Eggs/larval of freshwater fish (Danio rerio) were exposed to low dose rates of external gamma radiation (from 1 to 1000 mGy d(-1)) over a 20-day period, with the objective of testing the appropriateness of the 10 mGy d(-1) guideline suggested by the IAEA. The present study examines different endpoints, mortality and hatching time and success of embryos as well as the genotoxicity of γ-irradiations (after 48 h). The 20-day embryo-larval bioassay showed an enhanced larval resistance to starvation after chronic exposure to γ irradiation (from low 1 mGy d(-1) to high dose rate 1000 mGy d(-1)) and an acceleration in hatching time. Gamma irradiation led to increased genotoxic damage Ito zebrafish egg (40-50% DNA in tail in Comet assay) from the lowest dose rate (1 mGy d(-1)). Possible mechanisms of γ radiotoxicity and implications for radioprotection are discussed.
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