Studies were undertaken to measure genetic toxicity at the molecular and cytogenetic levels of biological organisation in marine invertebrates and flatfish. The responses in the early life stages and adult life stages of marine invertebrates (Mytilus edulis and Platynereis dumerilii) were measured following exposures to the physical agent ultraviolet radiation (UVR) and representative compounds of the chemical group, polycyclic aromatic hydrocarbons (PAHs) in laboratory conditions. Also, the potential changes of toxicity of PAH contaminants caused by interactive effects with UVR were evaluated. In a collaborative study with researchers at the Centre for Environment, Fisheries and Aquaculture Science (CEFAS), genotoxic measurements were carried out in marine flounder (Platichthys flesus) which had been chronically exposed in vivo to PAHs administered via their food in controlled laboratory conditions. Significantly elevated levels of DNA damage were only observed in fish exposed to the highest PAH concentrations. Dose-dependent cytogenetic responses were observed in the early life stages of both of the invertebrate species investigated following exposure to UVR. However, statistically significant increases in chromosomal aberration induction and sister chromatid exchange (SCE) induction, and decreases in proliferation rate index (PRI) and normal development were only observed at UVR levels exceeding that of equivalent environmentally realistic conditions, when related to historical and predicted ozone levels in the south west of England. The interactive effects of UVR and PAHs indicated that the genotoxic potential of PAHs is increased when photoactivation takes place, measured by increases in genotoxic responses in both the early and adult life stages. Following a series of laboratory studies, a field study was conducted whereby indigenous populations of marine invertebrates {Mytilus edulis and Cerastoderma edule) were used as target organisms. Haemolymph samples were collected from the animals and tested for genotoxic and cytotoxic effects, employing assays validated in the earlier laboratory studies. Correlations between samples showing high levels of DNA damage measured with the comet assay and sites with high levels of heavy metals in the sediments and soft tissue of the animals were established. Finally, an attempt was made to evaluate the DNA repair capabilities of haemocytes collected from M.edulis, A series of in vitro exposures were carried out using hydrogen peroxide (H2O2) an oxidising agent, and methyl methane sulfonate (MMS) an alkylating agent to induce DNA damage. These were incubated with cytosine β-D-arabino furanoside (AraC), to establish whether these cells had the capacity to repair DNA damage induced by the model chemicals. The results showed that DNA damage induced by H2O2 required DNA polymerases for repair, whereas MMS-induced damage and repair did not appear to be affected by the presence of AraC. In conclusion, the data collated from the research undertaken for this project showed that UVR and PAHs are able to induce genotoxic lesions measurable at the cytogenetic level and whole organism levels in early life stages; and at the molecular and cellular levels in the adult stages. The assays employed appeared to be useful for identifying potential "hotspots" for genotoxic agents in the environment as indicated by the results of the field study, however, the endpoints measured are not contaminant-specific and provide little information about the type of contaminant or agent which might be present. Nonetheless, it has been shown here that comet assay is applicable to different marine species (including Cerastoderma edule and Platichthys flesus) and it is a potentially useful method for detecting DNA damage as well as DNA repair.

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