137Cs and isotopic ratios of Pu and U in lichens and mosses from Russian Arctic areas

Abstract

Knowledge of past anthropogenic sources of radionuclide contamination in Russian Arctic areas is important to assess the radioecological situation of these less-studied regions. Therefore, we investigated the sources of radionuclide contamination in Russian Arctic in the 1990s. Lichen and moss samples were collected from 1993 to 1996 in Kola Peninsula, Franz Josef Land, and few other locations. The activity concentration of ¹³⁷Cs was determined from the archived samples by gamma spectrometry in 2020. After radiochemical separation of Pu and U isotopes from the lichens and mosses, mass ratios ²⁴⁰Pu/²³⁹Pu, ²³⁴U/²³⁸U, ²³⁵U/²³⁸U, and ²³⁶U/²³⁸U were determined by mass spectrometry. ¹³⁷Cs activity concentrations at the sampling date were found to vary from 3.1 ± 1.4 (Inari, Finnish-Russian border) to 303 ± 7 (Kola Peninsula) Bq/kg. The ranges of isotopic ratios were 0.0592 ± 0.0007 to 0.253 ± 0.082 for ²⁴⁰Pu/²³⁹Pu, (4.89 ± 3.91) × 10^-5 to (6.86 ± 0.04) × 10^-5 for ²³⁴U/²³⁸U, 0.0072104(21) to 0.007376(41) for ²³⁵U/²³⁸U, and from below 1 × 10^-7 to (2.65 ± 0.19) × 10^-6 for ²³⁶U/²³⁸U, respectively. Based on the measured isotopic ratios and characteristic isotopic ratios of known contamination sources, the main Pu and U sources in the sampled lichens and mosses are global fallout, the Chernobyl accident, and possibly local nuclear activities. These results contribute to further understanding of past nuclear events and resulting nuclear contamination in Russian Arctic terrestrial areas.

Keywords: Arctic; Environmental radioactivity; Isotopic ratios; Nuclear contamination; Plutonium; Uranium.