Estimation of the Amount of ¹³⁷Cs Transferred into the Fruiting Bodies Considering Distribution of That of Shiitake Mushroom Logs

Abstract

In order to manage log-based shiitake cultivation which maintains radioactivity within the set acceptable level for food, it is important to know how much radiocesium is transferred from the bed-logs into the fruiting bodies. The amount of ¹³⁷Cs transferred from the bed-logs into the fruiting bodies was investigated by using konara oak (Quercus serrata) as the logs, which had fallen down in Fukushima Prefecture from April 2018 to December 2020. Statistical analysis showed significant relationships between the amount of 137Cs in the fruiting bodies and the amount of ¹³⁷Cs in the inner bark and the sapwood. Therefore, it is suggested that ¹³⁷Cs is transferred into the fruiting bodies from the inner bark and the sapwood. The statistical analysis also showed a significant relationship between the amount of ¹³⁷Cs in the fruiting bodies and the ratio of the amount of ¹³⁷Cs in the outer bark to the amount of ¹³⁷Cs in the whole logs (outer bark contamination rate), such that the amount of ¹³⁷Cs in the fruiting bodies increased as the outer bark contamination rate decreased. It is probable that ¹³⁷Cs, which was deposited on the outer bark during the early stages of the Fukushima Daiichi Nuclear Power Plant accident, was difficult to elute, increased the contamination rate of the outer bark. It is suggested that the initially deposited ¹³⁷Cs may be difficult to transfer to the fruiting bodies.