Evaluation of Radionuclide Induced Damage in Marine Invertebrates
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Limited studies have been carried out to assess the potential effects of ionising radiation on marine organisms. Therefore the general aims of this thesis were, (a) to assess the cytotoxic, genotoxic and developmental effects of ionising radiation on the embryo-larvae of two ecologically relevant marine invertebrates Mytilus edulis and Platynereis dumerilii, (2) to assess the effects of an environmentally relevant cocktail of radionuclides (3) to monitor the potential impact of radiation in the natural environment and finally (4) attempt to predict the potential effects of radiation at a population level. Following validation of developmental stages and mammalian based cytotoxic and genotoxic assays, chromosomal aberrations (Cabs), sister chromatid exchanges (SCEs) and proliferation rate index (PRI}, on the embryo-larvae of M. edulis and P.dumerilii, the embryo-larvae stages were exposed to a reference radionuclide, tritium, (0.37, 3.7, 37 & 370 kBq/ml). Low doses of radiation delivered by tritium were shown to be detrimental to the development of embryo-larvae with an increase in abnormality for P. dumerilii and an increase in mortality for M. edulis. Tritium increased the induction of chromosomal aberrations and sister chromatid exchanges, in exposed embryo-larvae, indicating that tritium is potentially genotoxic. Cytotoxic effects (reduction in the cell proliferation rate) were also observed following exposure of embryo-larvae to tritium. In collaboration with the Royal Devonport Dockyard (DML) investigations on the cytotoxic, genotoxic and developmental effects of a cocktail of radionuclides (radioactive liquid waste diluted to 1.8, 3.2, 5.6, 18%) were carried out. All embryo-larvae exposed to 18% radioactive waste were dead within 24h. Both species exhibited increased abnormality, SCEs and Cabs and a reduction in PRI in dilutions 1.8-5.6%. In general M. edulis appeared to be more sensitive to ionising radiation than P.dumerilii embryo-larvae. Following experiments on the embryo-larvae stages of the two marine invertebrates studies were carried out to assess the effects of ionising radiation on adult life stages. Following validation of mammalian based genotoxic assays (comet and micronucleus assays) on adult M. edulis, the mussels were exposed to a reference radionuclide, tritium, (0.37, 3.7, 37 & 370 kBq/ml) in an attempt to assess the genotoxic effects of ionising radiation on the adult life stage. An increase in the levels of single strand breaks (comet assay) and in the induction of micronuclei (micronucleus assay) in haemocyte cells was observed in adults exposed to tritium. In collaboration with the Royal Devonport Dockyard (DML) a field study was carried out to assess the use of the genotoxic assays (comet and micronucleus assays) as biomarkers of exposure to radiation in adult mussels transplanted to an area of radionuclide discharge. Statistical analysis detected no correlation between the health of the deployed mussels and the levels of environmentally realistic radioactivity. After development of P.dumerilii embryo-larvae to sexual maturity there appeared to be no affect on the number or sex of the worms that reached adulthood in comparison to control worms. Although at the highest concentration of tritium (370 kBq/ml) there was a reduction in the number of eggs produced from sexually matured females. In conclusion, from the current studies it can be stated that ionising radiation is cytotoxic and genotoxic to sensitive embryo-larvae stages of marine invertebrates. However further studies need to be carried out to correlate the effects seen at molecular levels with the potential long-term effects observed at population and community levels of these species.
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