Migration of 238 U and 226 Ra Radionuclides in Technogenic Permafrost Taiga Landscapes of Southern Yakutia, Russia

• Published in: Water
• Main Authors: Aleksandr Chevychelov, Petr Sobakin, Aleksey Gorokhov, Lubov Kuznetsova, Aleksey Alekseev
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2021
• Subjects: cryolithozone; technogenic landscapes; radionuclides 238 U; 226 Ra; migration; content; Hydraulic engineering; TC1-978; Water supply for domestic and industrial purposes; TD201-500; permafrost; taiga; Yakutia
• Online Access: https://doi.org/10.3390/w13070966; https://doaj.org/article/248c8089822d4f7184c3ae4ca28deddb

This article describes the features and migration patterns of natural long-lived heavy radionuclides 238 U and 226 Ra in the major components of the environment including rocks, river waters, soils, and vegetation of permafrost taiga landscapes of Southern Yakutia, which helped us to understand the scale and levels of their radioactive contamination. Different methods have been used in this study to determine the content of 238 U and 226 Ra in various samples, including gamma-ray spectrometry, X-ray spectroscopy, laser excited luminescence, and emanation method. It was determined that the main source of radioactive pollution of soil and vegetation cover, as well as surface waters in these technogenic landscapes, are the dumps of radioactive rock that were formed here as the result of geological exploration carried out in this area during the last third of the 20th century. The rocks studied were initially characterized by a coarse, mainly stony gravelly composition and contrasting radiation parameters, where the gamma radiation exposure rate varied between 1.71 and 16.7 µSv/h, and the contents of 238 U and 226 Ra were within the range 126–1620 mg/kg and 428–5508 × 10 −7 mg/kg, respectively, and the 226 Ra: 238 U ratio was 1.0. This ratio shifted later on from the equilibrium state towards the excess of either 238 U or 226 Ra, due to the processes of air, water, and biogenic migration. Two types of 238 U and 226 Ra radionuclides migration were observed in studied soils, namely aerotechnogenic and hydrotechnogenic, each of which results in a different intraprofile radionuclide distribution and different levels of radioactive contamination. In this study, we also identified plants capable of selective accumulation of certain radionuclides, including Siberian mountain ash (Sorbus sibiricus) , which selectively absorbs 226 Ra, and terrestrial green and aquatic mosses, which accumulate significant amounts of 238 U.