Browsing by Author "Martincigh, Bice Susan."

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Adsorption of selected pollutants from aqueous solutions onto modified carbon nanotubes.
(2015) Oyetade, Oluwaseun Akinwole.; Martincigh, Bice Susan.; Nyamori, Vincent Onserio.; Jonnalagadda, Sreekantha Babu.
The significance of wastewater remediation before its discharge into the aquatic environment cannot be overemphasized. Adsorption has been proven to be effective for the removal of toxic pollutants from industrial effluents and/or wastewater, due to its simplicity in operation and the possibility of regenerating sorbents for reuse. This concept was exploited to achieve the effective removal of toxic contaminants from simulated wastewater. Carbon nanotubes, a fascinating member of the carbon family, possessing unique physical and chemical properties, have been reported as superior adsorbents for wastewater remediation purposes. Their large specific surface areas and porosity, hollow and layered structures, and great mechanical and thermal stability, makes them good candidates as sorbents for wastewater treatment and contamination control. This thesis interrogates the efficacy of carbon-structured nanomaterials containing multiwalled carbon nanotubes (MWCNTs) as the backbone, for the removal of divalent metal ions and organic contaminants from aqueous solutions. In this work, a novel adsorbent was successfully synthesized by incorporating a nitrogen-donor ligand (4-phenyl-2, 2':6', 2''-terpyridine) onto MWCNTs to afford nitrogen-functionalized MWCNTs (MWCNT-ttpy). The effectiveness of this sorbent towards the removal of divalent metal ions (Pb2+, Cd2+, Zn2+, Hg2+ and Cu2+), and organic contaminants (bisphenol A and ibuprofen) from aqueous solutions was investigated. The adsorption uptake of these pollutants onto MWCNT-ttpy was compared with that of acid-functionalized MWCNTs (MWCNT-COOH) to determine the sorbent with best removal efficiencies. Further, magnetic nanocomposites containing cobalt ferrite nanoparticles and MWCNT-COOH were synthesized in varying ratios to investigate their effectiveness for the removal of rhodamine B from aqueous solutions. All nanomaterials synthesized were characterized by means of TEM, SEM, TGA, BET, FTIR and Raman spectroscopy before application. Batch adsorption experiments were conducted to determine the effects of pH, contact time, adsorbent dose, initial adsorbate concentration and temperature for each sorption process in order to evaluate the best experimental conditions necessary for pollutant removal. The experimental data were fitted into the pseudo-first order, pseudo-second order, intraparticle diffusion and Elovich models to determine the dynamics and rate-determining step of the adsorption processes. The mechanism of the process was investigated by fitting the experimental data into various two- and three-parameter isotherms. iii The application of MWCNT-ttpy for the removal of both heavy metal ions and organic pollutants demonstrated much enhanced uptakes than MWCNT-COOH. The incorporation of nitrogen onto MWCNT-COOH significantly improved the affinity towards the removal of metal ions, forming strong electrostatic and coordination interactions between the active sites on the adsorbent and metal ion cations. Increasing hydrophobicity of MWCNT-ttpy over MWCNT-COOH accounted for the enhanced removal of bisphenol A and ibuprofen, since their uptake is primarily decided on by the hydrophobic nature of sorbates. Further, the application of both MWCNT-COOH and magnetic carbon nanotube-cobalt ferrites nanocomposites showed good removal efficiencies for rhodamine B from aqueous solution, with the best uptake achieved by using MWCNT-COOH. However, the magnetic nanocomposites give an advantage of separation under magnetic influence, hence, limiting inconveniences encountered during separation. The kinetics of adsorption were mostly described by the pseudo-second order and the Elovich models, while the equilibrium data were best described by the Langmuir and the Sips isotherm models. The thermodynamic parameters of adsorption, namely, the change in Gibbs energy (ΔGº), change in enthalpy (ΔHº) and change in entropy (ΔSº) were estimated for each adsorption process. The adsorption of all adsorbates were endothermic in nature except in the case of ibuprofen and Cd2+ which exhibited an exothermic process. All adsorption processes described in this study were spontaneous, implying the feasibility of the sorbents for the removal of targeted pollutants from wastewater. Desorption studies aimed at regenerating the adsorbents for reuse were successful. High recovery efficiencies between 60-95% were achieved by using eluents such as 0.1 mol dm-3 HCl for metal ions, and ethanol and acetone/acetic acid for organic contaminants. This process averts the production of secondary