Sources and pathways of artificial radionuclides to soils at a High Arctic site

Abstract

Activity concentrations, inventories and activity ratios of 137 Cs, 238 Pu, 239 + 240 Pu and 241 Am in soil profiles were surveyed in the dry tundra and the adjoining proglacial zones of glaciers at a High Arctic site on Svalbard. Vertical profiles of radionuclide activities were determined in up to 14-cm-thick soil sequences. Additionally, soil properties (pH, organic matter, texture, mineral composition and sorption capacity) were analyzed. Results obtained in this study revealed a large range of activity concentrations and inventories of the fallout radionuclides from the undetectable to the uncommonly high levels (inventories of 30,900 ± 940, 47 ± 6, 886 ± 80 and 296 ± 19 Bq/m 2 for 137 Cs, 238 Pu, 239 + 240 Pu and 241 Am, respectively) found in two profiles from the proglacial zone. Concentration of these initially airborne radionuclides in the proglacial zone soils is related to their accumulation in cryoconites that have a large ability to concentrate trace metals. The cryoconites develop on the surface of glaciers, and the material they accumulate is deposited on land surface after the glaciers retreat. The radionuclide inventories in the tundra soils, which effectively retain radionuclides due to high organic matter contents, were comparable to the global fallout deposition for this region of the world. The 238 Pu/ 239 + 240 Pu activity ratios for tundra soils suggested global fallout as the dominant source of Pu. The 238 Pu/ 239 + 240 Pu and 239 + 240 Pu/ 137 Cs activity ratios in the proglacial soils pointed to possible contributions of these radionuclides from other, unidentified sources.