Many heavy metals are essential for biological functions; however some of these metals,
especially at high concentrations, can have serious adverse effects on humans. The main
sources of heavy metal exposure are through agriculture, transport, mining and related
operations. South Africa has a thriving mining industry and is known for its rich mineral
resources, but due to the incorrect method of disposal of the waste from these mines,
substances, including heavy metals, get into the water and air supply, affecting the people
living in close proximity to these mines. Exposure is through inhalation of contaminated air
and consumption of contaminated food and water. The most vulnerable to heavy metals are
the developing fetus, because of the high rate of cell division and differentiation.
In the current study, two heavy metals cadmium (Cd) and chromium (Cr) were chosen based
on the possibility of being exposed to them in South Africa. Thus, the aim of this study was
to investigate the possible cellular effects of the heavy metals Cd and Cr alone and in
combination, at different concentrations, on brain, liver and kidney tissue by using a chick
embryo model.
This model was successfully implemented over a 14 day period after which the embryos
were terminated and the brains, livers and kidneys removed and processed for light- and
transmission electron microscopy (with energy dispersive spectroscopy and electron energyloss
spectroscopy). In addition, the effect of Cd and Cr alone and in combination on DNA
structure and micronuclei formation was evaluated. The levels of the major antioxidant
component, glutathione was determined in the brains of the chick embryos. At low concentration of Cd and Cr alone and in combination, a hormesis effect was observed
in the survival rates and weights of the chick embryos, while at x1000 physiological dose
(PD) Cr and Cd alone and in combination the effects were toxic. The majority of viable
embryos did not have any macro-anatomy abnormalities.
Morphological evaluation of the brain, liver and kidney samples revealed that Cd caused
severe alterations at its highest concentration with minor alterations at the lower
concentrations. Cr and the metal combination groups on the other hand, only caused
minimal alterations throughout the concentration ranges evaluated. The presence of Cd and
Cr alone and in combination in the liver tissue was confirmed with the electron energy-loss
spectroscopy analysis that detected these metals in the nuclei, mitochondria and Golgi
complexes of the hepatocytes. This might contribute to the ultrastructural changes observed
in this organ. The genotoxicity testing on the red blood cells revealed no substantial
differences, as only a few micronuclei were present.
Although heavy metals cause DNA damage through an indirect mechanism of oxidative
damage, the presence of Cd and Cr in the nucleus and mitochondria indicates that these
metals may have a direct effect on DNA structure. With DNA agarose gel electrophoresis it
was found that Cd and Cr alone and in combination caused DNA fragmentation. In the brain,
GSH levels were normal; however changes may be the result of Cd and Cr causing the
depletion of other antioxidant elements such as glutathione reductase, glutathione
peroxidase, superoxide dismutase and catalase.
In conclusion, this study indicates that Cd and Cr alone and in combination are toxic to the
chick embryo. Cd is more toxic than Cr, and both metals accumulate in the nuclei and
mitochondria where they induce damage either through oxidative and/or other mechanisms
associated directly with DNA damage. / Dissertation (MSc)--University of Pretoria, 2014. / tm2015 / Anatomy / MSc / Unrestricted
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:up/oai:repository.up.ac.za:2263/46019 |
| Date | January 2014 |
| Creators | Venter, Chantelle |
| Contributors | Oberholzer, Hester Magdalena, Taute, Helena |
| Publisher | University of Pretoria |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Rights | © 2015 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
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