Concentrations of 137Cs and 40K in mushrooms consumed in Japan and radiation dose as a result of their dietary intake

Mushrooms are known to accumulate radiocesium. To estimate the intake of radiocesium through the eating of mushrooms, about 30 samples belonging to 4 commonly consumed species (Lentinula edodes, Hypsizigus marmoreus, Grifola frondosa, and Tricholoma matsutake), were analyzed for Cs-137 and K-40. The concentration ranges were 0.060-29 Bq kg(-1) (wet wt) for Cs-137 and 38-300 Bq kg(-1) (wet wt) for K-40. The geometric mean concentration for Cs-137 was 0.56 Bq kg(-1) (wet wt), and the mean concentration for K-40 was 92 Bq kg(-1) (wet wt). The Cs-137 concentrations in L. edodes cultivated in mushroom beds (sawdust-rice bran media) were lower than those cultivated on bed logs (natural wood with bark). The annual intake of Cs-137 per person through mushrooms was calculated, by using the current analytical results and food consumption data in Japan, to be 3.1 Bq for Cs-137, which is about 28% of the total dietary intake of this nuclide. The effective dose equivalent of Cs-137 through mushrooms was estimated to be 4.0 x 10(-8) Sv, which is about the half the value obtained in our previous study. The decrease of the Cs-137 intake through mushrooms is probably related to changes in cultivation methods in recent years, from the use of bed logs to mushroom beds.