Blooms of cyanobacteria have been known to cause illness in humans and death in wild and domestic animals. One of the toxins produced by cyanobacteria is microcystin, which is a potent hepatotoxin. Microcystin is taken up by bile acid transporters in the intestine and transported into the liver. After exposure to acute doses of microcystin, severe haemorrhage has been observed along with apoptotic and necrotic hepatocytes. The cytoskeletal structure of the hepatocytes is disrupted and oxidative stress is induced. Selenium, a known anti-oxidant, has been shown to induce increased activity of glutathione peroxidase. Glutathione peroxidase removes peroxides from cells protecting them from oxidative stress. This study set out to determine if selenium could play a role in preventing the damage to mice livers due to microcystin toxin. The protective role of selenium was explored in three main studies: in the first study, the ability of selenium to increase the survival time of mice exposed to a lethal dose of toxin was determined. In the second study the mice were exposed to sublethal chronic doses of toxin over 30 days. The ability of selenium to minimise liver damage under these conditions was determined. The final study investigated the mechanism of the protective effect of selenium. The results of the first study suggested that selenium could extend survival time. In the second study the selenium supplemented mice showed a reduction in the extent of the increase in liver weight and a decrease in the amount of lipid peroxidation induced compared to the mice that received only toxin. The histology of the selenium supplemented mice also showed a decrease in the severity and amount of morphological changes in the liver. The third study indicated that the protection shown by selenium might be mediated by an increase in the glutathione peroxidase (GPX) activity in selenium supplemented mice. This increase in GPX activity would increase the removal of the lipid hydroperoxides and prevent the damage they would cause in the cell. A further result indicated an increase in glutathione S-transferase in only the toxin control mice when compared to the selenium supplemented and control mice. ii In conclusion selenium offers protection against microcystin but further studies need to be done to provide statistically valid results to clarify the level of protection.

Selenium and tellurium do not occur to any great extent in Nature and they are seldom studied in any detail. However, a general understanding of their properties, both physical and chemical, is essential in an investigation of their analytical determination. A general account may be found in many of the text-books on inorganic chemistry, but the following resumè has been included in this dissertation for the sake of completeness.

Selenium has aroused much interest in the last decade. It is an essential trace element for man and animals and has been found to be the cofactor in two enzyme systems. The first, glutathionine peroxidase, acts as an anti-oxidant by destroying peroxides which attack cellular membranes. The second, iodothyronine 5'-deiodinase, converts thyroxine to triiodothyronine with the release of iodine. Selenium is obtained in the diet from plant and animal products and the amount present is dependent largely on the Se content and the chemical species present in local soils. Soils low in Se can lead to deficiency problems to the grazing ruminants, and have necessitated the use of Se fertilisers or direct Se injection into the livestock. The disposal of sewage sludge onto agricultural land will increase as new EC legislation comes into force in 1998. This may alleviate Se deficiency in soils or result in toxicity problems. The aims of this project were firstly to develop and validate a method to accurately measure Se in plants, soils and sewage sludges, examine which soil fractions Se was associated with and finally to study the uptake of Se by plants grown on sewage sludge amended soils. The Se concentration in samples was determined using isotope dilution - mass spectrometry by gas chromatography - mass spectrometry (GC-MS). This was the first application of the determination of Se in environmental samples and the use of a benchtop GC-MS for those analyses. Samples were spiked with 76-Se isotope solution. Plants were digested using nitric acid and hydrogen peroxide initially on a heating block and latterly by microwave oven digestion techniques. Soils and sewage sludges were digested using nitric acid and hydrofluoric acid. Selenium in the digests was reduced to Se(IV) and derivatised to 5'-nitropiazselenol. Validation of the methodology was achieved by the use of certified reference materials which gave results within the certified range with a low standard deviation. The Se content of four different freely drained acid Scottish soils under grasslands was in the range 0.5-0.8 mg-1 air dried soil and three sewage sludge samples contained between 1.1 and 3.5 mg g-1 dry matter. The ability of the digestion techniques to release organically bound Se as selenomethionine and selenocysteine was found to be around 100% efficient and the use of a microwave oven increased the number of samples which could be processed. A sequential extraction procedure was used to determine the soil fractions with which Se was associated. The four soils and the sewage sludge examined were all found to have less than 5% of the total Se available for plant uptake. The uptake of Se by plants grown in soils to which Se had been added as sodium selenate or sodium selenate was studied using both stable and radio isotopes of Se. Results obtained showed that the uptake of Se by plants grown in soils treated with selenite could be related to the soil characteristics, with ferric oxide levels, clay levels and organic matter content being the important factors. The uptake of Se by plants in the soils treated with selenate were less obviously related to soil properties but pH and P levels both appear to be important factors. Good reproducibility was obtained in all cases. Plants grown on sewage sludge amended soils were not found to contain measurable amounts of Se.

