Cs in lichens after the Fukushima Nuclear Accident

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

Large quantity of radionuclides, including Cs and Cs, were released into the atmosphere caused by the Fukushima Dai-chi Nuclear Power Plant (FDNPP) accident on March 11, 2011. As lichens are known to be effective tools to monitor environmental radioelements in both time and space, lichen samples are expected to be used to examine and monitor radiocaesium fallout from FDNPP in Japan. The purpose of this study is to discuss the estimation of radiocaesium fallout in the ecosystem based on the following examinations using lichens. Fifty-eight samples including foliose and fruticose lichens were collected from northern to central Japan especially focusing on Fukushima Prefecture during 2012 and 2013. After correction for radioactive decay (on each sampling date), the detected radiocaesium concentrations ranged from 16.1 Bq kg (d.w.) to 510,000 Bq kg for Cs and from 33.8 to 880,000 Bq kg for Cs in lichens. Cs concentration in the lichen samples generally increased with increase in the amount of fallout estimated by the Cs deposition in soil. The positive correlation was supported between Cs in lichens collected from Fukushima Prefecture and Cs inventories on soil calculated by Inverse Distance Weighted with Spearman's rank correlation coefficient (0.90, p 0.01). The activity ratios of Cs and Cs for the lichen samples ( = 44) collected within Fukushima Prefecture (decay corrected to March 11, 2011) were between 0.950.04 and 1.080.41. The ratios are consistent with those for radiocaesium derived from the FDNPP accident (reported as 0.89 to 1.2). The ratios obtained from lichen samples collected in outside of Fukushima Prefecture were 0.750.23 to 1.480.48. They were consistent with those from Fukushima. But one sample showing significantly small value, 0.480.16, might be influenced by different origin from Fukushima.