Sources and variation of isotopic ratio of airborne radionuclides in Western Arctic lichens and mosses

This research concerned radioactivity of lichens and mosses from coastal zones of the Canadian Arctic and Alaska. Over 50 samples were collected from 7 positions during two scientific expeditions in 2012 and 2013. The tundra contamination caused by anthropogenic radionuclides was relatively low, reaching mean values with SD's of: 17.4 +/- 3.5 Bq/kg for Sr-90, 14.0 +/- 2.9 Bq/kg for Cs-134, 38.4 +/- 7.5 Bq/kg for Cs-137, 0.86 +/- 0.24 Bq/kg for Pu239+240, 0.065 +/- 0.017 Bq/kg for Pu-238 and 0.50 +/- 0.13 Bq/kg for Am-241. The increase of activity concentration with increasing latitudes was noticed mostly in regard to Sr-90, Pu isotopes and Am-241. The analysis of isotopic ratios exhibited dominant contribution of the global fallout (+SNAP 9A satellite re-entry fallout) for the presence of plutonium isotopes and Am-241. The Fukushima fallout signature was identified in a few lichens from Alaska. However, the influence of additional unknown factor on the occurrence of Sr-90 and Cs-137 has been detected in western part of Canadian Arctic. Natural radioisotopes of thorium and uranium were found throughout the entire investigated region and the average values of activity concentration with SD's were as follows: 2.92 +/- 0.47 Bq/kg for Th-230, 2.61 +/- 0.48 Bq/kg for Th-232, 4.32 +/- 0.80 Bq/kg for U-234 and 3.97 +/- 0.71 Bq/kg for U-238. Examined Western Arctic tundra was not affected with any technically enhanced natural radioactivity. (C) 2019 Elsevier Ltd. All rights reserved.