pollutants, supporting the reutilization of both the adsorbents and the adsorbates. Thus, all adsorbents used in this study were efficiently regenerated by using simple conventional chemicals and can be reused for the removal of targeted pollutants from aqueous solutions. The competitive adsorption of Pb2+, Cd2+, Zn2+ and Cu2+ and the binary adsorption of bisphenol A and ibuprofen onto MWCNT-ttpy was also investigated in both single-solute and multi-component adsorption systems. The sorption of metal ions onto MWCNT-ttpy was in the sequence Cd > Pb > Cu > Zn and Pb > Cu > Cd > Zn in single-solute and multicomponent systems, respectively, while the removal of ibuprofen was higher than that of bisphenol A in a typical binary adsorption system. For the first time, the competitive sorption of organic contaminants (bisphenol A and ibuprofen) in the presence of metal ions (Cd2+ and Pb2+) onto nitrogen-functionalized MWCNT was investigated. The iv study revealed a cooperative mechanism of adsorption between metal ions and organic pollutants in a multicomponent system. Thus, the novel adsorbent proved effective for the removal of metal ions, bisphenol A and ibuprofen in both single-solute and multicomponent adsorption systems. MWCNT-ttpy also proved remarkably effective for removing three heavy metal ions, Pb2+, Cu2+ and Zn2+, in three different real-life water samples, obtained from the Umgeni River. Removal efficiencies greater than 95% were achieved for all three metal ions. The modification of MWCNTs to afford both nitrogen-functionalized MWCNTs and cobalt-ferrite/MWCNT nanocomposites was successful. These sorbents exhibited excellent pollutant removal abilities, attributed to improved textural characteristics of the nanomaterials synthesized. The application of these sorbents for wastewater and industrial effluent remediation should be further explored for prudent management of water resources.
Analysis of skin preparations.
(2015) Navondo, Funani Thelma.; Martincigh, Bice Susan.
Abstract available in PDF file.
Application of N-doped TiO₂/Bi₂O₃/rGO nanocomposites as a photoanode material in dye- sensitized solar cells.
(2021) Ngwenya, Simphiwe Ntokozo.; Nyamori, Vincent Onserio.; Martincigh, Bice Susan.
Abstract available in PDF.
An assessment of the photostability of South African commercial sunscreens.
(2001) Bunhu, Tavengwa.; Martincigh, Bice Susan.
Abstract available in PDF file.
The Brix-Free water capacity and sorption behaviour of fibre components of sugar cane (Saccharum officinarum).
(2008) Hoi, Yin Lun Wong Sak.; Martincigh, Bice Susan.; Lionnet, Georges Raoul Edouard.; Autrey, Louis Jean Claude.
Milling data from sugar factories in Mauritius were examined from 1960 to 2004 to assess the trend in the quality of cane received at mills and the change in factory performance. A deterioration in overall quality was apparent due to the increased level of extraneous matter delivered in the cane supply. Comparison was made with available data from other countries in the world, notably those of South Africa and Australia. Controlled addition of extraneous matter to clean cane was effected under laboratory conditions to determine the relative impact of dry leaves, green leaves and cane tops on the quality of cane and the resulting juice, and to predict through derived equations, their impact on cane processing. The addition of dry leaves was found to have the most adverse effect followed by green leaves and cane tops. In the case of dry leaf addition to cane the detrimental effects were found to be masked by an increase in the concentration of solutes in the juice extracted. This phenomenon was thought to be due to the selective sorption of water (so-called Brix-free water) by dry leaves. To test this assertion, the sugar cane stalks of four different cane varieties aged 52, 44 and 36 weeks were separated into their component parts by means of a method devised in this work. There were nine component parts: stalk fibre, stalk pith, rind fibre, rind fines, top fibre, dry leaf fibre, dry leaf fines, green leaf fibre and green leaf fines which, on characterisation by Fourier transform infrared spectroscopy and scanning electron microscopy, were very similar except that stalk pith was more flaky and had a higher surface area than the others. Various analytical techniques were tested for the determination of Brix-free water. The most convenient method proved to be a refractometric method which was improved so as to be applicable to the wide range of cane components fibres studied. Statistical analysis of the Brix-free water content of the separated samples showed that when the combined effect of fibre and pith in the cane stalk of three ages was considered, the four cane varieties were not different. This was not the case for dry leaf, green leaf, top and rind. Of the nine cane components, stalk