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School of Chemistry and Physics

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Browsing School of Chemistry and Physics by Author "Adeyinka, Gbadebo Clement."

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    The determination of organochlorinated pesticides and polychlorinated biphenyls in sediment, soil and water of the Msunduzi River, KwaZulu-Natal, South Africa.
    (2014) Adeyinka, Gbadebo Clement.; Moodley, Brenda.
    Persistent organic pollutants (POPs) are a major class of organic contaminants of serious global concern due to their persistence in the environment because of their stability to photolytic, chemical and biological degradation. POPs are mostly semi volatile organic compounds (SVOCs) and include polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs), which are toxic and capable of causing serious health disorders, such as, developmental and cancer related problems in animals and humans. Organic pollutants, such as, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are as well toxic as inorganic pollutants. There is limited information available on the concentration level and distribution pattern of organic pollutants within the KwaZulu-Natal Rivers as well as many studies done within this area have also only focused on inorganic pollutants. The lack of information and the need for knowledge on the organic pollutants in these rivers together with global concern for quality water has therefore prompted an investigation of the organic pollutants in the selected river. Therefore, the results and outcomes of this study could serve as a baseline assessment for various levels of government and scientific communities for future planning on the state of this river. The concentration patterns of selected priority pollutants (dirty dozen) made up of eight polychlorinated biphenyl (PCB) congeners and seven organochlorine pesticides (OCPs) together with six DDT metabolites were evaluated in sediment, soil and surface water during autumn, winter, spring and summer seasons from the Msunduzi River of KwaZulu-Natal, South Africa. Sediment, soil and water samples were collected at ten sites along the river in April 2013, July 2013, September 2013 and February 2014 that represented autumn, winter, spring and summer sampling seasons. Soil and sediment samples were dried and sieved while water samples were kept at 4 °C prior to the extraction. Soil and sediment samples were extracted by ultrasonication with dichloromethane (DCM) and water samples were subjected to liquid-liquid extraction using DCM. All sample extracts were cleaned up using multi-layered acidic/basic silica gel and all quality assurance steps were carefully observed. Both PCB congeners and OCPs were analysed and quantified in the sample extracts using gas chromatography–mass spectrometry (GC-MS). All the PCB congeners and OCPs analysed were detected in sediment, soil and water samples during all seasons. The results showed that sediment and soil samples contained the highest concentrations of both PCBs and OCPs with water samples having the lowest concentrations of all the analytes throughout the seasons. Concentrations of PCB congeners detected in the environment were found to be dependent on the number of chlorine atoms on the phenyl ring of PCB congeners, were PCB 180 exhibited the highest concentration and PCB 138 was found to be present in the lowest concentration. Total DDTs and endrin were the most predominant OCPs. The result of indicative indices suggested that the presence of DDTs could be attributed to the aged long degradation of DDT to its metabolites. The concentration patterns of the pollutants during the seasons were found to be in decreasing order of winter, spring, autumn and summer seasons. The concentrations detected in water samples during the seasons were also found to exceed the United State Environmental Protection Agency (USEPA) of 0.014 ng/mL and European Union (EU) 0.01 ng/mL recommended tolerable levels in surface and underground water respectively.
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    Partitioning studies of polychlorinated biphenyls between aqueous solution and soil and sediment systems of Umngeni river, KwaZulu-Natal, South Africa.
    (2018) Adeyinka, Gbadebo Clement.; Moodley, Brenda.
    The significance of soil and sediment physicochemical properties and the environmental parameters such as pH, temperature, ionic strength, humic acid (HA) and time on the partitioning action of eight selected polychlorinated biphenyl (PCB) congeners were critically evaluated in this study to better understand the mobility, transportation, fate and distribution of hydrophobic organic pollutants in environmental media. Natural soil samples used in this study were collected along uMngeni River of KwaZulu-Natal province of South Africa. The mineral properties of soil samples were determined using the Walkley Black method, barium chloride compulsive exchange method and Brunauer-Emmet-Teller (BET) adsorption-desorption isotherm. All these were employed to observe the surface characteristics of the modeled individual soil particle sizes. Scanning electron microscopy (SEM) equipped with energy disperse X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR) were used for the internal morphology and qualitative elemental analysis, as well as identification of possible functional groups in soil samples and commercial HA. Batch adsorption experiments were used for sorption studies. The results revealed that the amount of PCBs sorbed by soil was found to increase with an increase in contact time reaching equilibrium within 8 h. Among the soil chemical properties, soil organic matter was observed to correlate positively and play a more significant role in the sorption of PCBs. Soil samples with highest BET surface areas were related to the soil particle grain size. The sorption of PCBs onto soil was also found to decrease with an increase in the aqueous HA concentrations, and a change in the aqueous concentration of ionic strength was found to be less significant. Other important factors found to be more significant in the sorption were the degree of chlorination as well as stereochemistry of PCB congeners. The more hydrophobic and non-ortho (planar) congeners were found to contribute more significantly to sorption relative to the less hydrophobic and more ortho-substituted (nonplanar) congeners. Moreover, a decrease in the ratio of Si: (Al + Fe) was found to contribute positively to the sorption of PCBs. The kinetic studies on the partitioning of PCBs onto the soils was found to fit best with pseudo-second order, suggesting that the partitioning process of the selected PCBs between aqueous solution and active components in soil, involved more than onestep. Logarithmic values of organic carbon normalized sorption coefficient (log Koc) of the selected PCBs were found to decrease with an increase in the solution pH. The partitioning of PCBs onto the soils was also said to be temperature driven, where low aqueous temperatures encouraged morepartitioning of hydrophobic PCBs onto the soil. The Gibbs free energy (ΔG°) was found to be negative. Therefore, the thermodynamic studies showed that the PCB interaction with soil particle sizes was a spontaneous process. The role of initial PCB concentration on the partitioning was found to be L-type. This indicated that an increase in PCB concentration in the aqueous phase made it more difficult for PCB molecules to find a vacant site available for sorption onto the soil SOM.