A comparison of programming notations for a tertiary level introductory programming course
- Authors: Cilliers, Charmain Barbara
- Date: 2004
- Subjects: Computer programming -- Study and teaching (Higher) -- South Africa , Computer programmers -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11093 , http://hdl.handle.net/10948/d1019679
- Description: Increasing pressure from national government to improve throughput at South African tertiary education institutions presents challenges to educators of introductory programming courses. In response, educators must adopt effective methods and strategies that encourage novice programmers to be successful in such courses. An approach that seeks to increase and maintain satisfactory throughput is the modification of the teaching model in these courses by adjusting presentation techniques. This thesis investigates the effect of integrating an experimental iconic programming notation and associated development environment with existing conventional textual technological support in the teaching model of a tertiary level introductory programming course. The investigation compares the performance achievement of novice programmers using only conventional textual technological support with that of novice programmers using the integrated iconic and conventional textual technological support. In preparation for the investigation, interpretation of existing knowledge on the behaviour of novice programmers while learning to program results in a novel framework of eight novice programmer requirements for technological support in an introductory programming course. This framework is applied in the examination of existing categories of technological support as well as in the design of new technological support for novice programmers learning to program. It thus provides information for the selection of existing and the design of new introductory programming technological support. The findings of the investigation suggest strong evidence that performance achievement of novice programmers in a tertiary level introductory programming course improves significantly with the inclusion of iconic technological support in the teaching model. The benefits are particularly evident in the portion of the novice programmer population who have been identified as being at risk of being successful in the course. Novice programmers identified as being at risk perform substantially better when using iconic technological support concurrently with conventional textual technological support than their equals who use only the latter form. Considerably more at risk novice programmers using the integrated form of technological support are in fact successful in the introductory programming course when compared with their counterparts who use conventional textual technological support only. The contributions of this thesis address deficiencies existing in current documented research. These contributions are primarily apparent in a number of distinct areas, namely: • formalisation of a novel framework of novice programmer requirements for technological support in an introductory programming course; • application of the framework as a formal evaluation technique; • application of the framework in the design of a visual iconic programming notation and development environment; • enhancement of existing empirical evidence and experimental research methodology typically applied to studies in programming; as well as • a proposal for a modified introductory programming course teaching model. The thesis has effectively applied substantial existing research on the cognitive model of the novice programmer as well as that on experimental technological support. The increase of throughput to a recommended rate of 75 percent in the tertiary level introductory programming course at the University of Port Elizabeth is attributed solely to the incorporation of iconic technological support in the teaching model of the course.
- Full Text:
- Date Issued: 2004
- Authors: Cilliers, Charmain Barbara
- Date: 2004
- Subjects: Computer programming -- Study and teaching (Higher) -- South Africa , Computer programmers -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11093 , http://hdl.handle.net/10948/d1019679
- Description: Increasing pressure from national government to improve throughput at South African tertiary education institutions presents challenges to educators of introductory programming courses. In response, educators must adopt effective methods and strategies that encourage novice programmers to be successful in such courses. An approach that seeks to increase and maintain satisfactory throughput is the modification of the teaching model in these courses by adjusting presentation techniques. This thesis investigates the effect of integrating an experimental iconic programming notation and associated development environment with existing conventional textual technological support in the teaching model of a tertiary level introductory programming course. The investigation compares the performance achievement of novice programmers using only conventional textual technological support with that of novice programmers using the integrated iconic and conventional textual technological support. In preparation for the investigation, interpretation of existing knowledge on the behaviour of novice programmers while learning to program results in a novel framework of eight novice programmer requirements for technological support in an introductory programming course. This framework is applied in the examination of existing categories of technological support as well as in the design of new technological support for novice programmers learning to program. It thus provides information for the selection of existing and the design of new introductory programming technological support. The findings of the investigation suggest strong evidence that performance achievement of novice programmers in a tertiary level introductory programming course improves significantly with the inclusion of iconic technological support in the teaching model. The benefits are particularly evident in the portion of the novice programmer population who have been identified as being at risk of being successful in the course. Novice programmers identified as being at risk perform substantially better when using iconic technological support concurrently with conventional textual technological support than their equals who use only the latter form. Considerably more at risk novice programmers using the integrated form of technological support are in fact successful in the introductory programming course when compared with their counterparts who use conventional textual technological support only. The contributions of this thesis address deficiencies existing in current documented research. These contributions are primarily apparent in a number of distinct areas, namely: • formalisation of a novel framework of novice programmer requirements for technological support in an introductory programming course; • application of the framework as a formal evaluation technique; • application of the framework in the design of a visual iconic programming notation and development environment; • enhancement of existing empirical evidence and experimental research methodology typically applied to studies in programming; as well as • a proposal for a modified introductory programming course teaching model. The thesis has effectively applied substantial existing research on the cognitive model of the novice programmer as well as that on experimental technological support. The increase of throughput to a recommended rate of 75 percent in the tertiary level introductory programming course at the University of Port Elizabeth is attributed solely to the incorporation of iconic technological support in the teaching model of the course.
