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UBC Theses and Dissertations

Fish cell DNA repair and breakage assays for assessing aquatic genotoxicity Walton, Douglas G.


It is claimed that many cancers in man are causally related to chemical carcinogen exposure. Similarly epidemiological studies of fish populations have associated an elevated tumor incidence with environments contaminated with chemicals, some of which have demonstrated carcinogenic activity. Sampling and pathologically screening large numbers of fish is labour intensive, costly, time-consuming, and field studies provide only circumstantial evidence for an etiological agent. A variety of quick and inexpensive assays have been used with mammalian cells to detect probable carcinogenic activity by analyzing for DNA-damaging events. More recently fish cells and metabolizing enzymes are being used in these assays in order to provide tests with more relevance to the aquatic environment, validate mammalian test results, determine fish cell sensitivity to genotoxic agents, and, ultimately, to develop techniques to directly assess the genotoxic:carcinogenic potential of a particular environment. The present study initially compared the DNA repair response in fish and mammalian cells. Although the measured repair response of fish cells was found to be very low, in comparison to mammalian cells, the assay procedure was altered to increase the fish cell sensitivity. Despite being able to detect DNA repair in fish cells treated with 3,4-benzopyrene the repair technique was felt to lack the sensitivity necessary for in vivo monitoring. However, the low amount of repair measurable in fish cells suggested that tests for DNA breakage may be more sensitive. Subsequent comparative experimentation with the chromosome aberration and micronucleus tests confirmed this. Treatment of fish cells with 3,4-benzopyrene resulted in chromosome aberrations. Polycyclic aromatic hydrocarbons like 3,4-benzopyrene are important aquatic contaminants and have been found in elevated concentrations in sediments from Sturgeon Bank, an area near Vancouver at which a sewage treatment plant discharges. Field testing the developed genotoxicity techniques indicated cytotoxicity and chromosome aberrations, but no DNA repair, in cultured fish and mammalian cells exposed to Sturgeon Bank sediment extracts. However, in a parallel test, an in vivo increase in micronuclei frequency in starry flounder could not be demonstrated.

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