Tadaaki Ban-Nai

Daily intakes of 134Cs, 137Cs, 40K, 232Th, and 238U in Ukrainian adult males

Total diet samples were collected to estimate dietary intakes of several radionuclides for Ukrainian males by duplicate portion studies. The samples were collected in the Kiev, Rovno and Volynsky regions in autumn of 1994. Some foodstuffs, including milk and potato, were also collected in the same regions. Daily intakes of 232Th and 238U were estimated to be 2.0 mBq and 7.5 mBq per person, respectively. The estimated daily intake of 40K, 85 Bq per person, was equivalent to that of Reference Man (the intake of a West European and a North American). Daily intakes of 137Cs were found to be quite different between some regions. Daily intakes were 1.8 Bq per person in the Kiev region and 12 Bq per person in the Rovno and Volynsky regions. Daily intake of 134Cs was below 1 Bq per person.

Concentrations of 137Cs and 40K in edible mushrooms collected in Japan and radiation dose due to their consumption.

To estimate radiocesium intake due to eating mushrooms, about 100 samples belonging to 11 species were analyzed to establish representative values for 137Cs and 40K in common edible mushrooms available in food markets. Concentration ranges were <0.047-39 Bq kg(-1) (wet wt) for 137Cs and 30-210 Bq kg(-1) (wet wt) for 40K. The median concentrations were 1.3 Bq kg(-1) (wet wt) for 137Cs and 97 Bq kg(-1) (wet wt) for 40K. The 137Cs concentrations in cultivated mushrooms were markedly lower than those in wild mushrooms. The annual intake of 137Cs per person through mushrooms was calculated (using analytical results and food consumption data in Japan) to be 6.0 Bq for 137Cs, which is about 32% of the total dietary intake of this nuclide. The effective dose equivalent of 137Cs through mushroom was estimated to be 7.7 x 10(-8) Sv (range estimated from the standard deviation: 3.0 x 10(-8) - 2.0 x 10(-7)).

Transfer factors of radioactive Cs, Sr, Mn, Co and Zn from Japanese soils to root and leaf of radish.

Transfer factors (TFs) of some selected radionuclides from ten different Japanese soils to radish have been studied by radiotracer experiments. The geometric mean values of TFs (on a wet weight basis) of radioactive Cs, Sr, Co, Mn and Zn for edible parts of radish (tuber) were 0.0090. 0.029, 0.00094, 0.0034 and 0.067, respectively. TFs for leaf were higher than those for tuber. The geometric mean values of leaf/tuber ratios were 4.1 for Cs, 4.9 for Sr, 1.6 for Co, 11 for Mn and 1.9 for Zn. Most of the Cs TFs obtained for andosol, which is the most common arable soil in Japan, were higher than those for the other soils. This might be due to the high concentrations of organic matter and alophen in andosol. The obtained TFs were compared to reference values of IAEA Technical Report 364.

Transfer of some selected radionuclides (Cs, Sr, Mn, Co, Zn and Ce) from soil to root vegetables

Transfer of radionuclides from soil to root vegetables (radish, carrot and turnip) has been studied by radiotracer experiments using Andosol, a typical soil type in Japan. The averages of the transfer factors of137Cs,85Sr,60Co,54Mn and65Zn for edible parts of the three vegetables were 0.02, 0.14, 0.004, 0.09 and 0.13, respectively. The transfer factor of141Ce for the edible part of carrot was 0.0002. The transfer factors obtained for the edible part of root vegetables were markedly lower than those for leaf vegetables.

Radiotracer Experiments on Biological Volatilization of Organic Iodine from Coastal Seawaters

Biological volatilization of iodine from seawaters was studied using a radiotracer technique. Seawater samples were incubated aerobically in serum bottles with radioactive iodide tracer (125I), and volatile organic and inorganic iodine were collected with activated charcoal and silver wool trap, respectively. Iodine was volatilized mainly as organic iodine, and inorganic iodine volatilization was not observed. Influence of light intensity on the volatilization was determined, but no significant differences were observed under light (70,000 lux) and dark conditions. The effect of the chemical form of iodine on the volatilization was determined, and the results suggested that volatilization preferentially occurs from iodide (I−) but not from iodate (IO3 −). Volatilization did not occur when the samples were autoclaved or filtered through a 0.22-μm pore size membrane filter. Incubation of the samples with antibiotics caused decreased volatilization. Conversely, enhanced volatilization was observed when the samples were incubated with yeast extract. Fifty-nine marine bacterial strains were then randomly isolated from marine environments, and their iodine-volatilizing capacities were determined. Among these, 19 strains exhibited significant capacities for volatilizing iodine. 16S ribosomal RNA gene comparisons indicated that these bacteria are members of Proteobacteria (α and γ subdivisions) and Cytophaga-Flexibacter-Bacteroides group. One of the strains, strain C-19, volatilized 1 to 2% of total iodine during cultivation, and the gaseous organic iodine was identified as methyl iodide (CH3I). These results suggest that organic iodine volatilization from seawaters occurs biologically, and that marine bacteria participate in the process. Considering that volatile organic iodine emitted from the oceans causes atmospheric ozone destruction, biological iodine volatilization from seawater is of great importance. Our results also contribute to prediction of movement and diffusion of long-lived radioactive iodine (129I) in the environment.

