M.Sc. / A lot of research in ecotoxicology is currently focused on identifying and developing suitable biomarkers for use in assessing the health of aquatic systems. Thus this study was done as part of a major project aimed at identifying and selecting suitable biomarkers to use in the Rietvlei System, South Africa. This study focused on the response of Clarias gariepinus (Burchell, 1822) to contaminants using three biomarkers: population genetic structure, DNA damage and metallothioneins (MT¡¦s). The main objectives of the study were to assess the potential of these biomarkers in C. gariepinus and to provide baseline data on the Rietvlei System. Eighteen enzyme loci (creatine kinase (Ck), esterase (Est), phosphoglucomutase (Pgm), glycerol-3-phosphate dehydrogenase (G3pdh-1 and -2), glucose-6-phosphatase isomerase (Gpi-A and -B), L-lactate dehydrogenase (Ldh-A and B), malate dehydrogenase (sMdh-1, -2 and -3), malate dehydrogenase (NADP+) (Mdhp), phosphogluconate dehydrogenase (Pgdh), isocitrate dehydrogenase (NADP+) (Idh); superoxide dismutase (Sod), and peptidase: substrate (leucyl tryrosine) (Pep-S1 and -2)) were screened for by horizontal starch gel electrophoresis. An agarose gel electrophoretic method was used for DNA damage determination and a spectrophotometric method for metallothionein. The Rietvlei System population (RSP) showed higher genetic variability as shown by the average number of alleles per locus (A), proportion of polymorphic loci (P) and expected average heterozygosity (HE) than the reference populations. Statistically significant deviations (p < 0.05) from Hardy-Weinberg proportions associated with heterozygote deficiencies occurred at Gpi-B, Idh, Pgdh, Ldh-A and Pep-S1 for RSP. These deviations could have been a result of small sample size. There was high genetic differentiation between RSP and the reference populations with FST values of 0.450 and 0.480 between RSP and wild population (WP) and RSP and Northern Cape population (NCP) respectively. A mean base-pair length of 6770.9 „b 10.68 (SE) bp was recorded in the Marais Dam population (MDP) that of 6327.2 „b 17.69 (SE) bp was recorded in the Rietvlei Dam population (RDP). The MDP had a higher proportion of DNA fragments with low base-pair lengths than RP indicating a higher level of DNA damage. The level of DNA damage in the MP was higher than in the RDP. The mean MT¡¦s content was 3.63 „b 0.643 (SE) nmol g-1 wet weight in the MDP and 4.35 „b 0.580 (SE) nmol g-1 wet weight in the RDP. There was no significant (p = 0.40) difference in the levels of MT¡¦s between the two dams. It was concluded that there were significant differences in genetic diversity between RSP and the other populations in unpolluted sites; hence genetic diversity in C. gariepinus has potential as biomarker of pollution. However, further research is recommended to investigate possible contributing factors to differences in genetic diversity such as inter-sex males, geographical isolation and differences in sample sizes used. DNA damage is also a potential biomarker provided due care is taken in interpreting average base-pair length data to consider differences in each DNA size class. It seems further research is required before conclusions are made about use of MT¡¦s as biomarker in this population. The levels of MT¡¦s in other uncontaminated systems will be useful to determine whether the levels recorded in this study are background levels or responses to contamination. / Prof. F.H. van der Bank

University of Macau / Institute of Chinese Medical Sciences

M.Sc. (Zoology) / Please refer to full text to view abstract

No description available.

Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 154-174.

Plots of field corn established in Michigan and Arizona were fertilized with two industrial wastes of nitric acid as nitrogen fertilizers. Major contaminants before processing (greater than 1000 mg/l) were Cu, Pb, Ti, Zn, and Zr. Of these, only Cu and Zn were present in significant quantities after neutralization with ammonium hydroxide. Application rates of 0, 67, 135, and 202 kg N/ ha were used, and compared with commercial ammonium nitrate fertilizer at 202 kg N/ ha. No significant differences were found in Pb, Zr, and Ti concentrations in corn tissue or grain due to treatments. Higher Cu and Zn levels occurred in plants from plots receiving the spent acids, but the concentrations were not significantly different from those found using commercial ammonium nitrate. No significant differences were found in corn grain Cu and Zn levels due to treatments.

No description available.

No description available.

