238U 226Ra 210Pb, 232Th and 40K activities in soil profiles of the Flysch sector (Central Spanish Pyrenees)

Distributions of natural gamma-emitting radionuclides were determined in three soil profiles developed on Tertiary sedimentary materials in mountain landscapes of the Central Spanish Pyrenees. Radioisotope activities (Bq kg(-1)) lie in the range of 0-53 for 238U; 19-33 for 226Ra; 7-75 for 210Pb; 24-48 for 232Th and 335-562 for 40K. 238U and 210Pb activities show an important variability down the soil profiles. 238U was markedly depleted in all upper soil layers and highly enriched in lower layers of two soil profiles. 210Pb exhibits very dissimilar distribution patterns in all three soils. 226Ra and 232Th had quite uniform depth distributions. 40K showed depletion in both upper and lower layers in one soil profile but remained fairly constant in the other two profiles. 238U/226Ra activity ratios (ARs) have been used to assess equilibrium in the 238U decay chain and as indicators of edaphogenesis in the studied soil profiles. Maintenance of initial proportionality in the ratio of 232Th/238U activities has been assessed through ARs of their progenies. Additionally, a variety of soil properties were measured down the soil profiles. Among soils, variation in radionuclide activies may be due to differences in carbonate content, organic matter and/or grain size. In this environment, soil properties differently affect mobilization of natural radionuclides. The association of some radiologic properties with soil layers suggest a relationship between soil processes and radionuclide distribution.