The southeastern coast of South Africa is deemed unpolluted and with the exception of a few localized areas, is believed to be pristine. This study aimed to (1) assess the concentration of metals in the water and sharks (Squalus megalops, Mustelus mustelus) from different sites along the southeastern coast, (2) determine the effects that metals have on each other and investigate the accumulation and storage of metals in different shark tissues, (3) determine the effects of length and sex on metal concentration and the presence of metallothioneins in the liver. Metal concentrations in water from seven sites along the southeastern coast revealed concentrations below the detection limit of the extraction method, except for iron at St. Francis Bay which was below the recommended levels as supplied by DWAF. Met al concentrations in S. megalops from the seven sites revealed significantly elevated levels in individuals from Algoa and St. Francis Bay when compared to the other 5 sites. This was observed for all metals except manganese, which had a higher concentration at Cape Agulhas. After comparing the metal levels in muscle tissue (S. megalops) with data from the Department of Health it was concluded that the sharks caught at Algoa and St. Francis Bay were unsuited for human consumption. Liver and vertebral tissues from both S. megalops and M. mustelus were deemed unsuited for human consumption but further research should be conducted especially on vertebral metal concentrations. Comparing the metal concentration in different tissue types of S. megalops and M. mustelus significant difference were observed and attributed to differences in the maturity (thus age) of the two species. Significant differences in the metal concentration of males and females for both the species were observed. A higher number of differences were however observed in M. mustelus than in S. megalops, most probably due to the differences in maturity. Length and weight vs. metal concentration regressions in the males and females of both species revealed more negative than positive trends. This was found to be in accordance with other studies from around the world. Using the life stages of S. megalops, significant differences in the average concentration of metals were observed between the life stages, with embryos usually having the highest concentration. The metal concentration series determined for S. megalops were similar to that which have been reported in the literature in that iron and zinc occupied the highest concentration positions while cadmium, copper and manganese occupied the last three. The spleen usually had the highest metal concentration except for aluminium in skin and arsenic in muscle tissue. Pearson correlation revealed significant negative correlations between cadmium and the mentioned metals suggesting that cadmium replaces essential metals such as manganese, iron and copper as. Negative correlations between essential metals were observed most probably due to the competition for binding positions on ligands. Positive correlations were observed between metals in sp ecific tissue types and may be indicative of synergistic effects, e.g. aluminium may result in the accumulation of other metals such as cadmium. Positive and negative correlations between a specific metal and different tissue types have also been observed and it appears that there are movement of metals between tissue types. Positive correlation for essential metals between yolk and other tissue have been observed, although no correlations for non-essential metals were observed. This could potentially indicate a mechanism that prevents the accumulation of nonessential metals in embryos. Though no metallothioneins were isolated form the liver, the presence of cadmium in other proteins indicate that that cadmium is substituted for essential metals, and as this may result in deleterious physiological effects, further studies should be conducted. In conclusion it can be said that although some of the results were expected there are still quite a few unanswered question and further studies should be conducted.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nmmu/vital:11085 |
| Date | January 2004 |
| Creators | Erasmus, Christina Petronella |
| Publisher | University of Port Elizabeth, Faculty of Science |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Doctoral, PhD |
| Format | 350 pages, pdf |
| Rights | Nelson Mandela Metropolitan University |
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