Characteristics of radiocesium contaminations in mushrooms after the Fukushima nuclear accident: evaluation of the food monitoring data from March 2011 to March 2016.

The monitoring inspection of food after the Fukushima nuclear accident (2011) was essential for ensuring food safety in Japan and reducing the adverse health effects due to incorporation of inacceptable amounts of radionuclides, in particular radiocesium (134Cs and 137Cs). In this study, the mushroom fraction of the governmental data set of the first 5 years after the accident has been analyzed for contamination levels in mushrooms, in particular time trends and radioecological characteristics as well as associated health risks. The analyses show that mycorrhiza mushrooms are much more sensitive for radionuclide uptake than saprobiontic mushrooms (the latter of which include the very popular shiitake mushrooms (Lentinula edodes)). The maximum value reached 31,000 Bq/kg in a sample of apricot milkcaps in 2012. Analysis of the origin of the samples revealed that the origin (in terms of prefecture) of the mushrooms was a less determining factor for the contamination level than the type of mushrooms, as most exceedances in 2012 and thereafter were found outside Fukushima Prefecture. Several dose models were applied to the data to evaluate both worst case and realistic effective committed dose scenarios. The doses were generally rather low due to low consumption rates in the Japanese food basket. In any case, the analysis proved that the food monitoring campaign was highly effective in cutting doses to the public by more than a factor of 10 compared with a hypothetical scenario in which no monitoring had been conducted.