Blog Archive

Thursday, 5 February 2015

Analysis of Japanese Radionuclide Monitoring Data of Food Before and After the Fukushima Nuclear Accident

February 4, 2015
  1. The study reviewed foods testing for cesium 137 contamination and also strontium 90 contamination.
  2. Official assumptions had been than there was a set ratio of cesium 137 to strontium 90 across all foods.
  3. This is even more problematic as testing for actual strontium 90 in foods is done less often due to the complexity of the testing method.
  4. What was found is that over time the ratio of strontium 90 in foods had increased.
  5. A new study in the journal Environmental Science & Technology looked at governmental food testing in Japan.
In an unprecedented food monitoring campaign for radionuclides, the Japanese government took action to secure food safety after the Fukushima nuclear accident (11 March 2011). In this paper we analyze a part of the immense data set, in particular radiocesium contaminations in food from the first year after the accident. Activity concentrations in vegetables peaked immediately after the campaign had commenced, but they decreased quickly, so that by early summer 2011 only few samples exceeded the regulatory limits. Later, accumulating mushrooms and dried produce led to several exceedances of the limits again. Monitoring of meat started with significant delay, especially outside Fukushima prefecture. After a buildup period, contamination levels of meat peaked by July 2011 (beef). Levels then decreased quickly, but peaked again in September 2011, which was primarily due to boar meat (a known accumulator of radiocesium). Pre-Fukushima 137Cs and 90Sr levels (resulting from atmospheric nuclear explosions) in food were typically lower than 0.5 Bq/kg, whereby meat was typically higher in 137Cs, and vegetarian produce was usually higher in 90Sr. The correlation of background radiostrontium and radiocesium indicated that the regulatory assumption after the Fukushima accident of a maximum activity of 90Sr being 10% of the respective 137Cs concentrations may soon be at risk, as the 90Sr/137Cs ratio increases with time. This should be taken into account for the current Japanese food policy as the current regulation will soon underestimate the 90Sr content of Japanese foods.

Source: Environmental Science & Technology

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