- Full Text:
- Date Issued: 2004
The effects of selected proline-based cyclic dipeptides on growth and induction of apoptosis in cancer cells
- Authors: Brauns, Seth Clint Aron
- Date: 2004
- Subjects: Cyclic peptides , Antineoplastic agents -- Testing , Apoptosis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11088 , http://hdl.handle.net/10948/396 , Cyclic peptides , Antineoplastic agents -- Testing , Apoptosis
- Description: An increasing number of cyclic dipeptides (CDPs) have been shown to exhibit important biological activity including antifungal, antibacterial, anticonvulsant and immunomodulatory activity. Furthermore, some CDP derivatives have been shown to exhibit antitumour activity in vitro and in vivo. Several proline-based CDPs that exhibit biological activity have been detected in various processed foods and beverages. In the present study, the potential of seven proline-based CDPs to inhibit cancer cell growth was investigated in HT-29 (colon), HeLa (cervical), MCF-7 (breast) and WHCO3 (oesophageal) cancer cell lines. The CDPs used in this study were cyclo(Phe-Pro), cyclo(Tyr-Pro), cyclo(Gly-Pro), cyclo(Pro- Pro), cyclo(His-Pro), cyclo(Leu-Pro) and cyclo(Thr-Pro). The sulforhodamine B (SRB) cell growth assay was used in an initial screening phase to investigate the effects of the CDPs in HT-29, HeLa and MCF-7 cells. After exposing the cells to 10mM of the respective CDPs for 48 hours, the SRB assay results showed that only cyclo(Phe-Pro) exhibited more than 50% growth inhibition (p<0.01) in the three cell lines. The other CDPs showed comparatively marginal growth-inhibitory effects, except for cyclo(Tyr-Pro), which exhibited a pronounced effect in MCF-7 cells compared to HT-29 and HeLa cells. The MTT assay was used to confirm the SRB assay results for cyclo(Phe-Pro) and cyclo(Tyr-Pro), extending the investigation to the use of the fourth cell line WHCO3 and using a longer exposure time of 72 hours. The MTT assay demonstrated a dosedependent (0.008-10 mM) growth inhibition by cyclo(Phe-Pro) with an IC50 value of 4.04 ± 1.15 mM for HT-29 cells. Cyclo(Phe-Pro) was subsequently used to investigate whether the growth-inhibitory effects of this CDP were related to the induction of apoptosis in HT-29 cells. Hoechst 33342 staining showed that 5mM cyclo(Phe-Pro) induced characteristic chromatin condensation and nuclear fragmentation in 18.3 ± 2.8% (p<0.01) of HT-29 cells after 72 hours. Furthermore, annexin V binding revealed that HT-29 cells treated with 5 mM cyclo(Phe-Pro) displayed phosphatidylserine externalization after 48 hours. In addition, it was shown that 10 mM cyclo(Phe-Pro) induced poly(ADP-ribose)polymerase PARP cleavage, one of the hallmark events of apoptosis. The use of the broad-range caspase inhibitor Z-VAD-FMK, showed that this PARP cleavage was caspase-dependent, which in turn was confirmed by demonstrating an increase in caspase-3 activity (p<0.01) in cyclo(Phe- Pro)-treated HT-29 cells. In conclusion, these findings demonstrate that cyclo(Phe-Pro) inhibited the growth of HT- 29, MCF-7, HeLa and WHCO3 cells, and induced apoptosis in HT-29 colon cancer cells, suggesting the potential antitumour activity of cyclo(Phe-Pro)-related CDPs.
