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 (137)Cs and (40)K. The concentration ranges were 0.060-29 Bq kg(-1) (wet wt) for (137)Cs and 38-300 Bq kg(-1) (wet wt) for (40)K. The geometric mean concentration for (137)Cs was 0.56 Bq kg(-1) (wet wt), and the mean concentration for (40)K was 92 Bq kg(-1) (wet wt). The (137)Cs 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 (137)Cs per person through mushrooms was calculated, by using the current analytical results and food consumption data in Japan, to be 3.1 Bq for (137)Cs, which is about 28% of the total dietary intake of this nuclide. The effective dose equivalent of (137)Cs through mushrooms was estimated to be 4.0 currency 10(-8) Sv, which is about the half the value obtained in our previous study. The decrease of the (137)Cs intake through mushrooms is probably related to changes in cultivation methods in recent years, from the use of bed logs to mushroom beds.