pith exhibited the highest Brix-free water value of about 20 g/100 g fibre, whereas all the other components exhibited values of about 15 g/100 g fibre, which are much lower than the traditionally accepted value of 25% for cane. The latter was found to be the fibre saturation point of bound water determined at 20 oC, which is the sum of dissolved and hydrated waters, and which is normally greater than the Brix-free water value as determined in this work. The water sorption characteristics of the various cane component parts were further investigated by making measurements to determine the equilibrium moisture contents at various water activity values. These data were used to construct adsorption isotherms. These were fitted to 17 existing isotherm models, of which two, namely, the Hailwood-Horrobin and Guggenheim-Anderson-de Boer models, gave the best fit. The sorbed water was subsequently characterised in terms of various parameters, namely, the monolayer moisture content, the number of adsorbed monolayers, the percentage of bound water, the total surface area for hydrophilic binding, the heats of sorption of the monolayer and multilayers, the net and total isosteric heats of sorption and the entropy of sorption. From the monolayer moisture content and the amount of “hydrated water” as calculated from the Hailwood-Horrobin model, it is clear that at EMC values between 0 and 5% (aw = 0 – 0.3), the non-freezable water is tightly bound to the surface of the fibre. The second region starts at EMC values from 5% to 10 – 15% (aw = 0.3 to 0.6 – 0.8) depending on the cane components, and the bound water in this region is termed the freezable water. The third type of water is essentially free water, it exists after the second region and ends at EMC values of about 25%. From this study, it is apparent that the Brix-free water as measured in this work measures the amount of water bound in the first two regions.
Characterisation of extracellular polysaccharides produced from a fungal pathogen of sugarcane.
(2016) du Clou, Heidi.; Martincigh, Bice Susan.
Abstract available in PDF file.
A comparative study of solvent extraction, Soxhlet extraction, steam distillation, headspace analysis and headspace solid phase microextraction for the extraction of volatile terpenoid compounds in the curry leaf plant (Murraya koenigii).
(2010) Govender, Hogantharanni.; Martincigh, Bice Susan.; Kindness, Andrew.
A comparative study was undertaken of different extraction methods for the isolation of volatile organic compounds from Murraya koenigii (curry leaf plant). The techniques studied included the traditional methods of extraction, namely, Soxhlet and solvent extraction as well as steam distillation. The solvent–free extraction techniques of headspace analysis and headspace solid phase micro-extraction (HS-SPME) were also investigated. In the evaluation of SPME, two different fibre coatings, poly(dimethylsiloxane) and poly(acrylate), were compared. Preliminary work to determine the effect of extraction parameters, such as extraction time, was carried out. The volatile oils in the fresh leaves of Murraya koenigii were isolated by the above-mentioned extraction methods and analysed by gas chromatography-mass spectrometry. The main aroma contributing compounds were identified by comparison of their retention times with those of standards and their mass spectra with those of known compounds contained in the National Institute of Science and Technology Standard Reference Database 1A (NIST 98). The essential oil contained mainly terpenes: monoterpene and sesquiterpene hydrocarbons. The constituents were identified and only the five selected analytes of interest, a-pinene, β-pinene, a-phellandrene, β-caryophyllene and a-caryophyllene were quantified in three of the methods, namely solvent extraction, soxhlet extraction and steam distillation. From the quantitative determination of the compounds of interest, steam distillation favoured the extraction of β-caryophyllene. The solvent and Soxhlet extractions showed no significant differences between the quantities obtained for a- and β- caryophyllene. The steam distillation and Soxhlet methods showed similar quantities of a-caryophyllene extracted. The extraction of the monoterpenes, a-pinene, β-pinene, and a-phellandrene, was favoured by the Soxhlet method of extraction. Quantification was difficult with HS-SPME and headspace analysis. Headspace analysis proved effective in the detection of the very volatile analytes. Headspace-SPME combined with GC-MS was found to be suitable for the identification of both monoterpenes and sesquiterpenes of M. koenigii. From this study, solvent extraction and Soxhlet extraction were found to be superior to the other methods studied for the characterisation and quantitation of the volatile organic compounds in essential oils of Murraya koenigii.
