MARINE POLLUTION AND ECHINODERMS: A BIOMARKER STUDY INTEGRATING DIFFERENT LEVELS OF BIOLOGICAL ORGANISATION
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There is growing concern that the invertebrate lest organisms commonly employed in the field of aquatic ecotoxicology may not be sufficient to accurately screen for the possible deleterious effects of contaminants discharged into the marine environment. The use of echinoderms has been proposed to redress this problem, due to their ecological importance and their evolutionary closeness to the chordates. But to date, there is a paucity of data in the published literature which has utilised the adult stages of echinoderms in laboratory based toxicology studies. The present studies aimed to fill this lack of information. A suite of biomarkers which operated at different levels of biological organisation (sub-cellular, cellular and individual level) were identified for use with different echinoderm species (the common sea star, Asterias rubens, the purple sea urchin, Paracentrotus lividus and the common brittle star, Ophiothrix fragilis). These biomarkers used were micronucleus induction, the Comet assay, the modified Comet assay, phagocytosis, neutral red retention, clearance rate and righting time. Concurrent exposures showed that echinoderms were more sensitive to model contaminants than a commonly used sentinel ecotoxicological test species, namely the blue mussel, Mytilus edulis. These contaminants included: the reference toxicants hydrogen peroxide (Chapter 2) and methyl methanesulphonate (Chapter 3); a pharmaceutical, cyclophosphamide (Chapter 3); a polycyclic aromatic hydrocarbon. benzo(a)pyrene (Chapter 4) and a heavy metal, cadmium (Chapter 5). The results for all the exposures showed that the biomarkers which operated at the lower levels of biological organisation (i.e. at the subcellular level - namely the micronucleus and Comet assays) were the most sensitive at detecting the deleterious effects of the contaminants. But, interestingly, some strong correlations were found between these sub-cellular consequences and those that operated at higher levels of biological organisation (for example, between righting time and both micronucleus induction and Comet assay in Asterias rubens following cyclophosphamide exposure). Theses correlations suggest that biomarkers which operate at the whole organism level (namely righting time and clearance rate) may serve as rapid and accurate indicators of possible damage induced by xenobiotics in echinoderms and bivalve molluscs.
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