- Full Text:
- Date Issued: 2004
- Authors: Brauns, Seth Clint Aron
- Date: 2004
- Subjects: Cyclic peptides , Antineoplastic agents -- Testing , Apoptosis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11088 , http://hdl.handle.net/10948/396 , Cyclic peptides , Antineoplastic agents -- Testing , Apoptosis
- Description: An increasing number of cyclic dipeptides (CDPs) have been shown to exhibit important biological activity including antifungal, antibacterial, anticonvulsant and immunomodulatory activity. Furthermore, some CDP derivatives have been shown to exhibit antitumour activity in vitro and in vivo. Several proline-based CDPs that exhibit biological activity have been detected in various processed foods and beverages. In the present study, the potential of seven proline-based CDPs to inhibit cancer cell growth was investigated in HT-29 (colon), HeLa (cervical), MCF-7 (breast) and WHCO3 (oesophageal) cancer cell lines. The CDPs used in this study were cyclo(Phe-Pro), cyclo(Tyr-Pro), cyclo(Gly-Pro), cyclo(Pro- Pro), cyclo(His-Pro), cyclo(Leu-Pro) and cyclo(Thr-Pro). The sulforhodamine B (SRB) cell growth assay was used in an initial screening phase to investigate the effects of the CDPs in HT-29, HeLa and MCF-7 cells. After exposing the cells to 10mM of the respective CDPs for 48 hours, the SRB assay results showed that only cyclo(Phe-Pro) exhibited more than 50% growth inhibition (p<0.01) in the three cell lines. The other CDPs showed comparatively marginal growth-inhibitory effects, except for cyclo(Tyr-Pro), which exhibited a pronounced effect in MCF-7 cells compared to HT-29 and HeLa cells. The MTT assay was used to confirm the SRB assay results for cyclo(Phe-Pro) and cyclo(Tyr-Pro), extending the investigation to the use of the fourth cell line WHCO3 and using a longer exposure time of 72 hours. The MTT assay demonstrated a dosedependent (0.008-10 mM) growth inhibition by cyclo(Phe-Pro) with an IC50 value of 4.04 ± 1.15 mM for HT-29 cells. Cyclo(Phe-Pro) was subsequently used to investigate whether the growth-inhibitory effects of this CDP were related to the induction of apoptosis in HT-29 cells. Hoechst 33342 staining showed that 5mM cyclo(Phe-Pro) induced characteristic chromatin condensation and nuclear fragmentation in 18.3 ± 2.8% (p<0.01) of HT-29 cells after 72 hours. Furthermore, annexin V binding revealed that HT-29 cells treated with 5 mM cyclo(Phe-Pro) displayed phosphatidylserine externalization after 48 hours. In addition, it was shown that 10 mM cyclo(Phe-Pro) induced poly(ADP-ribose)polymerase PARP cleavage, one of the hallmark events of apoptosis. The use of the broad-range caspase inhibitor Z-VAD-FMK, showed that this PARP cleavage was caspase-dependent, which in turn was confirmed by demonstrating an increase in caspase-3 activity (p<0.01) in cyclo(Phe- Pro)-treated HT-29 cells. In conclusion, these findings demonstrate that cyclo(Phe-Pro) inhibited the growth of HT- 29, MCF-7, HeLa and WHCO3 cells, and induced apoptosis in HT-29 colon cancer cells, suggesting the potential antitumour activity of cyclo(Phe-Pro)-related CDPs.
