Diss. (sammanfattning) Stockholm : Univ., 2004. / Härtill 5 uppsatser.

M.Sc. / The study looks into the sediment-bound metals (Fe, Mn, Cu, Cr, Cd, Co, Pb, Ni, Zn and Hg) of the Leeu/Taaibospruit catchment, which is impacted by agricultural, industrial and urban development. A number of chemical procedures, including total metal determination, the Tessier-sequential extraction scheme, the BCR Protocol, evaluation of the % TOC and determination of AVS to SEM ratios were applied to sediment samples collected from eight sites along the two rivers in the study area. Samples were collected during both high flow (summer) and low flow (winter) conditions. Following the chemical characterisation, bioaccumulation testing was conducted by exposing chironomid larvae to the sediment samples collected in from the study sites and determining their metal uptake relative to control specimens in uncontaminated sediments. These bioaccumulation results were then considered in conjunction with the chemical parameters in an attempt to identify any trends and correlations. Significant spatial and temporal differences were found in the metal concentrations from the study area. The total extraction results indicated that abundant amounts of Cr and Fe are present throughout the system. This was expected based on the make-up of the underlying geology. In addition, one of the sites, which is in close proximity to the town of Sasolburg, was identified as a potentially contaminated site. This site had significantly higher concentrations of Zn, Cu, Pb and, most notably, Hg when compared to the other sites. The elevated metal concentrations are most evident in samples collected under low flow conditions, but are also seen in the high flow Hg concentrations. Sequential extractions showed that Fe and Cr are concentrated in the residual phases of the sediment. Copper is largely present in the oxidisable fraction under low flow conditions, but also has considerable residual and reducible chemical forms. Manganese and Zn are distributed among all the different chemical phases and are therefore likely to be readily available for uptake by benthic organisms. The TOC was found to be highest during low flow conditions and at those sites with observable amounts of organic debris from the surrounding reeds and other vegetation. The AVS/SEM ratios were used to predict that due to the formation of insoluble metal sulphides, Cd, Cu, Hg, Ni, Pb and Zn are unlikely to be bioavailable at certain sites, i.e. the contaminated site 1 and at site 5, which only has agricultural impacts. In general, the bioaccumulation of Fe, Co, Ni, Cr and Mn was higher in the test larvae than the control larvae. Bioaccumulation of Cu, Pb, Zn and Hg levels were only higher than the control worms at sites where contamination was suspected to have taken place. Average bioaccumulation factors indicated that Hg is the metal that is most readily available for bioaccumulation, followed by Cu, Zn and Mn. All of these metals were bioconcentrated in the tissues of the test chironomids, while levels of Fe, Ni, Cr and Pb were found to be lower in the organisms than in the sediments. Although many of the chemical fractions were found to correlate significantly with the uptake of the different metals, the best overall correlation existed between the bioaccumulated metal and the total non-residual fraction. In fact, the sum of the first four steps of the Tessier-scheme correlated significantly with the bioaccumulated metal for all elements considered in the calculation, except for Pb. Additionally, the predictions made by the AVS model were found to be useful in justifying the behaviour and accumulation patterns of Hg, Zn and Cu at certain sites. The correlations and bioavailability clearly differed spatially, temporally and among the different elements. It is therefore suggested that prediction of the bioavailability and subsequent uptake of sediment-bound metals will require as many chemical and environmental factors as possible, and should include bioaccumulation and toxicity testing in order to examine the validity and completeness of these predictions.

M.Sc. (Aquatic Health) / 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 rnacroinvertebrates, 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. This study showed that elevated concentrations of some nutrients and other dissolved solids were present in the system and that the water quality from the upper catchment of the Taaibosspruit (near the industries) had an impact on the downstream sites. The highest mercury concentrations were found at the sites closer to the industrial complex. These concentrations were higher than the concentrations from the reference site and when compared to international mercury guidelines, it was found to be too high. Comparison of the mercury concentrations in the water and sediment with environmental parameters also revealed that some of these parameters significantly influenced the environmental mercury concentrations. It was found that the biota has bioaccumulated mercury, which has resulted in the biomagnification of methylmercury by the biota from the different trophic levels of the ecosystem from this system. The results of the other six metals showed that the highest concentrations were found at the sites closer to the industries, with very high cadmium and copper concentrations in the water at the site where wastewater from the industries enters the system. These high concentrations in the water, suspended particles and sediment resulted in the accumulation of the metals by the biota present in this system. The sediment-dwelling Chironomidae-larvae bioaccumulated these metals to higher levels than the other biota from this system. The response of aquatic macroinvertebrates to high mercury exposure was dearly visible, as the sites where the environmental mercury concentrations were the highest, had low species richness. The environmental variables also influenced the community structure of the macroinvertebrates by reducing the number of different families at the more impacted sites. The results have shown that some of the fauna in the Taaibosspruit system were reduced in favour of the more tolerant families, namely Chironomidae and Oligochaeta. Thus, it was found that Taaibosspruit system is impacted upon by the surrounding industries, namely by enhancing the bioaccumulation of mercury, and influencing the macroinvertebrate community structure.