DNA cleavage, photoinduced by benzophenone-based sunscreens.
(2003) Sewlall, Avashnee.; Martincigh, Bice Susan.; Lamb, Jennifer Margaret.
The topical application of sunscreens is widely practised to protect healthy and photosensitive skins from the sun. The benzophenone-derived sunscreens, e.g. 2-hydroxy-4-methoxy benzophenone-5-sulphonic acid (or benzophenone-4) and 2-hydroxy-4-methoxy benzophenone (or benzophenone-3), were ranked as the second and third most frequently used sunscreens, respectively, by the United States Food and Drug Administration (FDA) in 1996. These sunscreens are categorised as being 'safe' and 'effective'. However, it is well known that the parent compound, benzophenone, undergoes rapid hydrogen abstraction reactions on irradiation and is an extremely powerful radical generator. In addition, benzophenone has been shown to be a potent photosensitizer of thymine dimers in deoxyribose nucleic acid (DNA). More astounding to the sunscreen industry is the recent discovery that a group of non-steroidal anti- inflammatory drugs (NSAIDs) having the benzophenone backbone, e.g. ketoprofen, not only form thymine dimers when irradiated with DNA in vitro, but also photosensitize double stranded supercoiled DNA making it prone to single-strand break formation. Both these lesions, if unrepaired, may contribute to mutagenesis, carcinogenesis, inherited disease and eventually cell death. The purpose of this investigation was to determine if a group of benzophenone-derived sunscreen agents has the ability to photosensitize the cleavage of DNA, whereby supercoiled DNA is converted to the relaxed circular and linear forms. The group of UV absorbers investigated in this study included benzophenone-4, benzophenone-3 , 2,4 dihydroxybenzophenone (or benzophenone-l), 2,2'-dihydroxy-4,4'-dimethoxy benzophenone sulphonic acid (or trade name Uvinul DS49) and 2-phenylbenzimidazole-5-sulphonic acid (or trade name Eusolex 232). For comparison the parent compound benzophenone and the NSAID ketoprofen, a well-known photocleaver, were also studied. Buffered aqueous solutions of the benzophenones were irradiated in the presence of DNA at wavelengths greater than 300 nm with an Osram 500 W/2 high-pressure mercury lamp in conjunction with a 10 mm thick Pyrex filter. The irradiated samples were analysed for DNA cleavage by agarose gel electrophoresis and for DNA binding by fluorescence spectroscopy. The photostability of the UV absorbers was also investigated. In addition, computational studies were conducted to obtain the lowest energy geometrical structures of these UV absorbers and hence determine if intercalation of these UV absorbers with DNA was possible. From the photostability experiments conducted, it is apparent that the benzophenone-based UV absorbers were stable to photodecomposition when irradiated with UV light. They behaved in a manner different from their parent compound benzophenone, and from ketoprofen, where substantial photodegradation occurred upon UV irradiation. This is indicative of the rapid photoreactivity of the benzophenone backbone. The relative photostability of the UV absorbers was not anticipated and was attributed to the substituents present on the benzophenone backbone. The agarose gel electrophoresis experiments however clearly showed that benzophenone, ketoprofen, benzophenone-l, Uvinul DS49 and Eusolex 232 cleave ?X174 DNA when irradiated with UV light at wavelengths greater than 300 nm, while benzophenone-3 and benzophenone-4 did not. For these UV absorbers with the exception of benzophenone-3 and benzophenone-4, the number of single strand breaks in the DNA increased compared to when it was irradiated in their absence. In addition, the supercoiled DNA was converted to the relaxed circular and linear forms, the latter of which was undetected in the absence of the UV absorbers. Binding of benzophenone, ketoprofen, benzophenone-l and Uvinul DS49 to calf thymus DNA was also detected by the fluorescence spectroscopy technique. However, this was not observed for Eusolex 232, benzophenone-3 and benzophenone-4, since they did not compete with ethidium bromide for DNA binding sites. Where DNA cleavage did occur, the mechanism of this interaction had to be determined hence the motivation for the computational studies. From computational studies using PM3 semi- empirical calculations, it was determined that the benzophenone-based UV absorbers investigated, apart from Eusolex 232, displayed non-planar geometrical structures. This indicated that DNA intercalation of these sunscreen agents with DNA would at best be very limited, since only one half of the molecule could possibly interact with the bases of DNA. For benzophenone, ketoprofen, benzophenone-l and Uvinul DS49, photosensitised type I and type II processes involving triplet energy transfer reactions has been identified in literature as being responsible for DNA cleavage. It was determined by ab initio calculations that Eusolex 232 exists in a planar structure unlike the other UV absorbers mentioned above that were non- planar. It was concluded that although Eusolex 232 has the ability to intercalate with the base pairs of DNA, it does not do so, as shown by its lack of binding to calf thymus DNA by the fluorescence spectroscopy study. Literature alludes to photooxidation by singlet oxygen in single stranded DNA via the type II reaction and type I electron transfer reactions in double stranded DNA as the mechanism responsible for DNA cleavage induced by Eusolex 232.
