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.

No description available.

Lasers pose a safety hazards both to skin and particularly to something you value highly - your vision. The increasingly widespread use of IR wavelengths laser systems requires awareness with the potential hazards associated with the misuse of these valuable products. The principal goal of this research is to integrate experimental and theoretical descriptions of thermal response of skin and cornea to IR wavelength laser irradiation to yield a basis for the dosimetry of laser-tissue interaction. The threshold radiant exposures for various spot sizes and exposure durations were investigated on in vivo skin and cornea for 2.0 [mu]m laser irradiation. Similar study was also conducted on in vivo skin using 1.214 [mu]m laser and compared with 2.0 [mu]m results. This PhD study has, for the first time, linked temperature response, histopathology, and the more common "minimal visible lesion (MVL)" endpoint into what can be a meaningful comparison of rate process models for injury. Based on experimental data, a finite-element optical-thermal-damage model was developed. Histological damage was measured and modeled using sub-threshold, threshold, and super-threshold 2.0 [mu]m laser powers. The data provided experimental evidence of the correlation of sub-threshold histological change to visible threshold lesion for the irradiation condition of this study. Moreover, the computer model, supported by experimental validation, ensured that rate process models were used correctly in the prediction of "MVL" thresholds which were based upon a finite damage extent and not necessarily central surface layer damage. Thermal image method was employed to measure the absorption coefficient of in vivo skin at 2.0 [mu]m, at which wavelength scattering can be ignored. At laser wavelengths below 1.4 [mu]m where scattering cannot be ignored, an ameliorative method was explored to measure absorption and reduce scattering of in vivo tissue by combining pulse photothermal radiometry (PPTR) and diffuse reflectance (DR) measurements.

Stratospheric ozone plays an important role in absorbing ultraviolet radiation. The well-known depletion of the ozone layer has raised several concerns in terms of an expected increase in surface ultraviolet radiation. South Africa, situated in the southern mid-latitude regions, has experienced a general downward trend in total column ozone since 1979, As a result of this negative trend in total column ozone, the ultraviolet flux at the earth's surface is expected to increase. Excessive exposure to ultraviolet radiation is known to have acute and chronic effects on human health, including erythema and skin cancer. Numerous studies have acknowledged a relationship between childhood ultraviolet radiation exposure and the risk of contracting skin cancer, namely malignant melanoma, during adulthood. The aim of this study is to investigate the ultraviolet radiation dose and exposure of children and adolescents in Durban, South Africa. Polysulphone film badges were used to quantify the daily erythemal ultraviolet radiation dose of 30 individuals of varying ages and skin types, engaged in different activities, over a one-week period during summer. The results highlight the diversity of childrens' and adolescents' behavioural patterns, with behaviour being found to play an important role in determining an individual's ultraviolet radiation dose. The mean daily erythemal ultraviolet radiation dose of the children and adolescents was 1.03 MED units with a median of 0.57 MED units and a 95% range of 0.22 - 7.22 MED units. The most striking finding was that the median value was below the critical value of 1 MED unit. An explanation for the unexpectedly low erythemal ultraviolet radiation doses recorded in this study was sought in the prevailing climatic conditions. Ambient erythemal ultraviolet radiation levels recorded during the study period were high, ranging between 20.57 - 30.60 MED units. However, high temperatures (>27°C), coupled with high humidity values, may have encouraged the children and adolescents to avoid direct sunlight and find shade while outdoors. The daily erythemal ultraviolet radiation doses of the children and adolescents were also compared to the ambient erythemal ultraviolet radiation levels received on a horizontal surface by a YES UVB-l pyranometer located at the University of Natal (Durban). Children and adolescents in Durban received approximately 4.58% of the total daily ambient erythemal ultraviolet radiation incident upon a horizontal surface. This was found to be similar to a study (5 - 6%) conducted by Diffey et al. (1996) in England, as well as a study (4 - 8%) by Gies et al. (1998) in Brisbane, Australia. The personal ultraviolet radiation exposure journals of the children and adolescents were used to determine the timing of exposures, duration of exposures and nature of outdoor activities and these were then related to their daily ultraviolet radiation doses. Of all the factors considered, the nature of an individual's activity was found to have the strongest influence in determining their ultraviolet radiation dose. An activity model was derived in order to investigate the effect of activity on ultraviolet radiation dose, where three activity factors, namely swimming, walking and tennis, were calculated for a South African context and compared with those from previous international studies. It was found that the activity factors derived in this study were similar to Holman et al. (1983) and Herlihy et al. (1994) and may be used in an activity model to estimate individual erythemal ultraviolet radiation dose for a particular activity. The value of this innovative activity model lies in its ability to predict individual ultraviolet radiation dose and this may help to emphasise the importance of responsible outdoor behaviour. A mannequin was used to quantify the anatomical distribution of erythemal ultraviolet radiation under clear sky and overcast conditions. It was found that the vertex of the head and shoulders received the highest erythemal ultraviolet radiation doses under both conditions. This was then related to the erythemal ultraviolet radiation doses of the children and adolescents as recorded by the polysulphone film badges in order to identify anatomic sites susceptible to high erythemal ultraviolet radiation doses. Behaviour alternatives and ultraviolet radiation protective mechanisms were discussed and recommendations made for children and adolescents residing in Durban. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

