Influence of Moisture Regime on the Redistribution of Radioactive Cesium and Strontium Isotopes in Alluvial Soils by Physico-Chemical Forms

The transformation of the hydrological regime of floodplains due to climate change and anthropogenic impact on water redistribution processes within natural landscapes can significantly impact the bioavailability of long-lived radioactive isotopes of cesium and strontium. A laboratory experiment demonstrated that varying the moisture content of alluvial soil within 40–100% from its full water-holding capacity leads to the redistribution of ¹³⁷Cs and ⁹⁰Sr between different chemical forms. Soil saturation with water increases the proportion of water-soluble ¹³⁷Cs, while the proportion of water-soluble ⁹⁰Sr decreases. The ion-exchangeable form of ¹³⁷Cs remains unaffected by soil moisture. The behavior of the ion-exchangeable form of ⁹⁰Sr in response to changes in soil moisture is dependent on soil characteristics: a significant increase in the proportion of ⁹⁰Sr was observed in sod-gley soil developed on sandy alluvium as soil moisture increased; however, this phenomenon was not observed in sod-gleyed soil developed on loamy alluvium. The proportion of ¹³⁷Cs extracted by sodium tetraphenylborate increases when alluvial soils are saturated with water. Similarly, the mobile form of ⁹⁰Sr behaves in the same manner, but when soil moisture reaches 100% of its full water-holding capacity in sod-gley soil, a sharp decrease in the proportion of the mobile form of this radionuclide is observed. Overall, there is a trend towards increased proportions of bioavailable forms of ¹³⁷Cs and ⁹⁰Sr in alluvial soils with increased moisture content, although the pecularities and magnitude of this phenomenon depend on the specific soil characteristics.