Abstract
M.Sc.
Previous studies showed that the upper reaches of the Taaibosspruit catchment in the
north eastern region of the Free State, contains elevated concentrations of mercury in the
sediment. Additional laboratory-based bioaccumulation studies with sediment-dwelling
Chironomidae larvae revealed that the mercury was in a bioavailable form, but it was
uncertain to what extent this mercury was in the methylated organic form. Therefore, a
study to assess the extent of inorganic- and methylmercury contamination in the water
and sediment, as well as the uptake of this pollutant by aquatic and aquatic associated
biota was undertaken.
This study tested the hypothesis that bioaccumulation of mercury occurs in the different
trophic levels of the upper reaches of the Taaibosspruit ecosystem. The objectives of this
study were to determine the spatial and temporal physico-chemical characteristics of the
water and sediment of the Taaibosspruit system; to determine the extent of mercury
distribution within the water and sediment of the Taaibosspruit system; to determine the
degree of bioaccumulation and possible biomagnification of mercury by the biota from
the different trophic levels of the ecosystem in the Taaibosspruit system; to determine the
distribution of cadmium, chromium, copper, lead, manganese and uranium within the
water and sediment of this system, as well as the degree of bioaccumulation of these
metals by invertebrates and fish; and to determine whether the aquatic macroinvertebrate
community structures change along the mercury pollution gradient in the Taaibosspruit
system.
Sampling was done bi-annually at five sites during late high- and late low flow periods.
The reference site is situated on a tributary of the Taaibosspruit, which is not directly
influenced by discharges from the industrial complex. In situ water quality parameters
were determined at each site and the following samples were collected: water, sediment,
aquatic macroinvertebrates, vertebrates (fish and amphibian species), as well as noninvasive
tissue from birds (feathers). The physico-chemical characteristics of the water
were determined by measuring the chlorophyll-a concentrations, nutrient levels and
suspended solid content. The sediment was analysed for organic content, water content,
as well as sediment particle size distribution. The methylmercury concentrations in the
water, sediment and biotic components were determined through cold vapour atomic
fluorescence spectrometry, whilst inorganic mercury, cadmium, chromium, copper, lead,
manganese and uranium concentrations in these samples were determined through
inductively coupled plasma mass spectrometry. All analyses were subjected to
appropriate quality analysis and quality control procedures. The relationship between
environmental mercury exposure and biological effects was determined using changes in
the macroinvertebrate community assemblage structure as the biological endpoint. The
invertebrate samples were retained for enumeration and lower taxonomic identification in
the laboratory. Data were subjected to the appropriate univariate statistical analysis (oneway
ANOVA and regression), as well as multivariate statistical analyses (redundancy and
principal component) to study spatial and temporal trends in mercury distribution and
associated biological responses.