The effect of antioxidants on the Para-Aminobenzoic acid photosensitised formation of thymine dimer and singlet molecular oxygen.
(2005) Salim, Ali Mohammed.; Martincigh, Bice Susan.
On exposure to UV radiation DNA is damaged. The thymine cyclobutane dimer is one of the most significant of the lesions formed. This dimer is associated with the mutagenic and carcinogenic effect of UV radiation. It has been shown to cause skin cancer. Thymine dimerisation can be effected by direct irradiation or via an endogenous photosensitiser that is involved in energy transfer. This deleterious effect of UV radiation has prompted the use of sunscreens as photoprotectants. Para-aminobenzoic acid (PABA) is an active ingredient that was once widely used in sunscreen formulations. Reports of allergic reactions and staining by PABA have led to the discontinuation of its use in sunscreencontaining products. It has been shown to be absorbed by human cells and to. photosensitise the dimerisation of thymine in DNA. It can also photosensitise the formation of singlet oxygen. Singlet oxygen has been implicated in many photodynamic disorders, carcinogensis, free radical reactions and aging. Because the photochemical properties of PABA on DNA have been well established by a number of earlier researchers, it proved an appropriate choice of photosensitiser in order to determine the effect of vitamin antioxidants on the photosensitised formation ofthymine dimer and singlet oxygen. Vitamin E (a-tocopherol) and vitamin C (ascorbic acid) are two important antioxidants that have been extensively studied in free-radical reactions and cancer-related ailments. They are known to reduce the formation of thymine dimers and also quench singlet . oxygen. They are found extensively in sunscreen formulations because of their photoprotective properties. The photoprotection is due to both their absorptive and antioxidant properties. They are known to act either individually or synergistically by physical quenching or reaction with free radicals. Their abilities to reduce the PABA-photosensitised formation of thymine dimer have been studied in this work. The study involved investigating their individual abilities and the synergism by varying their concentrations, the concentrations of thymine and PABA, and the photon flux. The pH of the solutions was always maintained at 3.0. Analysis and quantification of the photoproducts was done by using reverse phase high perfonnance liquid chromatography with a photo diode array UV detector. Studies on the P ABA-photosensitised production of singlet oxygen and its quenching by the antioxidants were also carried out at pH 3.0. With this regard, irradiation time and concentrations of PABA and the two vitamins were varied. Thymine was subsequently introduced so as to investigate its effect on singlet oxygen fonnation. The presence and change in concentration of singlet oxygen was monitored by using N,N-dimethyl-4-nitrosoaniline, RNO. The change in absorbance of RNO was measured at 350 nm, which is its maximum absorption wavelength at pH 3.0. The fonnation of singlet oxygen was inferred from these measurements. PABA-photosensitised thymine dimer yield increased with an increase in irradiation time and an increase in the concentration of thymine. However, the yield decreased with an increase in the concentration of PABA. The presence of the vitamins C and E either acting alone or when combined had an effect on the yield of thymine dimer. Both the two antioxidants can increase or decrease thymine dimer yield. However, this depended on the concentrations of the reagents, the irradiation time and whether the two vitamins were in combination or alone. Therefore, both synergistic and antagonistic properties of the two vitamins were observed in the PABA-photosensitised thymine dimer fonnation. Singlet oxygen fonnation generally increased with an increase in irradiation time except for the experiments in which the two vitamins were present together. When the two vitamins were present, there was an increase in the fonnation of singlet oxygen with irradiation time for a few minutes then the fonnation remained constant despite an increase in the irradiation time. An increase in the concentration of PABA also increased the fonnation of measurable singlet oxygen. The introduction of the antioxidants either individually or together decreased the yield of singlet oxygen. The presence of thymine had different effects on the total amount of measurable singlet oxygen from those seen above. Generally, singlet oxygen formation increased with increase in concentration of thymine. Thymine in the presence of increasing concentrations of PABA showed different trends in the formation of singlet oxygen. These