A home water purifier was used to remove radioactive iodine and cesium from rainwater contaminated with the radioactive materials released by the Fukushima Daiichi Nuclear Power Plant accident following the earthquake and tsunami in 2011. To prevent internal radiation exposure, the rainwater was satisfactorily decontaminated by a simple method using the pitcher type water purifier, which is widely available to the general public. However, the results indicate that the ability for purification by the home water purifier will be reduced significantly if the water is not filtered by some method before the water purifier is used, especially in the case of natural water containing suspension matter.
The contamination of spinach collected immediately following the Fukushima Daiichi nuclear disaster was investigated. The radionuclides deposited in the spinach were 132Te, 131I, 132I, 134Cs, 136Cs and 137Cs. Only 40% of these radionuclides were removed when the spinach was washed with water or detergent. The two outside leaves of each spinach stump were contaminated with the radionuclides, but the three inside leaves were nearly uncontaminated. The most significant contamination was observed on the concavities, creases, veins and leaf or stem injuries of the spinach. Most of the radionuclides deposited on the surface, leading to a radioactivity concentration of the epidermal tissue 9 times that of the mesophyll tissue.
The internal doses of 372 persons who were dispatched to the Fukushima prefecture at any time from April 2011 to March 2012 were examined using a whole body counter within 2 months after they left Fukushima. 131I was only detected in April while 134Cs and 137Cs were found up to November 2011. The maximum committed effective dose and thyroid equivalent dose were 22.4 μSv and 0.4 mSv, respectively, which were observed in April 2011 by the scenario of acute inhalation. The internal radioactivity was found in persons staying in almost all of the interior and the coastal regions regardless of the distance from the Fukushima-Daiichi nuclear power plant. Although there was no statistical significance, the detection rate of 134Cs and 137Cs appeared higher in subjects dispatched for relatively long-terms. Comparison of internal doses evaluated by the whole body counter and by prediction from environmental radioactivity indicates that the intake of radioactivity in March, April and possibly May 2011, would be mainly attributable to the inhalation of airborne radioactive particles, whereas in June and later months ingestion of contaminated food would be the major route of radioactive intake. These results suggest that the risk for internal exposure existed for approximately six months after the radiological accident in almost the entire area of Fukushima, however, adverse health consequences by the radiation dose due to internal exposure seem to be negligible. Furthermore, the present risk for internal exposure is quite low in the normal living situation.
A new method was developed to estimate radioactive concentration [Bq/kg] using a portable dose rate meter [μSv/h] and a sample container surrounding the meter. It has been found that simple measurements can be performed for estimation of radioactive concentration. Lower limit of the detection (LOD) for the method was deduced to be 600 Bq under an environment of 0.057±0.005 μSv/h (3σ).
A huge amount of radioisotopes(RI), such as 132Te, 131I, 134Cs and 137Cs etc., was released into the atmosphere by the accident of Fukushima Daiichi nuclear power plant of Tokyo electric power company. According to the news immediately after the Fukushima nuclear accident, it was reported that almost all clothes were largely contaminated with the RI, confirmed by the early screenings of the general public evacuated from the Fukushima nuclear accident. On account of a worry about the RI contamination on clothes, many inhabitants could not dry their clothes out of doors in an area indicated the high radiation dose caused by the RI contamination in both Fukushima prefecture and some prefectures next to Fukushima prefecture even after the accidental release of RI was stopped from the accidental Fukushima nuclear power plant. In order to settle this situation effectively, the Ad Hoc Committee on Safety Measures against Radioactive Iodine and Cesium of the Japanese Society of Radiation Safety Management (JRSM) established a clothes analysis group. The Clothes Analysis Group aimed to analyze the actual RI contamination on clothes, and to develop a simple method to remove the RI by using washing machine sold on market, and so on. The results were summarized as follows; (1) The RI contamination was recognized obviously on clothes worn around the accidental Fukushima nuclear power plant immediately after the accident. However, on the clothes worn at July 2011, the RI contamination was not detected by a survey meter, but was detected a little by a Ge semiconductor detector. (2) The RI on clothes was decontaminated easily by a wash using a usual washing machine and detergent sold on the market. The RI decontamination ratios of the March clothes and the July one in 2011 were approximately 84 % after three times wash and 88 % after a once, respectively. (3) Radioactive Cs remained slightly after the wash and attached a little on clothes dried out of doors. Whenever the public lived in Fukushima prefecture might wear continuously the clothes contaminated by a trace of Cs after the wash and drying outside, the radiation safety was sufficiently confirmed because the estimated effective dose rate would be extremely lower than the annual dose limit. Consequently, the wash by using a commercial washing machine and detergent was useful and easy for removing the RI from clothes without a special apparatus for the RI decontamination. Furthermore, the wash was effective both for eliminating an anxiety over radiation exposure by wearing the contaminated clothes, and for bringing a feel of relief by wearing the clean washed clothes.
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