Аннотация:The 226Ra, 238U, and 232Th fractions have been studied in the virgin gray soil under the forest and in the agro-gray soil of the Tula forest entanglements (Tula Zaseki). Radionuclides have been fractionated by Pavlotskaya’s sequential extraction method. The 238U and 232Th concentrations have been determined with an inductively coupled plasma quadrupole mass spectrometer. The 226Ra activity has been measured using an alpha-radiometer, taking into account the decay of radium isotopes and the accumulation of their daughter decay-related products. Long-term (decades) and systematic use of phosphorus fertilizers leads to an increase in 226Ra, 238U, and 232Th reserves in the ploughed layer (0–25 cm) of the agro-gray soil to levels of 15.1, 15.4, and 16.2 kBq/m2, respectively, which is 1.7, 1.4, and 1.1 times higher than in the virgin gray soil under the forest. Alongside with that, a considerable amount of radionuclides (21.9 % 226Ra, 9.8 % 238U, and 4.8 % 232Th entering the soil along with phosphate fertilizers) remains available to plants due to their accumulation in the exchangeable fraction. Among the potentially mobile fractions for 238U and 232Th forms, along with the exchangeable fraction, the mobile fraction “proper” (extracted by 1M HCl) is also important.
