Elevated natural radioactivity in undisturbed forest and mountain areas of arctic Norway – local geology, soil characteristics, and transfer to biota. (October 2020)

• Record Type: Journal Article
• Authors: Thørring, Håvard; Wærsted, Frøydis Meen; Raaness, Agnes; Skipperud, Lindis; Jensen, Louise Kiel
• Is Part Of: Journal of environmental radioactivity. Volume 222(2020)
• Publication Date: 2020-10
• Subjects: Naturally occurring radionuclides -- Geological characterization -- Biological uptake -- Transfer factors -- Arctic ecosystem; Radioactivity -- Periodicals; Radiation, Background -- Periodicals; Radioecology -- Periodicals; Radioactive pollution -- Periodicals; Environmental Pollutants -- Periodicals; Radioactive Pollutants -- Periodicals; Radioactivity -- Periodicals; Radioécologie -- Périodiques; Pollution radioactive -- Périodiques; Fond de rayonnement -- Périodiques; 539.752
• DOI: 10.1016/j.jenvrad.2020.106291
• Languages: English
• ISSNs: 0265-931X

Abstract

Abstract: This study deals with the geology in areas close to a large unexploited uranium deposit and the impact of bedrock characteristics on levels of radionuclides and other elements in soil and biota. Factors influencing soil inventory and ecosystem transfer are discussed, focussing on 238 U, 226 Ra, and 210 Pb. Field work was carried out in Salangen Valley in Northern Norway. Sampling stations for soil and biota covered different habitats – grassland, birch forest and low alpine heathland. The geological survey confirmed uranium-bearing minerals in granitic gneiss and pegmatites. There was large variation in the local occurrence of uranium, reflecting the irregular nature of the pegmatite. Activity concentrations of 238 U, 226 Ra, and 210 Pb in surface soil were elevated at sites close to U-enhanced bedrock, compared to sites with other types of bedrock. Particularly high soil levels were found for 226 Ra and 210 Pb, whereas activity concentrations of 238 U were more variable, depending of local soil characteristics. Levels of other natural radionuclides ( 40 K, 232 Th) merely increased with soil mineral content, and concentrations of heavy metals were generally low at all sites. External dose rate (1 m above ground surface) was closely correlated with 226 Ra levels in soil. Plant levels of 238 U and 226 Ra varied by several orders of magnitude depending on soil level and plant species, whereas plant levels of 210 Pb and 210 Po were largely affected by aerial fallout. Berries generally contained lower levels of 238 U and 226 Ra than green plant parts. As was the case for plants, the levels of 238 U in earthworms were strongly correlated with the respective concentrations in the soil. Soil-to-plant transfer was markedly higher for 226 Ra than for 238 U. For both radionuclides, a positive correlation was found between concentration ratios of V. myrtillus (heath) and soil organic matter content. The 238 U concentration ratios for earthworms were generally two orders of magnitude higher than for plants. Graphical abstract: Image 1 Highlights: Distribution of naturally occurring radionuclides in undisturbed areas. Geological characterization supports variation in soil inventory of radionuclides. Transfer data to biota covering a gradient of soil activity concentrations. Plant activity concentrations and transfer was highest for radium-226.