trends depended on the presence or absence of the antioxidants and whether the antioxidants were present individually or together. In this set of experiments, the presence of thymine resulted in an increase in the total amount of singlet oxygen formed. An exception to this is when vitamin E is introduced. In this case the presence of thymine indicated formation of a smaller amount of singlet oxygen. In both cases of the absence and presence of thymine, the trend in the formation of singlet oxygen with increase in concentration of any of the antioxidants varied depending on whether the antioxidant was alone or present with the other. From the above it is evident that both synergistic and antagonistic properties of the two vitamins are exhibited regarding their ability to quench singlet oxygen in aqueous solution. The synergistic property of the two vitamins is lost in the presence of thymine. This implies that in the experimental conditions studied, thymine can photosensitise singlet oxygen formation despite the presence of the two vitamins. It is highly likely that both chemical and physical quenching by vitamins C and E take place. Some observations suggested a possible chemical interaction between the photosensitiser (PABA) and thymine with the quenchers. More work needs to be done in this regard to test this hypothesis.
An experimental study of graphitic carbon nitride-based materials and selected metal-based semiconductors in organic solar cells combined with a computational study of perovskite solar cells.
(2023) Rono, Nicholas.; Nyamori, Vincent Onserio.; Martincigh, Bice Susan.; Kibet, Joshua K.
Abstract available in PDF.
The incorporation of impurities into sucrose crystals during the crystallisation process.
(1998) Lionnet, Georges Raoul Edouard.; Martincigh, Bice Susan.; Purchase, Brian.
The main objective of this work is to propose a mechanism for the transfer of impurities into the sucrose crystal. To this end the transfer of impurities into the sucrose crystal was investigated, under crystallisation conditions similar to those found industrially. Most of the impurities, namely, colour bodies, potassium, calcium and starch, were selected on the basis of their industrial importance, but some exotic species, namely lithium and nickel, were chosen to represent other mono- and di-valent ions respectively, and dyes, such as methylene blue, which have been used in work with single crystal sucrose crystallisation, were included to make the results more general. A parameter to measure the rate at which impurities are transferred into the sucrose crystal was proposed. Experiments, carried out in a pilot plant evaporative crystalliser, were performed to establish the effect of selected factors on both the concentrations of impurities found in the sucrose crystal, and on the rate at which these impurities are incorporated into the crystal. All the factors selected, namely the rate of crystallisation, the temperature, the concentration and type of impurity, the diffusivity of the impurity in concentrated sucrose solutions, and the crystal dimensions, are shown to influence the rate of impurity transfer. Only the concentration in the feed and type of impurity, however, affect the final concentration of the impurity in the crystal. Concepts involving partition coefficients and adsorption isotherms were also investigated. The experimental data did not fit the adsorption isotherm models well, but the values obtained for the partition coefficients were similar to those quoted in the literature when exchange types of reactions are operative. Activation energies have been measured, both for the rate of crystallisation of sucrose, and for the rates of impurity transfer. The values obtained, particularly for the rate of impurity transfer, indicate that a transport mechanism is effective. The experimental results have been used to investigate the relevance of two models, one involving a two-step approach and the other an interfacial process, for the incorporation of the impurity into the sucrose crystal. The results obtained indicate that the interfacial breakdown model describes the transfer of all the impurities studied here, except for starch.
The influence of primary and secondary nitrogen donor atoms on the thermodynamics of complex formation in aqueous solution.
(1987) Martincigh, Bice Susan.; Marsicano, Fabrizzio.
An investigation into the ultraviolet radiation exposure of children and adolescents in Durban.
(2002) Guy, Caradee Yael.; Diab, Roseanne Denise.; Martincigh, Bice Susan.
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.
An investigation of commonly used skin-lightening creams.
(2014) Niyibizi, Clementine.; Martincigh, Bice Susan.
Abstract available in PDF file.
