A pot-type water purifier captured 98% of the nonradioactive iodine and iodide when an ion-exchange resin and activated carbon were used. Approximately 93.8% of 131I, 74 to 84.5% of 134Cs, and 75 to 81.1% of 137Cs in rainwater were captured after six repeated purifications using the purifier. The remaining 6.2% of 131I was not removed by isotope exchange with nonradioactive I- or by reduction to I- using Na2S2O4. Approximately 19% of 131I, 40% of 134Cs, and 33% of 137Cs were adsorbed on the silica gel. Analysis of the removal rates of 73% for the mixed ion exchange resin, 59% for the silver ions, and 18% for the silver nanoparticle-bound clay indicated that the content of 131I adsorbed particles components was 23%. The concentration ratio of radioactive components in rainwater decreased from 5.9 to 1.4 upon ultrafiltration with a YM-1 membrane filter, indicating that a soft aggregation of the aerosol occurred. The IP and γ-ray spectrum analysis of the filter produced a cottonlike image of 131I. Analysis of the TEM image and its electron diffraction pattern indicated the aggregation of a small fraction of the SiO2 aerosol. The coagulation of radioactive components in rainwater using I-adsorbed SiO2 nanoparticles may be due to the exchange of the 131I isotope with I in I-SiO2 and the adsorption of 134Cs+ and 137Cs+ on the surface of SiO2 or the precipitation of the 131I-adsorbed aerosol and 134Cs- and 137Cs-adsorbed aerosols.
Approximately 19% of 131I was released in a solution mixing contaminated soil with distilled water and 10 wt% CaCl2 solution, and the remaining 131I tightly bound to the soil. Approximately 12 to 15% of the radioactive cesium was found in the supernatant after mixing with saturated KCl aqueous solution, and the repeated treatment for 1 day indicated the additional release of 11 to 15% in the supernatant. Approximately 15 to 20% of radioactive cesium was found in the supernatant by mixing with saturated KCl solution and KCl powder, followed by heating. The repeated treatment with 40% KI solution led to a maximum release rate of 66% of radioactive cesium from the soil.
The γ-rays of the atmospheric particles collected in Shizuoka-city from March 15 to March 27, 2011 were measured. Radioactive nuclides due to the Fukushima Daiichi Nuclear Power Plant accident were found in the samples. Day to day variation of concentration of 131I and 137Cs etc. indicated two times arrival of radioactive plume from Fukushima to Shizuoka-city and suggested that the surface of Shizuoka-city had been slightly contaminated with radioactive cesium on mainly March 15.
The removal rate of radioactive materials from contaminated water was experimentally obtained using various materials and commercial water purifiers with the aim of enabling the public to easily remove radioactive materials from rainwater and tap water contaminated by radioactive 131I, 134Cs, and 137Cs released by the Fukushima Daiichi Nuclear Power Plant accident using readily obtainable instruments and materials at home. Since it was difficult to obtain contaminated tap water, contaminated rainwater was used as samples in our experiments. In the rainwater, 131I, 132I, 134Cs, 137Cs, 132Te, 129mTe, and 129Te were detected. The abundance ratio of the isotopes depended on the location and date of collection, and the abundance of 131I was 12 to 26 times higher than that of 137Cs. Most of the radioactivity in the rainwater originated from 131I. The removal rate was obtained in the case of using readily available materials and water purifiers at home and in a university laboratory. The results of model experiments using nonradioactive I3- and radioactive 125I instead of 131I suggested that activated carbon was effective. On the basis of these results, we investigated the removal rates of radioactive iodine and cesium using five different pot-type water purifiers with activated carbon as the basic adsorbent, to which ion-exchange resin, a hollow fiber membrane, or a ceramic was added. Approximately 90 to 99% of 131I and 94 to 100% of 137Cs were removed by consecutive purifications using the pot-type water purifiers. These results indicated that these water purifiers can be easily used to remove 131I and 137Cs at home, although special care is required when boiling using an electric kettle because it causes the concentration of 131I. Faucet-mounted- and countertop-type water purifiers with activated carbon as the basic material are expected to have a similar performance to pot-type water purifiers, although this requires future experimental verification. We found that 1-9% of the radioactive 131I remained in the rainwater samples after repeated treatment with the pot-type commercial water purifiers, depending on the sampling location and time, and that some of the residual isotopes were adsorbed on silica nanoparticles. Furthermore, to improve the removal rate, it is necessary to develop a removal method for the remaining components.
Huge amounts of radioactivity derived from the Fukushima nuclear accident were scattered in the atmosphere. Various kinds of vegetables in three prefectures in the Tohoku area were contaminated with 131I and 137Cs over the legal limit for shipment. A simple and effective removal method for contaminated farm products was developed to ensure the relief of farmers and the security of consumers. Distribution imaging of radioactivity in the contaminated vegetables, the physical removal of radioactivity from contaminated vegetables and the chemical removal of radioactivity from contaminated vegetables were examined. As a result, there were two types of vegetable contamination, spot type or spread type. The concentration of radioactivity was higher on the outer side than the inner side of a vegetable leaf. More than 80% of radioactivity attaches to the surface of leaves. Radioactivity removal by water washing showed no significant difference between boiling water and cold water. There was no significant difference between hand-washing and running water washing. The radioactivity of vegetables decreased by 70-80% for 131I and more than 80% for 137Cs by reducing agent treatments. In particular, ascorbic acid is promising as a safe and versatile option.