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 90Sr, 14.0 ± 2.9 Bq/kg for 134Cs, 38.4 ± 7.5 Bq/kg for 137Cs, 0.86 ± 0.24 Bq/kg for 239+240Pu, 0.065 ± 0.017 Bq/kg for 238Pu and 0.50 ± 0.13 Bq/kg for 241Am. The increase of activity concentration with increasing latitudes was noticed mostly in regard to 90Sr, Pu isotopes and 241Am. 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 241Am. The Fukushima fallout signature was identified in a few lichens from Alaska. However, the influence of additional unknown factor on the occurrence of 90Sr and 137Cs 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 230Th, 2.61 ± 0.48 Bq/kg for 232Th, 4.32 ± 0.80 Bq/kg for 234U and 3.97 ± 0.71 Bq/kg for 238U. Examined Western Arctic tundra was not affected with any technically enhanced natural radioactivity. •Study of wide spectrum of radioisotopes in Western Arctic tundra.•Increase of 90Sr, Pu isotopes and 241Am content with increasing latitude.•Nuclear weapon tests as the dominant source of Pu and Am.•Evidence of Fukushima fallout (134, 137Cs) in lichens from Alaska.•Unknown factor influencing 90Sr and 137Cs in the Canadian tundra.