An investigation of the complexes of zinc and germanium with 8-hydroxyquinoline.
(1991) Maharaj, Vanitha.; Martincigh, Bice Susan.; Salter, Leo F.
The experimental work described in this thesis is aimed at the elucidation of the speciation of the zinc and germanium 8-hydroxyquinoline systems. A knowledge of this speciation could aid in modelling the kinetics of solvent extraction of zinc and germanium with 7alkyl derivatives of 8-hydroxyquinoline. In this study the stability constants of the ligand 8hydroxyquinoline with the ions H+, Zn2+ and Ge4+ have been investigated by potentiometry at 25°C in a partially aqueous medium. A titration technique was used in which the hydrogen ion concentration was monitored using a glass indicating electrode. The partially aqueous medium comprised of O. 1 mol dm- 3 NaCl04 in 60% (v/v) dioxane and the concentration levels of the reagents were at least millimolar. The analysis of the potentiometric data was carried out with the aid of the computer programs HALTAFALL, ESTA and STATGRAPHICS. The results obtained for the systems involving the H+ and Zn2+ ions compare with those reported in the literature. The stability constant of a protonated species in the zinc-8-hydroxyquinoline system (ZnLH) was established for the first time. Precipitates obtained from the Zn2+ titrations were identified as zinc 8-hydroxyquinolate dihydrate. The germanium 8-hydroxyquinoline system has not been studied previously via potentiometry techniques. The complex hydrolysed species of germanium in aqueous solutions and the unusual features displayed in the formation curves increased the complexity of species selection. Although a suitable model of the species present could not be determined some evidence suggests the presence of protonated species. Hence, a prerequisite for resolving the germanium-8hydroxyquinoline system could be a more complete understanding of the hydrolysis of germanium in the partially aqueous medium used.
Organic flame retardants in the indoor environment.
(2014) Abafe, Ovokeroye Akpojevwe.; Martincigh, Bice Susan.
Flame retardants (FRs) have become ubiquitous contaminants found in humans, animals, various outdoor environments, e.g. air, soil, sediment, etc., and indoor environments particularly, homes, automobiles, classrooms and workplaces all over the world. These chemicals are global contaminants of concern as they are persistent, can bioaccumulate, biomagnify and have potential for long-range atmospheric transport. Most FRs are toxicants to human health since they affect thyroid hormones, endocrine systems and neurobehavioural development and are possibly carcinogenic. The overall hypothesis of this study is that the use of FRs in consumer goods and materials is leading to contamination of indoor environment at levels that may be detrimental to human health. In this study, analytical methods based on gas chromatography-electron impact/mass spectrometry and liquid chromatography electrospray ionization/mass spectrometry were developed and/or validated for the separation, identification and quantitation of various classes of FRs. The FRs investigated included polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), tetrabromobisphenol A (TBBPA) and organophosphate esters [tris(1,3-dichloro-2-propyl) phosphate (TDCPP), tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCPP) and triphenyl phosphate (TPP)]. These were measured in indoor dust from a wide range of microenvironments, including homes, offices, classrooms, automobiles, three workplaces – an e-waste recycling site, a polyurethane factory and a textile industry – and an in vitro human gastro-intestinal tract (GIT). The measured concentrations of the FRs were used to estimate the exposure of toddlers, teenagers and adults to the FRs of interest via dust ingestion and in some cases dermal absorption of dust by using various exposure scenarios. The relative importance of each exposure route was assessed for the studied population groups. The potential sources of the FRs in the different microenvironments were established by using various advanced parametric and non-parametric statistical tests. Causes of variability in indoor dust concentrations of FRs were elucidated. Two types of in vitro GIT models mimicking the enzymatic and physiochemistry preponderant for a FED and a FASTED state were developed, validated and applied for the first time to study the oral bioaccessibility of organophosphate esters and also to study the bioaccessibility of PBDEs. Strong relationships were found for the bioaccessibility of OPEs and their water solubilities as well as the log Kow of PBDEs.
A photochemical investigation of two suncreen absorbers in a polar and a non-polar medium.
(2002) Panday, Rivash.; Martincigh, Bice Susan.
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.
The photochemistry and photostabilization potential of plant extracts on sunscreen absorbers.
(2014) Ollengo, Moses Abednego.; Martincigh, Bice Susan.
