抄録
We investigate the effect by radiation and the response to radiation using microorganisms which is useful to detect the effects at the level of population or community. Experiments using a microbial model ecosystem (microcosm) elucidated that the effects observed as an index of changes in the population density of microbes were detectable at the radiation dose of more than 50 Gy. The result was considered to be owing to the character of generally high radio-resistant microbes, but low dose of radiation is known to stimulate the growth rate of some kinds of microbes. When the effects of radiation are evaluated by the change in the population density of organisms, the stimulating effects will affect the evaluation, especially for the dose-response relationships at the dose range of threshold. It is therefore very important for determination of the threshold value to analyze the response to very low dose of radiation. From this point of view, we started the preliminary experiments to analyze the microbial response to very low-level dose rate of radiation, especially to elucidate the realities of stimulating effects. We report the results of experiments using Euglena and Paramecium exposed to gamma-rays at the dose rate of 0.5 mGy/day and hope to discuss the significance of this kinds of study for environmental radiation protection.
