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

The transformation of the floodplain hydrological regime due to climate change and human activity 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 to 100% of its full moisture capacity causes the redistribution of 137Cs and 90Sr speciation. Soil saturation with water increases the proportion of water-soluble 137Cs while the proportion of water-soluble 90Sr drops. 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. The proportion of 90Sr was observed to rise significantly in sod-gley soil developed on sandy alluvium as soil moisture increased but 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 this manner, but when water content reaches 100% of full moisture capacity in sod-gley soil, the proportion of the mobile form of this radioisotope drops dramatically. There is a general trend towards increased proportions of bioavailable forms of 137Cs and 90Sr in alluvial soils when their moisture content rises although the peculiarities and magnitude of this phenomenon depend on specific soil characteristics.