- Full Text:
- Date Issued: 2004
On the mocvd growth of ZnO
- Authors: Pagni, Olivier Demeno
- Date: 2004
- Subjects: Zinc oxide thin films , Metal organic chemical vapor deposition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11075 , http://hdl.handle.net/10948/382 , Zinc oxide thin films , Metal organic chemical vapor deposition
- Description: Zinc oxide (ZnO) is a II-VI semiconductor material that offers tremendous potential as a light emitter in the blue-to-UV range. It has a wurtzite structure, and a direct band gap that can be tuned from 3.0 to 4.0 eV by alloying with Cd or Mg, respectively. In this work, ZnO thin films were grown by metalorganic chemical vapor deposition (MOCVD) on n-Si 2 ° off (100), amorphous glass, n-GaAs (100), and c-plane sapphire substrates. Diethyl zinc (DEZn) and tert-butanol (TBOH) were chosen as precursors. For the first time, Second Harmonic Generation Imaging was applied to the mapping of ZnO epilayers. The images obtained highlighted the polycrystalline character of the thin films, and provided insight as to the growth mode of ZnO on Si. The influence of substrate temperature on the structural properties of the epilayers was investigated by X-ray diffraction and optical microscopy. Grain sizes as high as 54 nm were measured. The optimum temperature range for this system proved to be 450 – 500 °C. The influence of the VI:II ratio during growth on the optical properties of the epilayers was studied by UV-vis-near IR spectroscopy. The lowest Urbach tail E0 parameter was measured for material grown at a VI:II ratio of 18:1. The films’ free electron concentration was shown to decrease by over two orders of magnitude, from 1019 to 1017 cm-3, as the VI:II ratio increased from 10 to 60:1. This decrease in carrier concentration with rising VI:II ratio was paralleled to the surge at 12 K of a photoluminescence (PL) emission band characteristic of p-type ZnO. The band gap energies extracted from room temperature transmission spectra ranged between 3.35 and 3.38 eV, in agreement with the value of 3.35 eV measured by room temperature PL. Moreover, variable temperature PL spectra were recorded between 12 and 298 K on ZnO grown on Si. The 12 K spectrum was dominated by a donor-bound exciton (D°X) at 3.36 eV, while the 298 K scan displayed strong free exciton emission (FX) at 3.29 eV. The width of the D°X band proved to be as narrow as 7 meV. The intensity ratio between the room temperature near-band edge emission and the defect-related green band was as high as 28:1, highlighting the optical quality of the layers deposited in this work. The electrical properties of the thin films were studied by Hall measurements (van der Pauw configuration), and a maximum room temperature mobility of 11 cm2/Vs was recorded. Furthermore, a palladium (Pd) Schottky barrier diode on ZnO was fabricated. The barrier height and ideality factor were calculated from current–voltage measurements to be 0.83 eV and 1.6, respectively. The capacitance–voltage curve of the diode yielded a carrier concentration in the depletion region of 8·1017 cm-3. This study has shown that the optical and electrical properties of ZnO depend strongly on the growth conditions employed. A suitable choice of growth parameters can yield high quality ZnO that may be used for various devices. Keywords: Hall, MOCVD, optical spectroscopy, photoluminescence, Schottky barrier diode, SH Imaging, X-ray diffraction, ZnO.
