Update on Radiation Monitoring Fukushima (29 March 2011, 16:30 UTC)

No significant changes were reported in the 45 prefectures in gamma dose rates compared to yesterday.

As of 28 March information on radioactivity in drinking water collected mainly from the Japanese Ministry of Health, Labour and Welfare indicates that recommendations for restrictions based on I-131 concentration remain in place only in four locations in the prefecture of Fukushima. To date, no recommendations for restrictions have been made based on Cs-137. The Japanese limits for the ingestion of drinking water by infants is 100 becquerel per litre.

Five soil samples, collected at distances between 500 and 1 000 metres from the exhaust stack of Unit 1 and 2 of the Fukushima Nuclear Power Plant on 21 and 22 March, were analysed for plutonium-238 and for the sum of plutonium-239 and plutonium-240. (Due to analytical reasons, the isotopes plutonium-239 and plutonium-240 cannot be measured separately). Plutonium-238 was detected in 2 of the 5 samples, while plutonium-239/240 was detected in all samples as expected.

Concentrations reported for both, plutonium-238 and plutonium-239/240 are similar to those deposited in Japan as a result of the testing of nuclear weapons. The ratio of the concentrations of plutonium-238 and plutonium-239/240 in two of the samples indicate that very small amounts of plutonium might have been released during the Fukushima accident, but this requires to be further clarified.

As far as food contamination is concerned, 63 samples taken from 24 – 29 March, and reported on from 27 – 29 March, for various vegetables, fruit (strawberries), mushrooms, eggs, seafood and pasteurized milk in eight prefectures (Chiba, Fukushima, Gunma, Ibaraki, Miyagi, Niigata, Tochigi and Yamagata), stated that results for iodine-131, caesium-134 and caesium-137 were either not detected or were below the regulation values set by the Japanese authorities.