Comparison of stable cesium and radiocesium on dietary intakes by Japanese subjects using 18 food categories

Dietary intakes of radiocesium and non-radioactive cesium in Japanese were estimated using a market basket study and found to be 61 mBq and 9.1 ng per person per day, respectively. Food categories having higher Cs contents (per g-fresh) were found to be as follows: mushrooms 35.9 ng; nuts and seeds 33.6 ng; meats 26.8 ng; fishes and shellfishes 21.6 ng; potatoes 19.2 ng; seaweeds 10.2 ng; and milk and milk products 7.19 ng. For137Cs, higher contents (per kg-fresh) were as follows: mushrooms 1.7 Bq; nuts and seeds 0.23 Bq; fishes and shellfishes 0.16 Bq; meats 0.13 Bq; potatoes 0.11 Bq; seaweeds 0.092 Bq; and milk and milk products 0.089 Bq. Distributions of stable cesium in the 18 food categories were similar to those of radiocesium.

Levels of radionuclides in plant samples collected around the uranium conversion facility following the criticality accident in Tokai-mura.

Abstract Concentrations of artificial radionuclides in plant samples collected in the surrounding areas of the uranium conversion facility of JCO Company Limited were studied following the criticality accident in Tokai-mura. Radionuclides detected in plants were 131 I , 133 I , 140 Ba - 140 La and 137 Cs . The highest concentrations of the nuclides were found in samples collected near the facility or its ventilation exhaust and the concentrations decreased sharply with distance. The origins of 140 Ba - 140 La and 137 Cs were thought to be from 140 Xe and 137 Xe , respectively, which were produced in the fission event and released to the atmosphere. The average 131 I / 133 I activity ratio was about 21 (decay-corrected to the end of fission). Levels of the radionuclides in plants outside the JCO grounds were markedly below the intervention levels for foodstuffs in Japan.

The JCO criticality accident at Tokai-mura, Japan: An overview of the sampling campaign and preliminary results

A criticality accident occurred on September 30, 1999 at the uranium conversion facility of the JCO Company Ltd. in Tokai-mura, Japan. A collaborating scientific investigation team was organized in two groups, the first to carry out research on the environmental impact (the environmental research group) and the second to assess the radiation effects on residents (the biological research group). This report concerns only the activities of the environmental research group. Four investigative teams were sent on different dates to the accident site and its vicinity to collect samples. About 400 samples were collected and subjected to analysis. An outline of the sampling campaign is presented here along with a brief chronology of the accident and the preliminary key results obtained by the independent research group are summarised in this Special Issue of the Journal of Environmental Radioactivity.

Residual neutron-induced radionuclides in a soil sample collected in the vicinity of the criticality accident site in Tokai-mura, Japan: A Progress Report

Abstract Residual neutron-induced radionuclides were measured in a soil sample collected in the vicinity of the location where a criticality accident occurred (in Tokai-mura, from 30 September to 1 October, 1999). Concentrations of 24 Na , 140 La , 122 Sb , 59 Fe , 124 Sb , 46 Sc , 65 Zn , 134 Cs and 60 Co in the soil sample were determined by γ-ray spectrometry, and neutron activation analysis was carried out for selected target elements in the sample. Tentative estimates of the apparent thermal and epithermal neutron fluences which reached the sample were obtained through combined analyses of 59 Fe / 58 Fe , 124 Sb / 123 Sb , 46 Sc / 45 Sc , 65 Zn / 64 Zn , 134 Cs / 133 Cs and 60 Co / 59 Co .

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

Derivation of effect benchmark values for each taxonomic group, which has been difficult due to lack of experimental effects data, is required for more adequate protection of the environment from ionising radiation. Estimation of effects doses from nuclear DNA mass and subsequent species sensitivity distribution (SSD) analysis were proposed as a method for such a derivation in acute irradiation situations for assumed nuclear accident scenarios. As a case study, 5% hazardous doses (HD₅s), at which only 5% of species are acutely affected at 50% or higher lethality, were estimated on a global scale. After nuclear DNA mass data were obtained from a database, 50% lethal doses (LD₅₀s) for 4.8 and 36% of the global Anura and Caudata species, respectively, were estimated by correlative equations between nuclear DNA mass and LD₅₀s. Differences between estimated and experimental LD₅₀s were within a factor of three. The HD₅s obtained by the SSD analysis of these estimated LD₅₀s data were 5.0 and 3.1 Gy for Anura and Caudata, respectively. This approach was also applied to the derivation of regional HD₅s. The respective HD₅s were 6.5 and 3.2 Gy for Anura and Caudata inhabiting Japan. This HD₅ value for the Japanese Anura was significantly higher than the global value, while Caudata had no significant difference in global and Japanese HD₅s. These results suggest that this approach is also useful for derivation of regional benchmark values, some of which are likely different from the global values.