Behavior of iodine in the soil-plant system

In order to understand the behaviour of radioactive and stable iodine in the environment, we have carried out radiotracer experiments and chemical analyses in the soil-plant systems. Parameters important for the assessment of radioiodine movement from the environment to man, e.g. soil-plant transfer factors for various agricultural crops and soil-solution distribution coefficient for different soils, were obtained. Mechanisms of iodine sorption and desorption on soil were also studied. Microorganisms and/or their products (e.g. enzymes) were found to play an important role in the fixation of iodine on soil. Iodine was observed to be desorbed from the flooded soils due to the reducing conditions (low Eh) created by the microbial activities. From the soil-rice plant system biogenesis methyl iodide was found to be evaporated into the atmosphere. Through experiment using 125I tracer, we found that volatile organic iodine was produced due to microbial activities (including bacterial activities)

Effects of acute gamma irradiation on soil invertebrates in laboratory tests

An understanding of the dose-effect relationships of ionising radiation for nonhuman biota establishes important baselines for the radiological protection of ecosystems. We used standard laboratory tests to examine the dose-effect relationships of gamma radiation on the survival, growth and reproduction of the earthworm, Eisenia fetida (Oligochaeta). Adult E. fetida were acutely irradiated with increasing doses of gamma radiation, and the subsequent survival, growth in wet weight and number of offspring were examined. The 50% lethal dose (LD50) was 825 Gy, and the 10% and 50% effective doses (ED10 and ED50) for growth were 20.2 and 94.7 Gy, respectively. The ED10 and ED50 for reproduction were 3.3 and 11.1 Gy, respectively

Derivation of regional hazardous doses for amphibians acutely exposed to ionising radiation

Estimation of 50% lethal doses from nuclear DNA contents and subsequent species sensitivity distribution analysis was performed to derive regional 5% hazardous doses (HD5) for major orders Anura (e.g., frogs) and Caudata (e.g., salamanders) of amphibians inhabiting Japan, Australia, France, Czech Republic, Canada and some US states, where nuclear power plants or uranium mines are located. The HD5 values ranged from 3.0 to 7.7 Gy for the Anura inhabiting there while they ranged from 2.9 to 4.6 Gy for the Caudata. Comparison of these results with the worldwide HD5s (5.3 Gy for the Anura and 3.3 Gy for the Caudata) suggests that benchmark values for the Asian and Oceanic Anura and the European Caudata can be set at higher doses than the global values. Regional differences should be, therefore, considered when benchmark values are derived for some taxonomic groups

Researches in National Institute of Radiological Sciences (NIRS) for radiation protection of non-human biota and ecosystems in Japanese environment

This paper summarizes research activities in National Institute of Radiological Sciences (NIRS) for evaluation of the radiation effects on selected terrestrial and aquatic organisms as well as the ecosystems. Seven organisms, conifers, fungi, earthworms, springtails, algae, daphnia and Medaka are presently selected to study. For the estimation of possible radiation dose, transfers of radionuclides and related elements from medium to organisms are evaluated. Dose-effect relationships of acute gamma radiation on the survival, growth, and reproduction of selected organisms have been studied. Studies on the effect of chronic gamma radiation at low dose rate were also started. In order to understand the mechanism of radiation effects and to find possible indicators of the effects, information of genome- and metagenome-wide gene expression has been collected. Evaluation of ecological effects of radiation is more challenging task. Study methods by using three-species microcosm were established, and an index for the holistic evaluation of effects on various ecological parameters was proposed. The microcosm has been simulated as a computer simulation code. Developments of more complicated and practical model ecosystems have been started. The Denaturant Gradient Gel Electrophoresis (DGGE) has been applied on soil bacterial community in order to evaluate the radiation effects on soil ecosystems