Radiocaesium activity concentrations in parmelioid lichens within a 60 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. - Highlights: • ¹³⁴Cs and ¹³⁷Cs in 9 parmelioid lichen species in Fukushima Pref. were determined. • ¹³⁴Cs and ¹³⁷Cs in these species ranged 4.6–1000 and 7.6–1740 kBq kg⁻¹. • ¹³⁷Cs in these species was positively correlated with ¹³⁷Cs inventory in soil. • Flavoparmelia caperata and Parmotrema clavuliferum were dominated species. • Significant difference of ¹³⁷Cs accumulation level in the two species was observed