Abstract
M.Sc.
South Africa is renowned for its exploitable mineral resources and continues
to be a major player in the world’s mineral markets. The country is well
known for containing the world’s largest gold and platinum repositories and
electroplating industries, which is the major cause for delivering by-products
such as cadmium (Cd), chromium (Cr) and nickel (Ni).
Environmental pollution caused by active mining and seepage from closed
mines, continuously threatens South African water resources. Such pollution
can cause a shift in water chemistry and increase the availability of certain
metals to the living organisms of such a system. Even at low concentrations
metals are amongst the most toxic environmental pollutants. As a result of
their persistence and capacity to accumulate in the environment, metals
have a lasting detrimental effect on the ecosystem. Although there is
progress in the treatment of metallic wastes, the discharge thereof by
industries is still a serious water pollution problem.
In the past, chemical analysis of water has proven to be of great use for the
detection of pollutants within the environment. The value of chemical
analysis alone has become limiting, as chemical analysis supplies information
on the levels of chemicals at a certain time. Furthermore, the monitoring of
water quality variables often does not reflect long-term events that may play
a critical role in determining the ecosystem health. It is now generally
understood that measurements of only the physical and chemical attributes
of water cannot be used as surrogates for assessing the health of an aquatic
ecosystem. The new trend is to incorporate biological monitoring into
Abstract
existing monitoring strategies. Fish are entirely dependent on the aquatic
environment for their survival, rendering them a good monitor of water
pollution.
Macroscopic changes in organs are preceded by changes at the tissue,
cellular or molecular level. These changes are the net result of adverse
biochemical and physiological changes within an organism. Histological
analysis is a therefore very sensitive parameter and a valuable technique in
determining cellular changes in target organs as a result of exposure to
stressors. Fish histology can thus be used as an indicator of exposure to
contaminants and assess the degree of pollution.
Because of the subjective nature of morphological studies correlations with
other quantitative studies are difficult. However, incorporation of
quantitative methods is essential to the continued development of
histopathology as a biomarker of pollution exposure, and to the
interpretation of histological responses. The aim of this study is to
qualitatively and quantitatively describe the toxic induced histological
changes in the selected organs of Oreochromis mossambicus after acute
exposure to Cd, Cr and Ni. Fish were exposed to 10% (n=20) and 20%
(n=20) of the LC50 concentration of Cd, Cr and Ni respectively under
controlled conditions (23 ± 1°C) for 96 hours in an environmental room with
a control group (n=5) for each exposure.