Radiocesium Uptake in Two Fungal Bed-cultivated Edible Mushroom Species in Forests in Fukushima, Japan

In Japan, mushrooms have long been valued as food resources, but the Fukushima nuclear accident disrupted production and shipment due to radiocesium contamination. 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 ranged from 0.04 to 0.89 {micro}Sv/h. Radiocesium concentrations (combined 137Cs and 134Cs, expressed as Bq/kg at 90% water content) in fruit bodies were 0.4-12 (mean 2.3) for Ly. decastes and 0.2-43 (mean 8.1) for Le. nuda. Both species remained below Japans food safety threshold of 100 Bq/kg, indicating that safe cultivation is feasible across broad areas. Uptake patterns differed: concentrations in Ly. decastes correlated with contamination in litter and multiple soil layers, whereas in Le. nuda it correlated only with litter contamination. These findings suggest that clean soil fills for Ly. decastes and clean litter covers for Le. nuda could serve as mitigation strategies tailored to each species. Aggregated transfer factors (2.76 x 10-5 m2/kg for Ly. decastes and 6.60 x 10-5 m2/kg for Le. nuda) were 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.