Uptake of Radiocesium by Hypha of Basidiomycetes : Radiotracer Experiments

Many papers 1−4 have reported high concentrations of radiocesium in mushrooms collected in Ukrainian and European forests after the Chernobyl accident. The concentrations of 137 Cs in forest mushrooms were markedly higher than those in autotrophic plants. 5 Mushrooms sometimes affect the behavior of Cs in the environment. 6 Lindner et al. 7 surveyed roe deer contamination with radiocesium isotopes in the rural prealpine area of Oberschwaben in southwestern Germany beginning in the autumn of 1986. They identified characteristic regional and seasonal patterns of contamination that resulted from its transfer from the soil to the grazing plants of these animals. They suggested that the periodic maximum observed in roe deer in the autumn was correlated with the mushroom season in the grazing forests. Since edible mushrooms for humans also have higher 137 Cs concentrations than other foodstuffs, they are important for an estimation of internal radiation doses from 137 Cs through foods. Skuterud et al. 8 reported dietary surveys and whole body monitoring at two sites in the Bryansk Region of the Russian Federation in order to estimate the transfer of Chernobyl radiocesium to humans. They found mushroom consumption was the predominant factor in a 60 – 70% mean increase in radiocesium activity concentrations in humans in the autumn. The contribution from a high concentration of 137 Cs in mushrooms was found worldwide because of atmospheric nuclear tests. In our most recent study, 9 the contribution of mushrooms to the total intake of 137 Cs in Japanese was estimated to be 28% (on average) of the total intake of 137 Cs, while that of 40 K was estimated to be only 1.9%. Gaso et al. 10 calculated the intake of 137 Cs through 30 local mushroom species collected from 1993 to 1999 in a semi-natural temperate forest in Mexico and found that the mushrooms contributed 37% of 137 Cs and 4% of 40 K to the total dietary intake of these contaminants. We suggest that it is unreliable to neglect 137 Cs in mushrooms when estimating internal doses of 137 Cs. Therefore, the accumulation behavior of radiocesium in mushrooms should be elucidated for understanding radiation protection and radioecology. Accumulation of radiocesium in fruit bodies has been observed by laboratory experiments. We carried out cultivation experiments for four basidiomycetes (Hebeloma vinosophyllum, Flammulina velutipes, Coprinus phlyctidosporus, and Agrocybe cylindracea) in a solid growth medium including 137 Cs as a radiotracer. 11, 12 Our results showed that fruit bodies of the four basidiomycetes accumulated Cs from the medium, although there were large differences in Cs concentration among mushroom species. 11 The effects of Cs in the medium on the accumulations by the fruit body of H. vinosophyllum were investigated, and it was found that the concentration ratios of 137 Cs were not highly influenced by coexisting Cs in the medium. 12