Patterns in the spatial distribution of natural and man-made radionuclides in urban soils and bottom sediments of lakes of Monchegorsk

The article presents the results of radioecological studies in Monchegorsk city area (Murmansk Region). The aim was to identify the main patterns in the spatial distribution of natural and man-made radionuclides in urban soils and bottom sediments of lakes in the study area. Samples were collected across the city from the top 0–5 cm of soil as well as in the flare plume outside the city limits (68 samples). Sediment samples were taken from the top (0–5 cm) layer in lakes Lumbolka, Nyudyavr, Komsomolskoye, Imandra and Nyuduay (19 samples). Pedological, radiological, and mathematical statistics methods were used in the field and laboratory work. The values of the man-made 137 Cs specific activity were up to 31.3 Bq/kg in urban soil samples and up to 63.4 Bq/kg in soils within the industry impact zone. The values for natural radionuclides in soils were up to 14.2 Bq/kg in urban soils and up to 21.6 Bq/kg in the flare plume for 226 Ra, up to 18.3 Bq/kg in urban soils and up to 17 Bq/kg in the flare plume for 232 Th, up to 498 Bq/kg in urban soils and up to 317 Bq/kg in the flame plume for 40 K. In lake sediments, man-made 137 Cs amounted to 45.8 Bq/kg, and natural radionuclide levels were up to 62.6 Bq/kg for 226 Ra, 11 Bq/kg for 232 Th, and 268 Bq/kg for 40K. The spatial distribution of natural radionuclides in urban soils and lake sediments in Monchegorsk is undoubtedly influenced by the proximity of bedrock: gneisses, crystalline schists, granodiorites, diorites, diorite-gneisses. The distribution of 137 Cs was likely influenced by stratospheric fallout as a result of atmospheric nuclear tests, local fallouts upon tests at the Novaya Zemlya nuclear test site, and the underground nuclear explosions Dnepr-1 and Dnepr-2.