Fractionation of natural radionuclides in soils from the vicinity of a former uranium mine Žirovski vrh, Slovenia

As a result of former uranium mining and milling activities at Žirovski vrh, Slovenia, 0.6 million tons of uranium mill tailings (UMT) were deposited onto a nearby waste pile Boršt. Resulting enhanced levels of natural radionuclides in UMT could pose threat for the surrounding environment. Therefore, sequential extraction protocol was performed to assess mobility and bioavailability of 238U, 234U, 230Th and 226Ra in soils from the waste pile and its surrounding. The radionuclides associated with exchangeable, organic, carbonate, Fe/Mn oxides and residual fraction, respectively, were determined. Results showed that the highest activity concentrations for the studied radionuclides were on the bottom of the waste pile. In non-contaminated locations, about 80% of all radionuclides were in the residual fraction. Considering activity concentrations in the UMT, 238U and 234U are the most mobile. Mobility of 226Ra is suppressed by high sulphate concentrations and is similar to mobility of 230Th.