Radiocesium uptake in two fungal bed-cultivated edible mushroom species in forests in Fukushima, Japan.

Mushrooms have long been valued as food resources, but past nuclear accidents disrupted production and shipment due to radiocesium contamination. After the Fukushima nuclear accident in 2011, limited knowledge has particularly hindered outdoor fungal bed cultivation. To address this, we conducted cultivation experiments with Lyophyllum decastes and Lepista nuda across 14 broad-leaved deciduous forest sites in Fukushima Prefecture. Air dose rates at 1-m height were 0.04-0.89 µSv/h. 137Cs concentrations (Bq/kg at 90% water content) in fruit bodies were 0.4-12 (mean 2.2) for Ly. decastes and 0.2-42 (mean 8.0) for Le. nuda. Both species remained below Japan's food safety threshold of 100 Bq/kg, indicating that outdoor fungal bed cultivation is feasible for the species across broad areas. Uptake patterns differed: concentrations in Ly. decastes correlated with contamination in litter and multiple soil layers, whereas in Le. nuda, they correlated with upper soil and leaf mold contamination. These findings imply that clean soil fills for Ly. decastes and clean litter covers for Le. nuda may partially serve as mitigation strategies tailored to each species. Aggregated transfer factors (2.72 × 10-5 m2/kg for Ly. decastes and 5.72 × 10-4 m2/kg for Le. nuda) were one order of magnitude lower than those reported for wild mushrooms. Overall, this study provides new insights into reducing radiocesium assimilation by cultivated mushrooms and supports the revival of outdoor fungal bed cultivation in contaminated landscapes.