Commercial sunscreen products are used to protect the skin against hannful ultraviolet (UV) radiation that can induce skin cancer at high dosage. These products contain UV filters that can reflect, scatter or absorb UV light. The chemical UV filters responsible for the absorption of UV radiation can be photochemically modified and as a result reduce the efficacy of the sunscreen formulation. This study focused on the possible use ofplant polyphenols as potential stabilisers of photo-unstable sunscreen chemical absorbers. The photo-instability of some sunscreen absorbers results in radical formation; this prompted the use of the plant, Sutherlandia microphylla (Cancer Bush plant), as a potential photostabiliser. The Cancer Bush plant is used by the indigenous people of South Africa to treat AIDS and cancer. The radical scavenging properties of polyphenolic compounds present in the plant are possibly responsible for the plant's anti-tumour and anti-IDV properties. Therefore, these Cancer Bush polyphenols could possibly be used to photostabilise photo-unstable sunscreen absorbers. Potential polyphenolic photostabilisers from the Cancer Bush plant were extracted by means of various polyphenolic extraction methods. These extracts were analysed by gas chromatography (GC), high-performance liquid chromatography (HPLC), UV spectroscopy and gas chromatography-mass spectrometry (GC-MS). The phenolic content and the antioxidant activity ofthese extracts were investigated by means of the Folin-eiocalteu reagent (FCR) and the diphenylpicrylhydrazyl (DPPH) radical assays respectively. Polyphenols were also extracted from various Rooibos teas and compared with those extracted from the Cancer Bush plant. Both the Cancer Bush and various Rooibos tea extracts were found to contain simple phen~lics and potential polyphenolic compounds. The Cancer Bush extracts as well as the Rooibos tea extracts together with the specific polyphenols, epicatechin and rutin, were assessed for their ability to photostabilise sunscreen absorbers. The photostability of the chemical absorbers in the absence and in the presence of the polyphenol extracts was investigated by UV spectroscopy, by monitoring their absorption spectra during irradiation with solar-simulated radiation. These extracts inhibited the photodegradation of the absorber avobenzone. The photostability of avobenzone is solventIntroduction III dependent hence the investigations were carried out in three solvents, namely, cyclohexane, ethyl acetate and dimethylsulfoxide. Additionally, the cause ofthe instability ofavobenzone in these solvents was investigated by means of DV spectroscopy, HPLC and nuclear magnetic resonance spectroscopy. The oxygen dependency of the photo-instability of avobenzone was also determined. The photo-instability of avobenzone was found to occur as a result of photoisomerisation and!or photodegradation, depending on the solvent. Avobenzone photoisomerised extensively in dimethylsulfoxide and photodegraded appreciably in cyclohexane, whereas both processes occurred to a similar extent in ethyl acetate. Photoisomerisation only occurred in the presence of oxygen whereas photodegradation occurred irrespective of oxygen. The Cancer Bush and various Rooibos tea extracts as well as other polyphenols photostabilised avobenzone in ethyl acetate and dimethylsulfoxide but not in cyclohexane. This photostabilisation effect was potentially due to the radical scavenging ability of polyphenols which prevented the oxygendependent photoisomerisation, but not the oxygen independent photodegradation process from occurring. / Thesis (M.Sc.)-Chemistry-University of KwaZulu-Natal, 2005

'Hot particle' skin dosimetry calculations are commonly performed using homogeneous dose-point kernels (DPK) in conjunction with scaling and backscatter models to account for non-homogeneous geometries. A new scaling model for determining the actual DPK for beta-particles transmitted by a high-Z source material has been developed. The model is based on a determination of the amount of mono-energetic electron absorption that occurs in a given source thickness through the use of EGSnrc (Electron Gamma Shower) Monte Carlo simulations. Integration over a particular beta spectrum provides the beta-particle DPK following self-absorption as a function of source thickness and radial depth in water, thereby accounting for spectral hardening that may occur in higher-Z materials. Beta spectra of varying spectral shapes and endpoint energies were used to test our model for select source materials with 7.42 < Z ��� 94. A new volumetric backscatter model has also been developed. This model corrects for beta-particle backscattering that occurs both in the source medium and in the atmosphere surrounding the source. Hot particle backscatter factors are constructed iteratively through selective integration of point-source backscatter factors over a given source geometry. Selection criteria are based on individual source-point positions within the source and determine which, if any, backscatter factors are used. The new scaling model and backscatter model were implemented into the DPK-based code VARSKIN 4 for extensive dose testing and verification. Verification results were compared to equivalent Monte Carlo simulations. The results demonstrate that significant improvements can be made to DPK-based models when dealing with high-Z volumetric sources in non-homogeneous geometries. / Graduation date: 2013

Ultraviolet (UV) radiation damages both eukaryotic and prokaryotic cells by causing the formation of free radicals which damage cell membranes and DNA. Antioxidant vitamins have been shown to protect cells from UV-induced damage by scavenging free radicals. The protection of skin and its normal flora is necessary for the health of individuals in resisting diseases caused by microorganisms and delaying the long-term damage caused by UV radiation.This research investigated the effects of the antioxidants vitamin A and ascorbic acid, as well as UV-irradiation on both prokaryotic (Staphylococcus epidermidis) cells and eukaryotic (human fibroblast skin) cells. This information is important in determining the effects of vitamin treatment on skin and its normal flora.Results indicate that ascorbic acid is rapidly (within six hours) degraded after being dissolved in water or medium. Treatment of cells with ascorbic acid must take into account this rapid degradation. S.epidermidis cells were protected from UV-induced damage by treatment with ascorbic acid but were more sensitive to UV-irradiation when treated with vitamin A. Human fibroblast cells treated with ascorbic acid did not exhibit morphological changes when compared to untreated cells. / Department of Biology

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 198-219). / Also available by subscription via World Wide Web / xvii, 219 leaves, bound ill., some col. 29 cm