No description available.

Cryptophlebia leucotreta granulovirus (CrleGV-SA) is a baculovirus specifically pathogenic to the citrus pest false codling moth, Thaumatotibia leucotreta. CrleGV- SA is formulated as a commercial biopesticide, Cryptogran® (River Bioscience, South Africa). The virus has a stable, proteinaceous crystalline occlusion body (OB) that protects the nucleocapsid. The major limitation to the use of baculoviruses is their susceptibility to the ultraviolet (UV) component of sunlight, which rapidly and greatly reduces their efficacy as biopesticides. The UVA and UVB components are the most destructive to biological organisms. To date no publication has reported the effect of UV on the structure and virulence of CrleGV, or the effectiveness of the OB as a UV protectant. In this study the effect of UV irradiation on the structure and infectivity of pure CrleGV-SA and Cryptogran® was investigated using scanning electron microscopy (SEM), Raman spectroscopy, qPCR, and bioassays. The project included laboratory and field studies. In the laboratory, CrleGV-SA and Cryptogran® were exposed to either UVA or UVB for periods of 24 hours to 7 days before analysis. In the field, Cryptogran® was applied to trees in a citrus orchard with young fruit. The fruit were collected from 24 hours to 28 days after application and bioassays conducted to assess the effect of sunlight over time on virus structure and efficacy when applied to the northern or southern sides of the trees. No surface morphological changes to the virus were detected using SEM. However, small compositional changes were detected by Raman spectroscopy. qPCR and bioassays demonstrated that UV irradiation damaged the viral DNA, greatly reducing the infectivity of pure CrleGV-SA and Cryptogran®. Exposure to UVB reduced the virulence of the virus more than UVA. The field studies revealed that the activity of CrleGV-SA decreased more on the northern side of the trees than on the southern side.

Exposure of the skin to ultraviolet radiation (UVR) results clinically in the formation of deep wrinkles and mottled pigmentation and histologically, in a vast remodelling of the dermal extracellular matrix (ECM), in particular the elastic fibre network. Fibrillin microfibrils and fibulin-5 are early biomarkers of photoageing, where a loss of these fibres from the dermal epidermal junction is apparent. A study by our group showed that isolated fibrillin microfibrils and fibronectin which are rich in amino acids which absorb energy from UVR (UV-chromophores) are susceptible to UVR-induced damage, whilst UV-chromophore poor collagen type I is not. This research, with other earlier studies, indicates that acellular mechanism may work in tandem with cell-mediated up-regulation of matrix metalloproteinases (MMPs) in the progression of photoageing. This thesis aims to: i) test whether acellular mechanisms of photoageing are a result of direct photon absorption and/or the photodynamic production of reactive oxygen species (ROS); ii) assess the functional consequences of UVB degradation on the susceptibility of fibrillin microfibrils to MMPs and; iii) assay whether ECM proteins are differentially susceptible to solar simulated radiation (SSR) or UVA (315-400nm) alone using physiologically relevant doses of irradiation. Isolated proteins were exposed to UVB (280-315nm) in depleted-O2 conditions and in the presence of deuterium oxide. Depleted-O2 conditions decreased and deuterium oxide conditions increased UVR-induced degradation. Isolated proteins also show a similar pattern of degradation when exposed to H2O2 as an exogenous source of ROS. These results indicate that ROS play an important role in the differential degradation of dermal proteins. MMPs-3 and -9 are both upregulated in the skin after exposure to UVR and have the ability to degrade elastic fibre components. After exposure to UVB, damaged fibrillin microfibrils become more susceptible to degradation by both MMPs-3 and -9. Chromophore-rich fibrillin microfibrils and fibronectin are susceptible to degradation by both SSR and UVA alone, whereas chromophore-poor collagens type I and VI and tropoelastin are not. These results support our previous findings that amino acid composition of proteins is a good indicator of their relative susceptibility to UV-induced damage with a physiologically relevant irradiation system. In conclusion this work shows that ROS are an important mediator of acellular mechanisms of photoageing and that amino acid composition is a good indication of relative susceptibility of proteins to both ROS and UVR. The ability to predict ROS-susceptible proteins also has wider implications for human ageing as a whole.

