Retention characteristics of radiocaesium in lichens and their applicability as fall-out indicator

Dohi, Terumi   ; Omura, Yoshihito*; Fujiwara, Kenso ; Iijima, Kazuki  

Lichens are symbiotic organisms consisted of fungi and algae. A number of studies were carried out after the nuclear weapons tests and Chernobyl accident, and demonstrated that lichens were useful for indicator of radioactive fallout because they could take up large amount of radionuclides directly from their thallus due to lack of root system and retain them. However, in order to measure radiocaesium concentration in lichen, the lichen sample was collected from their habitat. Therefore, temporal change of radiocaesium concentration in same lichen individual has never reported. In addition, a retention of radiocaesium in lichens in Japan was unknown. The objective of this study is to investigate the temporal change of radiocaesium concentration in individual lichen. Lichen samples were parmelioid lichens which were grown on the trunk of Prunus spp. within Fukushima prefecture. The counting rate of surface of lichen was measured by using Geiger-Mueller (GM) survey meter with a lead collimator to evaluate the radiocaesium concentration. The contamination density in lichens increased from the initial measurement value after one year. It is considered that lichen may receive radiocaesium from stem flow including radiocaesium desorbed from canopy or stem.