Concentrations of radiocesium and potassium in basidiomycetes collected in Japan

Concentrations of 137Cs, 134Cs and 40K in about 60 mushroom samples (fruit bodies of basidiomycetes) belonging to 25 species collected in Japan have been studied. The levels of 137Cs varied very widely, ranging from less than 3 to 1520 Bq kg-1 (dry wt), while those of 40K were relatively constant. Concentrations of 137Cs in common edible mushrooms of Japan such as Lentinus edodes, Flammulina velutipes, Pleurotus ostreatus and Pholiota nameko were low (normally less than 50 Bq kg-1, dry wt). Concentrations of 134Cs in many samples were below the limit of detection (usually less than 5 Bq kg-1, dry wt). The median concentrations of 137Cs and 40K were 41 (dry wt) and 1150 Bq kg-1 (dry wt), respectively. From the 137Cs/40K ratios it was found that cesium rather than potassium was selectively taken up from the soils by fungi such as Suillus granulatus and Lactarius hatsudake. The 134Cs/137Cs ratios in mushrooms are related to the depth of the mycelium in the soil. The effective dose equivalent due to the dietary intake of radiocesium through mushrooms was estimated to be only 1.6 x 10(-7) Sv.