles of Soil Bacteria in Phytoremediation of Petroleum Hydrocarbons

Wang, Wenxi 09 1900 (has links)
Petroleum hydrocarbons (PHCs) are a class of ubiquitous contaminants in the environment. PHCs impact to soil and water occur at well sites, refineries, service stations, and other facilities. Petroleum processing and consumption of petroleum products lead to the further release of other PHC pollutants such as Polycyclic Aromatic Hydrocarbons (PAHs) as well as metals. PHCs are causing serious environmental problems due to their widespread use. Hence, the central theme of this thesis addresses hydrocarbon pollutants and co-contaminating metals: their occurrence in environment, their mechanism of toxicity and their remediation via biological processes. This thesis is divided into two parts including seven chapters. The first part includes chapters 2, 3 and 4. Using bioluminescent bacterium Vibrio fischeri, a widely used bioindacator in environmental toxicology, the individual and mixture toxicities of phenanthrenequinone (PHQ), an oxyPAH, combined with copper and cadmium were assessed. PHQ is a main photoproduct of phenanthrene (PHE), a dominant PAH in the environment. Results showed that PHQ is much more toxic than its parent PAH. PHQ, alone or as mixtures with Cu and Cd, damages bacterial cells via enhancing production of reactive oxygen species (ROS). The mixture toxicity of Cu/PHQ was found to be dependent on the ratio of each chemical in the mixture. Two up-regulated genes, protein translocase subunit SecY gene and putative polysaccharide export protein YccZ precursor, were identified to be possibly response to PHQ exposure. Both genes are related to the detoxification of ROS. The second part of this thesis includes chapters 5, 6, and 7. Culture-dependent and -independent approaches were employed to evaluate the roles of bacteria as biodegraders or/and plant growth promoters during phytoremediation at a petroleum land farm (PLF) with a PHC concentration of ~130 g Kg-1. A plant growth promoting rhizobacteria (PGPR) enhanced phytoremediation system (PEP) was applied to remediate PLF soil. PEP promotes plant growth to establish dense vegetative cover. Results of both culturing and molecular methods showed that the enhanced populations and activities of soil microbes due to vigorous plant growth is a key factor in the success of PEP. Introduced PGPR could quickly establish significant populations by utilizing root exudates and dominate the PGPR population on seed coat and root surfaces at the early seedling stage of plant development, and thus modestly affected bacterial community structures at this time; thereafter, with plant growth, the effect of seed treatment on soil microbial community was masked by enhanced indigeneous microbial population. Therefore, the introduced PGPR did not exert significant influence on the indigenous microbial ecosystem. It does dramatically improve plant growth and PHC remediation. Thus, the PEP should be considered as an environmentally safe and effective approach for removing PHCs from impacted soils.
6

An in vitro study on the immunotoxicity of sewage effluents discharged into the Eerste River- Kuils River water catchment system.

Magcwebeba, Tandeka. January 2008 (has links)
<p>&quot / The aim of the study was to use in vitro human whole blood cultures to screen the water samples collected from the Eerste/Plankenbrug river system for cytotoxicity and inflammatory activity and for the first time investigate the impact on the cell- mediated and humoral immune pathways. Water samples were collected fronm the sites during the dry summer season and rainy winter season. Blood was collected from the healthy male volunteers and diluted with RPMI 1640. For cytotoxicity and inflammatory activity 2.5ul of blood for 18-20 hrs at 37 C... This study shows that waster from the Plankenbrug River is heavily polluted by contaminants from both the agricultural area and informal settlement of Kayamandi. These contaminants can be potentially immunotoxic during the summer season and they can result in inflammatory diarrheal disease and immunosuppression in exposed individuals...&quot / </p>
7

Direct and indirect effects of an insecticide on Rana sphenocephala tadpoles /

Mills, Nathan E. January 2002 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.
8

Direct and indirect effects of an insecticide on Rana sphenocephala tadpoles

Mills, Nathan E. January 2002 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.
9

Ecological risk assessment of current-use pesticides in the Sixaola Watershed, Costa Rica /

Polidoro, Beth A. January 1900 (has links)
Thesis (Ph. D., Soil and Land Resources; with a concentration in Biodiversity Conservation and Agroforestry)--University of Idaho and Centro Agronómico Tropical de Investigación y Enseñanza, August 2007. / Major professors: Matthew J. Morra and Eduardo Somarriba. Includes bibliographical references. Also available online (PDF file) by subscription or by purchasing the individual file.
10

The influence of environmental exposures across the life course on patterns of disease : environmental equity and public health in England and Wales

Wheeler, Benedict William January 2002 (has links)
No description available.

Page generated in 0.1248 seconds