Factors affecting the cesium transfer factor to shiitake (Lentinula edodes) cultivated in sawdust medium

Abstract The transfer factor (TF) of radioactive cesium-137 ( 137 Cs) to shiitake ( Lentinula edodes ) cultivated on bed logs varies greatly. Therefore, the present study investigated which factors affect the TF using stable cesium-133 ( 133 Cs) and sawdust medium with 5% rice bran as a model, which had similar 133 Cs TFs to bed-log cultivation. It was found that the Cs concentration and nutrient concentration (represented by the nitrogen concentration) concerned with the TF in the model sawdust medium. In addition, the TFs calculated using total 137 Cs and 133 Cs concentrations differed in both bed-log cultivation and the model sawdust medium cultivation, while the TFs calculated using exchangeable 137 Cs and 133 Cs concentrations were the same in sawdust medium cultivation, indicating that exchangeable Cs in the medium is the source of Cs for the fruiting body and the former difference was due to the presence of other chemical speciation of Cs that could not be absorbed. One purpose of the TF on the mushroom farm is to determine the fruiting body 137 Cs concentration at the start of bed-log cultivation, therefore the prediction method of TF are discussed considering the future changes of 137 Cs concentrations in trees.