Abstract
The public concern about radiation protection of non-human species and environment is increasing. The development of an international framework for environmental radiation protection is encouraged by international organizations such as ICRP, UNSCEAR and IAEA. The purpose of environmental radiation protection is to conserve plants and animals, to maintain the diversity of species, the health and status of natural habitats. To achieve the purpose, the ICRP task group is developing a reference-animals-and-plants approach. This approach is useful for the estimation of the dose-response relationships at the individual level, but it may be difficult to estimate the effects of radiation on community and ecosystem levels by that approach because ecosystems consist of biotic and abiotic factors, where these factors can be organized into species, populations and communities. Ecosystems are really complicated systems. In addition to the reference-animals-and-plants approach, a holistic approach to the ecosystem is also necessary to ensure environmental radiation protection.
We have tried to assess the influence of ionizing radiation on ecosystem by adopting top-down approach. In the presentation, we describe the impact of ionizing radiation on microbial community in a paddy field and on the release of elements and ions from the paddy soil as an example. Although it is thought that bacteria are not sensitive to ionizing radiation exposure, the results of our study revealed that bacterial community structure, that is bacterial species compositions and the relative amount of each bacterial species, were influenced by a dose of about 5 Gy. In addition to the changes in the bacterial community structure, concentrations of sulfate and iron in the paddy water significantly increased and decreased, respectively. These results suggest that the functioning of the microbial ecosystem in the paddy field is influenced by radiation exposure.
