In-situ investigation of radioactive Cs mobility around litter zone in contaminated forest using spent mushroom substrata

We used the spent mushroom substrata (SMSs) which are a kind of by-product after growing edible mushrooms for the in-situ investigation of radioactive Cs mobility in litter zone in a forest of Fukushima prefecture, Japan. The powder SMS was filled in a plastic net bag of 0.35 × 0.55 m, then was placed in a forest for ~6 months under three kinds of different conditions without treatment (No treatment), covered with wooden box (With box), and with zeolite placed on upper position of ground surface (With zeolite). We determined the ratio of radioactivity (TF) in the SMS to that of the soil and litter beneath the SMS bags. TFs of ‘No treatment’ and of ‘With zeolite’ were determined between ~0.01 and ~0.05 for 6 months. On the other hand, TFs of ‘With box’ were lower by one order at 2 and 4 months than those of ‘No treatment’ and of ‘With zeolite,’ and nearly the same values as TFs of ‘No treatment’ and ‘With zeolite’ at 6 months. These results clearly indicate that radioactive Cs accumulates in SMS mainly by throughfall. In addition, for a period of several months, fungi contribute to the accumulation of radioactive Cs in the litter zone, even though radioactive Cs was tightly associated with the soil.