Abstract
D.Phil.
By virtue of its position on the eastern border of South Africa, the Kruger National Park (KNP)
receives the flow of six main riven, of which the greater part of the specific catchment areas are
situated upstream from the park itself. The Olifants River has the largest catchment area both in
size and in proportion of catchment area beyond the park boundary. Increased competing demand
for water by the urban, industrial, mining and agricultural sectors within the catchment boundaries
of the Olifants River has focused attention on the ecological water requirements of the river. Of
particular concern was the high degree of mineralisation of the Olifants River due to mining
activities on the western boundary of the KNP.
When one considers the demand for water by the Kruger National Park it is evident that water is
required for more than one use, i.e. for potable use, game watering and ecosystem (aquatic and
riparian) maintenance. In order to facilitate proper water quality management it is necessary to
develop a comprehensive water quality management plan for the river. The development of such a
plan requires a thorough understanding of the fate and effects of pollutants in the environment. It
is furthermore important to have reliable information on the trends and status of important water
quality determinants in these systems. This study was therefore aimed at investigating the metal
ecotoxicology of the lower Olifants River and the Selati River, a tributary of the Olifants River
which flows through the Phalaborwa area.
Water quality is a driving variable in aquatic ecosystems. Full assessment of water quality of the
Olifants River included evaluation of the physical, chemical and biological attributes of the system.
The difference between the physical/chemical and biological attributes is that the former provide
an instantaneous and often specific assessment of the water quality, whereas the latter integrate
changes in the system over time. Water and sediment samples were collected bi-monthly from
February 1990 to February 1992 at six stations along the lower Olifants River, one in the Selati
River and one in the Letaba River. At each of these sites physical and chemical water quality
characteristics were measured. Two metal bioaccumulation indicator species, Labeo rosae and
Oreochromis mossambicus, were also sampled during the same period at three stations in the
Olifants River and at the Selati River sampling station. Two additional surveys were undertaken to
reference sites in the KNP (i.e. Pioneer Dam, and Nhlanganini Dam) during February 1992 and
April 1992 respectively. Tissue samples (muscle, gill, liver, gonads, fat and blood) were collected
and analysed for Cr, Cu, Fe, Mn, Ni, Pb and Zn using atomic absorption spectrophotometry.
The routine monitoring of chemical and physical water quality attributes produces large quantities
of complex data which are often difficult to interpret. To reduce the complexity, data may be
standardised and summarised into an index. The Aquatic Toxicity Index (ATI) that was developed
Metal Ecotoxicology in the Olifants River it
Summary
during this study presented the water quality of all the sampling stations, during each survey as a
single value. This value reflected the water quality's suitability-for-use by fish at the different
sampling stations. The ATI showed definite temporal and spatial trends in water quality in the
Olifants River. The Selati River was the main contributing factor to the poor water quality
measured in the Olifants River within the KNP. This was due to high TDS, metal and fluoride
concentrations. Deterioration of the water quality was experienced during flood conditions when
the turbidities and total metal concentrations increased. The water quality generally increased
between summer and winter surveys (February to June).
Bioindicators are species used to quantify biologically available level of metals in the aquatic
ecosystem. These organisms take up metals from the ambient water and from food, and the
concentrations in their tissues (or changes in concentrations) provide a time integrated measure of
metal bioavailability. Temporal bioavailability of metals in the tissues of the bioindicators showed
similar trends to the water quality. Highest metal concentrations were measured in fish tissue
samples collected during flood conditions (December 1990) and during low-flow conditions (June
to October). This was attributed to increased exposure due to metal adsorption to suspended
sediments during the flood conditions and to increased ambient metal concentrations during lowflow
conditions. The distribution of metals in tissues varied based on the uptake, depuration and
metabolism strategies for each metal. In general the gill tissue bioaccumulated the highest metal
concentrations, with only Cu and Fe occurring in higher concentrations in liver tissue. Significant
positive correlation's were found between bioaccumulation in muscle tissue and the other tissues:
Space-bulking and time-bulking of results were carried out to elucidate spatial bioaccumulation
patterns. The highest bioaccumulation of Cu, Pb and Ni were recorded in samples from the Selati
River, whereas Zn and Cr concentrations were the highest in the Olifants River.
An equilibrium partitioning (EP) technique was used to integrate bioaccumulation data and metal
concentrations in different phases of the water and sediment and produce specific Cu and Zn
criteria for the Olifants and Selati rivers. Although there is a multitude of data available for Cu
and Zn toxicity and BCF's, the quality criteria produced during this study, for the first time, made
use of results obtained under local conditions.
The results from bioaccumulation studies carried out in the field can not provide information
regarding the potential effects or the risks the metals may pose to the exposed organisms.
Therefore the susceptibility of the organisms to metal contamination can be determined using
laboratory studies. Physiology is toxicology's closest relative and contributes markedly in
assessing the toxicological risk of metals. Bioassays were conducted to determine the uptake
kinetics, acid-base disturbances and haematological effects of a metal mixture containing Cu, Fe
and Zn on Tilapia sparrmanii. The effects of the individual metals (Cu, Fe and Zn) and different
Metal Ecotoxicology