Estimation of Cs isotope accumulation by litter, moss and grass in Lithuania attributed to the Fukushima Daiichi NPP accident

134Cs of the Fukushima-origin in biomonitors in Lithuania was used to compare the radionuclide accumulation efficiencies in different above-ground vegetation and litter to those in the surface of tree stumps. Samples of moss, the last year's perennial grass, litter under pine trees, as well as the surface layer of pine tree stumps cut down before the Fukushima Daiichi Nuclear Power Plant accident, were collected at a few sites in Lithuania in 2011-2012. Tree stumps served as a reference surface for the accumulation comparison. The comparative accumulation coefficient, estimated as a ratio of the total 134Cs deposition density in the samples of plants to that in the samples of tree stumps, related to the residual (fixed) fraction of 134Cs, was determined for grass, moss, and litter. This value exceeded unity for all groups of studied media. The obtained results for moss and litter were significantly higher; therefore, the use of moss and litter samples as biomonitors is more preferential than that of other species of above-ground vegetation after the radioactive accidents or non-radioactive events.