Please read the abstract in the section, 00front, of this document / Dissertation (MEng)--University of Pretoria, 2008. / Chemical Engineering / unrestricted

Alpine zooplankton are exposed to a variety of stressors in their natural environment including ultraviolet radiation. Physiological coping mechanisms such as the accumulation of photoprotective compounds provide these zooplankton protection from many of these stressors. Elevated levels of carotenoid compounds such as astaxanthin have been shown to help zooplankton survive longer when exposed to ultraviolet radiation presumably due to the strong antioxidant properties of carotenoid compounds. This antioxidant capacity is important because it may ameliorate natural and anthropogenic stressor-induced oxidative stress. While previous researchers have shown carotenoid compounds impart increased resistance to ultraviolet radiation in populations of zooplankton, little work has focused on the toxicological implications of PAH induced phototoxicity on zooplankton containing high levels of carotenoid compounds. This thesis discusses research studying the role that carotenoid compounds play in reducing PAH induced phototoxicity. By sampling different lakes at elevations ranging from 9,500' to 12,700' in the front range of the Colorado Rocky Mountains, copepod populations containing different levels of carotenoid compounds were obtained. These populations were then challenged with fluoranthene and ultraviolet radiation. Results discussed include differences in survival and levels of lipid peroxidation among populations exhibiting different levels of carotenoid compounds, and the toxicological and ecological implications of these results.

Published Article / Alicyclobacillus acidoterrestris is a non-pathogenic, spore-forming bacterium that can survive the commercial pasteurisation processes commonly used during fruit juice production. Surviving bacterial endospores germinate, grow and cause spoilage of high acid food products. Fruit juices can be treated using ultraviolet light (UV-C) with a wavelength of 254 nm, which has a germicidal effect against micro-organisms. In this study, A. acidoterrestris was inoculated into water, used wash water from a fruit processing plant and grape juice concentrate. Ultraviolet dosage levels (J L-1) of 0, 61, 122, 183, 244, 305 and 367 J L-1 were applied using a novel UV-C turbulent flow system. The UV treatment method was shown to reliably achieve in excess of a 4 log10 reduction (99.99%) per 0.5 kJ L-1 of UV-C dosage in all the liquids inoculated with A. acidoterrestris. The applied novel UV technology could serve as an alternative to thermal treatments of fruit juices for the inactivation of Alicyclobacillus spores as well as in the treatment of contaminated wash water used in fruit processing.

No description available.

Protection against the harmful effects of ultraviolet radiation is of increasing importance due to the depletion of stratospheric ozone, which shields the earth from harmful UVC rays (in the range 200-280 nm) and some UVB rays (in the range 280-290 nm). In addition, as the skin is repeatedly exposed to solar radiation, the possibility exists that the incidence of skin cancer is enhanced. This has led to the increased use of commercial sunscreens, which apart from their benefits, also have undesirable effects such as photodegradation and skin penetration. We therefore studied the photodegradation of two sunscreen absorbers that are used in most sunscreen formulations. The combination of the UVB filter, 2-ethylhexyl-p-methoxycinnamate (EHMC), and the UVA filter, avobenzone (AVO), are commonly used in sunscreen products. These two filters are known to exhibit differing photostabilities in different media. The aim of this project was to investigate their photochemical behaviour in a polar and a non-polar solvent and to identify the UV-induced breakdown products. Methanol was chosen as the polar medium and cyclohexane as the non-polar medium. The sunscreen filters were irradiated either singly or in combination in the two solvents with wavelengths greater than 300 nm. The irradiated samples were analysed by UV-spectrophotometry, high performance liquid chromatography (HPLC) and gas chromatography (GC). The effects of direct irradiation with UVB and UVA light, quenchers and photosensitisers were also examined. EHMC is supplied commercially as the trans-isomer and upon irradiation photoisomerises, in both methanol and cyclohexane, to its cis-isomer. AVO is photostable in methanol but photodegrades in cyclohexane. This behaviour is also evident when mixtures of the two filters are irradiated. The loss in absorbance of both EHMC and AVO was monitored by UV-spectrophotometric analysis. Since EHMC does not absorb UV light at the wavelength of maximum absorbance of AVO, a method to quantify the amount of EHMC and AVO present in the mixture was devised. In order to identify the degradation products, HPLC and GC techniques were implemented. The photoproducts formed in the polar methanolic medium were separated and quantified by HPLC analysis. Gas chromatography with flame ionisation detection (GC-FID) was used to separate the photoproducts formed in the non-polar cyclohexane medium. Gas chromatography with mass-spectral detection (GC-MS) was used to identify the photoproducts formed upon irradiation of AVO and to show that UVA irradiation of AVO photosensitises the isomerisation of EHMC. The rate of a photochemical reaction depends upon a number of factors including the number of photons absorbed by sunscreen absorbers. Chemical actinometry was used to determine the number of photons absorbed by EHMC, AVO and the mixture of the two in methanol and cyclohexane. The number of photons absorbed by AVO in cyclohexane was used to determine the quantum yield for the photodegradation of AVO. We also determined the rate constants for EHMC photoisomerisation and AVO photodegradation. Finally, we investigated the effect of sunlight on commercial sunscreens containing EHMC and AVO. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

