Radiocaesium activity concentrations in parmelioid lichens within a 60Â km radius of the Fukushima Dai-ichi Nuclear Power Plant

Radiocaesium activity concentrations (134Cs and 137Cs) were measured in parmelioid lichens collected within the Fukushima Prefecture approximately 2 y after the Fukushima Dai-ichi Nuclear Power Plant accident. A total of 44 samples consisting of nine species were collected at 16 points within a 60 km radius of the Fukushima Dai-ichi Nuclear Power Plant. The activity concentration of 134Cs ranged from 4.6 to 1000 kBq kg−1 and for 137Cs ranged from 7.6 to 1740 kBq kg−1. A significant positive correlation was found between the 137Cs activity concentration in lichens and the 137Cs deposition density on soil (n = 44), based on the calculated Spearman's rank correlation coefficients as r = 0.90 (P < 0.01). The two dominant species, Flavoparmelia caperata (n = 12) and Parmotrema clavuliferum (n = 11), showed strong positive correlations, for which the r values were calculated as 0.92 (P < 0.01) and 0.90 (P < 0.01) respectively. Therefore, Flavoparmelia caperata and Parmotrema clavuliferum are suggested as biomonitoring species for levels of radiocaesium fallout within the Fukushima Prefecture.