- Full Text:
- Date Issued: 2004
- Authors: Pagni, Olivier Demeno
- Date: 2004
- Subjects: Zinc oxide thin films , Metal organic chemical vapor deposition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11075 , http://hdl.handle.net/10948/382 , Zinc oxide thin films , Metal organic chemical vapor deposition
- Description: Zinc oxide (ZnO) is a II-VI semiconductor material that offers tremendous potential as a light emitter in the blue-to-UV range. It has a wurtzite structure, and a direct band gap that can be tuned from 3.0 to 4.0 eV by alloying with Cd or Mg, respectively. In this work, ZnO thin films were grown by metalorganic chemical vapor deposition (MOCVD) on n-Si 2 ° off (100), amorphous glass, n-GaAs (100), and c-plane sapphire substrates. Diethyl zinc (DEZn) and tert-butanol (TBOH) were chosen as precursors. For the first time, Second Harmonic Generation Imaging was applied to the mapping of ZnO epilayers. The images obtained highlighted the polycrystalline character of the thin films, and provided insight as to the growth mode of ZnO on Si. The influence of substrate temperature on the structural properties of the epilayers was investigated by X-ray diffraction and optical microscopy. Grain sizes as high as 54 nm were measured. The optimum temperature range for this system proved to be 450 – 500 °C. The influence of the VI:II ratio during growth on the optical properties of the epilayers was studied by UV-vis-near IR spectroscopy. The lowest Urbach tail E0 parameter was measured for material grown at a VI:II ratio of 18:1. The films’ free electron concentration was shown to decrease by over two orders of magnitude, from 1019 to 1017 cm-3, as the VI:II ratio increased from 10 to 60:1. This decrease in carrier concentration with rising VI:II ratio was paralleled to the surge at 12 K of a photoluminescence (PL) emission band characteristic of p-type ZnO. The band gap energies extracted from room temperature transmission spectra ranged between 3.35 and 3.38 eV, in agreement with the value of 3.35 eV measured by room temperature PL. Moreover, variable temperature PL spectra were recorded between 12 and 298 K on ZnO grown on Si. The 12 K spectrum was dominated by a donor-bound exciton (D°X) at 3.36 eV, while the 298 K scan displayed strong free exciton emission (FX) at 3.29 eV. The width of the D°X band proved to be as narrow as 7 meV. The intensity ratio between the room temperature near-band edge emission and the defect-related green band was as high as 28:1, highlighting the optical quality of the layers deposited in this work. The electrical properties of the thin films were studied by Hall measurements (van der Pauw configuration), and a maximum room temperature mobility of 11 cm2/Vs was recorded. Furthermore, a palladium (Pd) Schottky barrier diode on ZnO was fabricated. The barrier height and ideality factor were calculated from current–voltage measurements to be 0.83 eV and 1.6, respectively. The capacitance–voltage curve of the diode yielded a carrier concentration in the depletion region of 8·1017 cm-3. This study has shown that the optical and electrical properties of ZnO depend strongly on the growth conditions employed. A suitable choice of growth parameters can yield high quality ZnO that may be used for various devices. Keywords: Hall, MOCVD, optical spectroscopy, photoluminescence, Schottky barrier diode, SH Imaging, X-ray diffraction, ZnO.
- Full Text:
- Date Issued: 2004
The concentration of ten metals in the tissues of shark species Squalus megalops and Mustelus mustelus (Chondrichthyes) occuring along the Southeastern coast of South Africa
- Erasmus, Christina Petronella
- Authors: Erasmus, Christina Petronella
- Date: 2004
- Subjects: Sharks -- South Africa -- Effect of metals on. , Marine pollutio -- South Africa.
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11095 , http://hdl.handle.net/10948/d1019683
- Description: 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.
- Full Text:
- Date Issued: 2004
- Authors: Erasmus, Christina Petronella
- Date: 2004
- Subjects: Sharks -- South Africa -- Effect of metals on. , Marine pollutio -- South Africa.
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11095 , http://hdl.handle.net/10948/d1019683
- Description: 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.
- Full Text:
- Date Issued: 2004
The concentration of ten metals in the tissues of shark species Squalus megalops and Mustelus mustelus (chondrichthyes) occuring along the Southeastern coast of South Africa
- Erasmus, Christina Petronella
- Authors: Erasmus, Christina Petronella
- Date: 2004
- Subjects: Sharks -- South Africa -- Effect of metals on , Marine pollution -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11085 , http://hdl.handle.net/10948/328 , Sharks -- South Africa -- Effect of metals on , Marine pollution -- South Africa
- Description: 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.
- Full Text:
- Date Issued: 2004
- Authors: Erasmus, Christina Petronella
- Date: 2004
- Subjects: Sharks -- South Africa -- Effect of metals on , Marine pollution -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11085 , http://hdl.handle.net/10948/328 , Sharks -- South Africa -- Effect of metals on , Marine pollution -- South Africa
- Description: 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.
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- Date Issued: 2004
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