A series of compounds with the general formula R3PX2 and R3PX4 (where R = o-tolyl, m-tolyl, p-tolyl, o-anisyl, m-anisyl, p-anisyl, o-thioanisyl, p-thioanisyl, p-fluorophenyl, p-chlorophenyl, mesityl and X = Cl, Br, I) have been synthesised and studied by X-ray crystallography, multinuclear NMR spectroscopy and Raman spectroscopy. A study of the conformational features of the aryl groups in these structures was undertaken in order to investigate the role of steric effects and crystal packing on P-X and X-X bond lengths. Compounds with the general formula RSeX / RSeX3 (where R = p-fluorophenyl, p-chlorophenyl, p-bromophenyl, p-iodophenyl and X = Cl, Br, I) have been synthesised by reacting the diselenides with halogens in the stoichiometric ratios. The X-ray crystal structure of p-ClC₆H₄SeI.I₂ is the first crystallographically characterised example of a compound of stoichiometry RSeI₃, although it is better represented as an I₂ adduct of a Se(II) iodide than a Se(IV) compound. In contrast, (p-FC₆H₄)Se-Se(I)₂(p-FC₆H₄) is an I₂ adduct where the Se-Se bond has not been cleaved by iodine. Both structures are stabilised by weak Se...I and I...I interactions. p-FC₆H₄SeCl₃ is an example of a dimeric structure with bridging chlorines. [Ph₄PX] and Ph₃PX₂ were reacted with PhEX (where E = Se, Te and X = I, Br, Cl) to produce salts containing [PhEX₂]- and [PhEX₄] anions. Where possible all the products were then analysed via NMR and Raman spectroscopy and X-ray crystallography. The reactions of the ligand tris-p-fluorophenyl phosphine with sulfur and selenium are presented along with the subsequent reactions of these compounds with diiodine. All of the compounds are characterised via X-ray crystallography.

A ¹⁴C primary productivity bioassay was developed to detect selenium limitation in marine phytoplankton. Addition of Na₂Se0₃ to Se-deplete cultures of Thalassiosira pseudonana stimulated carbon uptake rates by up to 40%, when uptake was expressed on a per cell volume or relative basis. Recovery from Se-starvation was verified by changes in the growth rate and morphology of T. pseudonana. Carbon uptake rates of Katodinium rotundatum, grown in nutrient enriched artificial seawater supplemented with 10⁻¹⁰ M or 10⁻⁶ M Se, were unaffected by Na₂SeO₃ additions. Since Katodinium rotundatum did not exhibit growth responses to Se additions, it was concluded that 10⁻¹⁰ M Se was sufficient for the growth of this alga, which has not displayed an obligate Se requirement. Natural phytoplankton assemblages in the Strait of Georgia were examined for Se limitation with this ¹⁴C bioassay. Relative carbon uptake rates did not change following Na₂SeO₃ addition, indicating that these assemblages were not Se-limited at the time of the study. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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