Radiocesium contamination of the moss Hypnum plumaeforme caused by the Fukushima Dai-ichi Nuclear Power Plant accident.

We investigated 134Cs and 137Cs activity concentrations in the common Japanese moss species Hypnum plumaeforme collected from 32 sites within ca. 100 km radius of the Fukushima Dai-ichi Nuclear Power Plant. A total of 32 samples of H. plumaeforme were collected during the field surveys from November 2013 to September 2014. The maximum radiocesium activity concentrations in H. plumaeforme were 60.9 ± 1.8 kBq kg-1 for 134Cs and 123 ± 2.3 kBq kg-1 for 137Cs. The mean value for the 134Cs/137Cs was 1.17 ± 0.05, and the mean Tag value was 0.09 ± 0.13. Positive correlations were obtained between total 134Cs + 137Cs activity concentrations in H. plumaeforme and the air dose rate with a correlation coefficient (r) of 0.55 (P = 0.001), and between 137Cs activity concentration in H. plumaeforme and 137Cs deposition density on soil with r of 0.55 (P = 0.001). These results suggest that the perennial moss species H. plumaeforme could be more suitable and useful as a qualitative indicator for the radiocesium pollution compared to vascular plants spreading over the lowlands including human habitation in Fukushima Prefecture.