## 3 Results and Discussion
### Spatial Distribution of Anthropogenic Radionuclides
The variation between the outcomes from the current field studies and those of the airborne gamma survey can be explained by the instrumental peculiarities of the airborne gamma survey and the considerable waterlogging of the area, which makes it difficult to register gamma radiation from Cs-137 [47; 48; 49]. Figure 6 shows the spatial distribution plots of the pollution density of Am-241, Pu-238, and Pu-239+240. The nature of their distribution is not clear but is generally similar to that of Cs-137 and Sr-90. The pollution density of Am-241 ranges from 8.69 \(\times\) 10\({}^{-5}\) (3.22) Ci\(\times\)km\({}^{-2}\) (Bq\(\times\)m\({}^{-2}\)) to 1.11 \(\times\) 10\({}^{-3}\) (41.1) Ci\(\times\)km\({}^{-2}\) (Bq\(\times\)m\({}^{-2}\)), with an average of 4.36 \(\times\) 10\({}^{-4}\) (16.1) Ci\(\times\)km\({}^{-2}\) (Bq\(\times\)m\({}^{-2}\)). The pollution density of Pu-238 ranges from 1.84 \(\times\) 10\({}^{-5}\) (0.68) Ci\(\times\)km\({}^{-2}\) (Bq\(\times\)m\({}^{-2}\)) to 3.17 \(\times\) 10\({}^{-4}\) (11.7) Ci\(\times\)km\({}^{-2}\) (Bq\(\times\)m\({}^{-2}\)), with an average of 1.10 \(\times\) 10\({}^{-4}\) (4.07) Ci\(\times\)km\({}^{-2}\) (Bq\(\times\)m\({}^{-2}\)). The pollution density of Pu-239+240 ranges from 8.18 \(\times\) 10\({}^{-5}\) (3.03) Ci\(\times\)km\({}^{-2}\) (Bq\(\times\)m\({}^{-2}\)) to 4.04 \(\times\) 10\({}^{-3}\) (150.0) Ci\(\times\)km\({}^{-2}\) (Bq\(\times\)m\({}^{-2}\)), with an average of 1.08 \(\times\) 10\({}^{-3}\) (40.0) Ci\(\times\)km\({}^{-2}\) (Bq\(\times\)m\({}^{-2}\)). In several locations, these radionuclides were not detected as their measured values were below the MDA. Figure 5: Map of Cs-137 distribution in soils on the territory of the Nenets Autonomous Okrug (Northwest Russia, airborne gamma survey method, results refer to 1992) [46]. Figure 6: Am-241 (**a**), Pu-238 (**b**), Pu-239+240, (**c**) pollution density. As with Sr-90, Am-241, Pu-238, and Pu-239+240 have not been the subject of indepth research in the Nenets Autonomous Okrug. The estimated content of these radionuclides is found in the Mezenskiy and Primorskiy districts of the Arkhangelsk region. Thus, based on [24], the activities of Pu-239 and Pu-240 in organogenic soils within the Arkhangelsk region predominantly fall within the range of minimum measured activities up to 4 Bq\(\times\)kg\({}^{-1}\). In [24], the plutonium isotope content was determined by mass spectrometry, so Pu-239 and Pu-240 were measured separately. The activity of Am-241 does not surpass 3 Bq\(\times\)kg\({}^{-1}\). Comparable levels of these radionuclides can be observed in more northern regions, such as Svulbard, where Am-241 activity generally does not exceed 3-4 Bq\(\times\)kg\({}^{-1}\) but can reach up to 11 Bq\(\times\)kg\({}^{-1}\) in certain peat layers [23]. The activity of Pu-239+240 in Svulbard is predominantly within the range of up to 5-6 Bq\(\times\)kg\({}^{-1}\), with sporadic occurrences in certain layers where it reaches 23 Bq\(\times\)kg\({}^{-1}\). According to the results of isotopic ratios in [24] and [23], the main sources of radionuclide pollution are global atmospheric fallout and the Chernobyl accident. [PERSON] [24] also identifies tests carried out on the Novaya Zemlya archipelago as an additional source of pollution. The levels of plutonium and americium isotopes found in peat on the Kanin tundra are similar to those recorded in the Arkhangelsk region and on Spitsbergen Island (see Table S1). The activity of Am-241 in the Nes River basin territory does not surpass 1.4 \(\pm\) 0.7 Bq\(\times\)kg\({}^{-1}\), Pu-238--0.41 \(\pm\) 0.12 Bq\(\times\)kg\({}^{-1}\), Pu-239+240--3.4 \(\pm\) 0.6 Bq\(\times\)kg\({}^{-1}\).