After the severe accident at the Fukushima-1 Nuclear Power Plant in March 2011, radioactive contamination of food has become a matter of serious concern in Japan. There is considerable information about radioactive iodine and cesium, but little is known about uranium contamination. We determined uranium content in spinach by the Japanese official method (Manual on Radiation Measurement of Food in Emergency Situations). In the preliminary study, we confirmed that the use of a microwave digestion system for preparing the test solution of spinach could shorten the testing time and give acceptable results. The manual recommends the use of two elements (Tl and Bi) as internal standards for measurement of uranium by ICP-MS. We found that Tl was more suitable than Bi to quantify trace amounts of uranium in spinach. However, it was necessary to determine Tl or Bi concentrations in the sample before analysis, since some samples of spinach contained significant amounts of these elements. The uranium contents of 9 spinach samples bought in April and May 2011 were less than 10 μg/kg, which are very low compared to the provisional regulatory limit in Japan.
The level of radioactive cesium (the sum of 134cesium (Cs) and 137Cs) was investigated in total diet samples collected from adults living in the Sapporo area, Hokkaido. They were ashed, and examined with a germanium semiconductor detector. The maximum and average radioactivities of cesium in an indivividual's daily food intake were as follows: 1.0 Bq and 0.24 Bq in July 2011, 1.3 Bq and 0.30 Bq in November 2011, 3.9 Bq and 1.0 Bq in February 2012, and 0.34 Bq and 0.12 Bq in July 2012, respectively. The committed effective dose would be 0.022 mSv/year in the case of continued intake of meals containing the maximum cesium concentration.
The concentrations of Pb-214 and Bi-214 in groundwaters and agricultural products from several geologically distinct parts of the Yamanashi region of Japan were measured and compared. The concentrations of Pb-214 and Bi-214 in groundwaters were well correlated with each other, and were consistent with the predominant geology in each area. The concentrations of both radio-nuclides in agricultural products were much lower than the levels in groundwaters, and did not appear to be related to local geology or habitat. Freshwater fish showed higher levels than agricultural products, though the levels were lower than those in groundwaters. Unexpectedly, wild mushrooms (but not cultivated mushrooms) showed relatively high levels of Bi-214, though their levels of Pb-214 were undetectable. Based on the levels of Pb-214 and Bi-214 detected here, annual internal radiation exposure of humans from these sources is considered to be extremely low.
Screening tests were carried out for radioactive cesium in foods using a NaI (Tl) scintillation survey meter. The screening level was set at 250 Bq/kg, and specimens exceeding this level were scheduled to be sent to an external testing organization, which would conduct further tests using a germanium semiconductor detector. Some specimens that did not reach the screening level were also sent to the same organization. Foodstuffs used in commercial food products circulated in Chiba city were targeted, along with food services provided to schools and day care centers. In all, 495 specimens were tested; however, no specimens exceeded the screening level. The results of verification tests confirmed that no specimen exceeded the tentative regulatory limit.
We surveyed foods on the market from areas that had been exposed to radioactive materials contamination following the Fukushima accident. We used a NaI (Tl) scintillation spectrometer for the screening tests and a germanium semiconductor detector for the final tests. Test results from 1,427 samples showed that 6 samples (0.4%) exceeded the regulatory limit of 500 Bq/kg. Considering the detection rate of radioactive cesium in each food category, we suggest that it is necessary to continue monitoring fruits such as chestnuts and ginkgo nuts, mushrooms (especially raw wood-shiitake), mountain vegetables, and sea fish.
Food samples were purchased in Nagoya based on daily intake in the Tokai region, and prepared as total diet samples according to the market basket method. The contents of radioactive cesium (Cs) were determined by using a γ-ray spectrometer with a germanium semiconductor detector, and a committed effective dose was estimated. Radioactive Cs was not detected in samples collected in 2006 before the Fukushima nuclear plant accident. Radioactive Cs was detected in samples prepared in August, 2011, five months after the accident. The sources were sugar and confectioneries (3rd food group), other vegetables, seaweeds and mushrooms (8th food group) and fishes, shellfishes and processed seafoods (10th food group). Only Cs-137 was detected in samples prepared in August, 2012, one year and five months after the accident. The sources were the 8th and the 10th food groups. The estimated committed effective dose for radioactive Cs was 0.0015 mSv in 2011 and 0.00016 mSv in 2012.
Following the Fukushima nuclear plant accident in Mar. 2011, the examination of radioactive contamination in foods is being carried out in Nagoya. During the period between 30 Mar. 2011 and 31 Oct. 2012, a total of 300 food samples were collected and the concentrations of radioactive nuclides were determined by means of γ-ray spectrometry using a high-purity germanium semiconductor detector. The results of analysis indicate that the concentrations of radioactive iodine (I) and cesium (Cs) were below the regulatory limits. Radioactive I (131I) was detected in 7 samples which belonged to the categories of green and yellow vegetables and other vegetables. Radioactive Cs (134Cs and 137Cs) was detected in 60 samples which belonged to the categories of rice and its processed products, potatoes and its processed products, nuts and seeds, green and yellow vegetables, other vegetables, fruits, mushrooms, fishes and shellfishes, processed sea foods, meat, milk and dairy products and other beverages.
Up to October 31, 2012, a total of 170 food samples marketed in Saitama Prefecture were examined following the setting of provisional regulatory limits for radioactivity in drinking water and foodstuffs by the Ministry of Health, Labour and Welfare on 1 April 2012. No sample exceeded the regulatory limits as determined by gamma ray spectrometry with a germanium semiconductor detector. However the radioactive cesium concentrations of food samples such as raw wood-shiitake and maccha (powdered green tea) produced in Saitama were nearly at the regulatory limits, being 74 Bq/kg and 84 Bq/kg, respectively.