Abstract available in PDF file.
The potential of plant polyphenols as natural photostable sunscreen active ingredients.
(2022) Sowman, Serina Pooja.; Martincigh, Bice Susan.
Protection from the sun dates to prehistoric times as a measure against the deleterious effects of solar ultraviolet (UV) radiation. Overexposure to this harmful UV radiation is a leading cause of pathological changes of the skin, such as erythema and the worst being skin cancer. Commercial sunscreen products contain UV filter substances that are designed to protect human skin from erythema. These sunscreen products incorporate chemical UV-absorbing compounds and physical blockers that allow UV radiation to be reflected, scattered, or absorbed. This research discusses the use of certain organic UV absorbers and their importance in protection against the effects of UV radiation. The issues faced with certain UV absorbers are that they are susceptible to photodegradation over time, their degradation products can be phototoxic, and they provide protection only over a limited wavelength region. This causes a significant problem in sunscreen products as their efficacy is reduced. This has led to research on finding an alternative solution that can provide beneficial protection and maintain photostability. Interest was drawn to the plant kingdom for a more natural source of sunscreen absorbers since plants have developed various photoprotection mechanisms to counter enhanced levels of UV radiation. Polyphenols in plants have strong UV-absorbing properties that cover a broad spectrum, and they also possess excellent antioxidant activity. Therefore, they can play a dual role by acting as both natural absorbers of harmful radiation and quenchers of free radical damage also caused by sunlight. This project highlights the limitations in photostability of four commonly used chemical UV filters found in commercial sunscreen products, namely, avobenzone, benzophenone-9, 2-ethylhexyl-p-methoxycinnamate and 4-methylbenzylidene camphor, and involves testing a South African based plant extract to increase the current efficacy of sunscreens due to its photochemoprotective properties. Attempts at photostabilising the selected UV filters were made by incorporating extracts from Sutherlandia frutescens, also known as the Cancer Bush plant. Photostability studies were conducted on the extracts alone and when mixed with each of the sunscreen filters by means of UV-visible spectrophotometry. Phenolic compounds, namely, flavonoids and phenolic acids, were extracted, identified and quantified. From an industrial perspective, a cheaper alternative to the Cancer Bush plant is extracting polyphenols from commercial tea. Phenolic acids were extracted from Rooibos and green teas by means of a simple ethanol-water extraction technique. For comparison, the tea extracts were compared with the Cancer Bush extract. Green tea was found to provide excellent photostability. The phenolic acids that were extracted from the Cancer Bush plant and teas were analysed by high-performance liquid chromatography (HPLC). The identification and quantitation of six phenolic acids was achieved by reversed-phased HPLC. Identification of phenolic acids was achieved by matching the retention times and spectra of the extract components with those of phenolic acid standards. The identified phenolic acids were gallic acid, p-hydroxybenzoic acid, vanillic acid, caffeic acid, syringic acid and p-coumaric acid. The six phenolic acids were identified in the Cancer Bush ethanol-water extract and p-coumaric acid showed the highest concentration. Only three phenolic acids were successfully identified in the green tea extract and four in the Rooibos tea extract with the highest concentration being p-coumaric acid. A general sunscreen formulation was employed to assess the possible inclusion of polyphenols in sunscreens. Sunscreens were made with and without UV filters and photostability tests were conducted. A small amount of sunscreen was smeared onto a quartz plate and exposed to sunlight for a total of six hours. UV-visible spectrophotometric analysis was conducted at 30-minute intervals before and after exposure to determine their photostability. Sunscreen formulations containing plant extracts showed noteworthy photostability when compared with products without plant extracts by increasing the absorbance values. This shows that plant extracts may contribute synergistically to improve the efficacy of sunscreen formulations. The stability of the sunscreens was tested to determine formulation stability and safety. Furthermore, in vitro testing was applied to test sunscreen formulation parameters, such as, sun protection factor (SPF) and occlusion factor. Results show that the addition of the Cancer Bush plant improved the SPF of the sunscreen preparation. Therefore, this research has shown that the addition of the Cancer Bush extract can improve photostability and provide additional UV protection.
Safety assessment of skin-lightening formulations commonly available in the Nigerian market.
(2016) Mahmoud, Abdulkadir Ibrahim.; Martincigh, Bice Susan.
Abstract available in PDF file.