M.Sc. / Aquatic toxicology is the qualitative and quantitative study of toxic effects of pollutants on aquatic organisms. The main goal in toxicity testing is to predict, in combination with other environmental factors, with known accuracy, a concentration of a specific toxicant that will not harm a system and to make this prediction in a responsible and cost effective manner. There are a variety of unique toxicity tests, with fish being one of the most popular organisms to work with, due to being the best-understood organism in the aquatic environment and its commercial importance. Zinc, copper and cadmium are three biologically important heavy metals that are commonly used in various industries. Low concentrations zinc and copper are essential micronutrients for both plants and animals, but in higher concentrations they become toxic to the environment and its biota. Cadmium has a chemical structure similar to that of zinc and is often found in association with it, but it is a very toxic substance. The effects of zinc, copper and cadmium on the free-embryo life stage (yolk sac phase) of Oreochromis mossambicus were examined, for evaluation as a possible ¡§early life stage¡¨ fish lethality assessment. ¡§Fish early life stage tests¡¨ are considered to be relatively quick, comparable and inexpensive screening tools for testing effluents and chemicals. The yolk-sac stage is considered the most sensitive life stage in fish. O. mossambicus free-embryos feed endogenously and are indigenous to southern Africa and are therefore a good choice for lethality testing. The effects of the same metals on randomly selected Culicidae (mosquito) larvae were also tested. The reason for randomly selected larvae was to determine the possibility of doing toxicity testing without a species-specific culture. Mosquitoes are very common and well known due to being vectors of various human diseases. Recommendations towards future studies, to determine the usefulness of both O. mossambicus embryos and Culicidae larvae as biological indicator organisms, were also looked at. / Prof. G.J. Steyn

M.Sc. / South Africa is a developing country in which the rapid increase in population size is accompanied by expanding mining and industrial sectors. All these factors have resulted in an increase in the demand for good quality water, but various anthropogenic activities continually result in pollution of the freshwater reserves in the country, via either diffuse or point sources. Metals resulting from both mining and industry are common pollutants of South African aquatic systems. Although some are essential elements that are necessary for normal growth and metabolism in organisms, all metals can become toxic at elevated levels, thus resulting in either lethal and sublethal effects. Aquatic organisms can also bioaccumulate metals thereby transferring them to their predators, including man. Monitoring of freshwater systems is thus necessary in order to protect the environment from these toxic substances, and ultimately to protect mankind. Most monitoring programmes should use an integrated approach in which both physico-chemical and biological aspects are monitored. The present study employed an integrated approach in order to investigate the state of metal pollution in two water bodies that are subjected to differential levels of metal contamination. Selected physico-chemical characteristics of the water and sediment were analysed, as were the levels of metals bioaccumulated by the Freshwater River crab, Potamonautes warreni. The specific object of this study was to assess the potential of P. warreni as a suitable bioaccumulative indicator of metal pollution in the aquatic environment. Water and sediment samples were collected from Germiston Lake and Potchefstroom Dam every alternate month between February 1995 and February 1996. Water quality data revealed that although the quality of the water at both sites was relatively high, Germiston Lake appeared to be more anthropogenically impacted than Potchefstroom Dam. Analysis of metal levels in the water and sediment indicated that while levels of copper, manganese, nickel, lead and zinc were higher in Germiston Lake, calcium and iron were present in higher concentrations in Potchefstroom Dam. Cadmium levels differed little between the two sites. With the exception of iron in Potchefstroom Dam, nickel in Germiston Lake, and zinc at both sites, all of the physical and chemical characteristics of the water from the two sites were within the boundaries of the South African guideline values laid down for the protection of aquatic life. Potamonautes warreni individuals were also collected every alternate month, and metal concentrations in these organisms were determined using atomic absorption spectrophotometry. The results of this investigation showed that metal levels in these organisms did tend to reflect those in the environment, with lower levels of calcium and iron and significantly higher (p < 0.05) levels of copper, manganese, lead, nickel, and zinc in P. warreni from Germiston Lake. Cadmium concentrations detected in these crabs were essentially the same at the two sites. All metals, except for cadmium, were influenced by the size of the crabs at one or other site, but never at both, thus suggesting that the presence of size-related trends is influenced by ambient metal levels in the system. Iron and lead concentrations in P. warreni from Potchefstroom Dam were the only metals that were influenced by the sex of the organisms, with higher levels found in female crabs. The results of the present study clearly indicate that metal levels in P. warreni are indicative of the environmental levels of metals to which these crabs are exposed since higher metal levels were found in the organisms from the site that had higher environmental metal levels. These organisms have proven to be useful bioaccumulative indicators of metal pollution in the aquatic environments from which they were captured, and they should therefore be incorporated into biomonitoring protocols. It must, however, be stressed that further research is required to increase our database on metal levels in these crabs from different aquatic systems.