posted on 2015-12-17, 07:30authored byStefan Merz, Katsumi Shozugawa, Georg Steinhauser
In an unprecedented food monitoring
campaign for radionuclides,
the Japanese government took action to secure food safety after the
Fukushima nuclear accident (Mar. 11, 2011). In this work 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 a 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). Tap water was less contaminated;
any restrictions for tap water were canceled by April 1, 2011. 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.