137Cs concentrations in foliose lichens within Tsukuba-city as a reflection of radioactive fallout from the Fukushima Dai-ichi Nuclear Power Plant accident

137Cs concentrations in ten species of foliose lichens collected within Tsukuba-city in August 2013 ranged from 1.7 to 35 kBq/kg. The relationships between 137Cs in two dominant species, Dirinaria applanata and Physcia orientalis, and the air dose rate (μSv/h) at the sampling sites were investigated. 137Cs in P. orientalis measured about 1 year after the Fukushima nuclear accident was correlated (r2 = 0.80) more closely with the air dose rate than those measured after about 2 years (r2 = 0.65), possibly demonstrating its continued value as a biomonitor to reflect ambient fall-out levels. In contrast, those of Dirinaria applanata were not correlated with the air dose rate in either year.