The ionization and thermal balances are considered for a gas that is ionized by a dilute radiation field, taking into account the diffuse ionizing radiation produced by the gas. A number of models are constructed in which the electron temperature and the ionization of the elements H, He, C, N, 0, Ne, and Mg are determined for optically thin and optically thick gases ionized by ultraviolet synchrotron radiation under different conditions. Conclusions are then drawn about the general characteristics of ionization by synchrotron radiation. It is shown that, in an optically thin gas, because of the insensitive frequency- dependence of synchrotron radiation each element occupies a number of different stages of ionization at any one point in the gas. It is also shown that in an optically thick gas the heavy elements remain ionized to much greater distances from the source than hydrogen and helium, and that the gas becomes thermally unstable when H and He have become almost completely neutral. In addition, observations of the emission -line intensities of the Crab Nebula are compared with a model of this object. Considerable disagreement exists between the observed and predicted intensities, and possible reasons for the discrepancy are discussed.

Intermittent sun exposure and sun sensitivity factors are the most well described risk factors for the development of cutaneous melanoma (CM). Other potential environmental risks for CM, such as arsenic, are rarely examined. Total sun exposure has not been a consistent risk factor for CM, but recall bias in self-reporting sun exposure throughout life may limit the ability to detect a true association. Objective measures of sun exposure including remotely sensed ambient ultra-violet radiation (UVR) may allow for better capture of total sun exposure. In three chapters, spatially derived factors (ambient UVR, environmental soil arsenic, drinking water arsenic) were observed to determine their relevance in exposure assessment and subsequent risk for CM.UVR trends were investigated using available satellite data (1978-2014) to generate inferences for UVB changes over time in the United States. We found that UVB changed across the study area, but these changes lack biological relevance based on the magnitude of changes observed. Thus, a more objective measure of lifetime ambient sun exposure may be estimated using 30-year average UVR by month in future studies. The spatial correlation between environmental soil arsenic and drinking water across the state of Iowa was investigated. Arsenic concentrations in soil were not significantly spatially correlated with either municipal public water source or non-municipal water source arsenic concentrations. Based on these findings, soil arsenic may not serve as a valid surrogate marker for arsenic in drinking water.In Chapter 5, we assessed the relationship of spatially derived estimates of lifetime ambient UVR, environmental arsenic exposure from soil and drinking water, and CM in a population-based case-control study. Our findings suggest that total sun exposure is positively associated with CM, while arsenic concentration in environmental soil and drinking water were not associated. Sun exposure measured through ambient UVR exposure may allow for better understanding of the association between cumulative or total sun exposure and CM. Additionally, more studies need to be completed to estimate the potential risks for CM in regions where high arsenic concentrations may not be endemic.