Exfoliative cytology as a biomarker in the assessment of cadmium and zinc pollution in the liver of Oreochromis mossambicus (cichlidae)

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dc.contributor.author Mokae, Motsidisi Lorraine Lolo
dc.date.accessioned 2008-10-14T11:35:58Z
dc.date.available 2008-10-14T11:35:58Z
dc.date.issued 2008-10-14T11:35:58Z
dc.date.submitted 2005
dc.identifier.uri http://hdl.handle.net/10210/1195
dc.description M.Sc. en
dc.description.abstract The two most important aspects that give rise to this study are the assumptions that: • water is humanity’s most revered natural resource and • the alarming rate at which natural water systems are contaminated. Water is undoubtedly the most precious natural resource at humanity’s disposal. It is essential for the livelihood of both aquatic and terrestrial animals. However, people disregard water systems as well as organisms dependent on them or inhabited by them. The pollution of water reserves has been exacerbated by the need to industrialise, urbanise and introduce all relevant technological aspects to feed humanity’s ever-changing socio-economic status. The pollution of dams, rivers and now lately the oceans continues unabated. A few regulatory laws are however in place, although total disregard for these laws is still the norm. In the last decade there has been an increasing awareness of environmental pollution and the way it impacts on all living systems. Scientists, environmentalists and ordinary people alike have realised the need to establish critical concentration levels for pollutants. For zoologists, the aim of keeping water reserves clean is mainly to preserve the large and diverse population of aquatic animals in them, to ensure that only a few species become extinct. Toxicity testing of animals in the laboratory provides a crude account of what actually happens in the field setting. The results emerging from such tests however, provide useful and essential information, especially in relation to aquatic animals and the general condition of their environment. Fish are susceptible to variations in the environment and respond more sensitively to pollutants than most other animals. Oreochromis mossambicus species were used in this study because they are indigenous, easy to manage, accessible throughout the year and inexpensive. There is also limited information available on the effect of pollutants on endemic South African fish species. The liver was chosen as a test organ because it is a complex organ; one with a myriad of metabolic functions that include detoxifying ingested pollutants, synthesis of bile and maintenance of blood glucose concentration. The high degree of metabolic activities of hepatocytes renders them vulnerable to pollutants. Hepatocytes are thus expected to be the primary targets of toxicity lesions and can therefore serve as sensitive biomarkers. Biological biomarkers indicate prior exposure to toxic pollutants and the response of the organisms to these pollutants. Cadmium and zinc are two among many metals that occur naturally in the aquatic systems. Since metals rarely occur singly, South Africa’s natural water systems are more likely to contain a number of different pollutants at one time. In order to determine the effect of cadmium and zinc on organ systems, it is imperative that other metals be drawn into the discussion because pollutants occur as components of metal mixtures and not as isolated entities. Certain metals have no known biological functions while others are essential to the biota and become patently toxic when the nutritional supply exceeds the optimal amount. Zinc is an essential trace element, but is known to affect the histology of most organs in various animals when present in high concentrations. Cadmium is given priority in this study mainly because of its bioaccumulative nature in tissues. Its toxicity is particularly effective in that it is not eliminated by most organisms. Instead it accumulates in different organs, mainly the skeletal bones. Exfoliative cytology is the study of normal and abnormal desquamated cells from various sites in the body. There are three main types of cellular exfoliation from which cells can be sampled. These include natural spontaneous exfoliation, artificial or abrasive exfoliation and aspiration cytology. Although exfoliative cytology is used as a screening mode in a large number of asymptomatic patients in an effort to detect subclinical diseases, it has become more of a diagnostic procedure in human cytology. In this study, exfoliative cytology was used to determine the effect of a mixture of cadmium and zinc pollution in the liver cells of the Oreochromis mossambicus species. The advantages of exfoliative cytology are that individual liver cells could be used as biomarkers in determining aquatic metal pollution. Occult diseases in fish can be detected with a high degree of sensitivity and specificity by using cytological evaluation. Quality control in large fisheries, where metal pollution from too frequent administration of medication is a predictable occurrence, can be performed on a massive scale. Exfoliative cytology also provides a rapid, cost effective and simple means of diagnosis. In the management of ecosystems, rapid and effective techniques are essential in detecting abnormalities before the entire organism, and subsequently the entire population is compromised. en
dc.description.sponsorship Prof. J.H.J. van Vuren en
dc.language.iso en en
dc.subject Effect of heavy metals on fishes en
dc.subject Effect of heavy metals on Mozambique tilapia en
dc.subject Zinc toxicology en
dc.title Exfoliative cytology as a biomarker in the assessment of cadmium and zinc pollution in the liver of Oreochromis mossambicus (cichlidae) en
dc.type Thesis en

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