Influence of physicochemical properties of the soil solution on the 226Ra distribution coefficient in soils

Abstract

Defined as the ratio between the isotope’s activity concentrations in the solid fraction of the soil and in the soil solution, the distribution coefficient (Kd) of 226Ra is an equilibrium constant that encompasses all the interface processes that comprise its sorption as a whole. However, there is a great variability in the reported measured values of radium Kd. A first classification of soils in terms of their texture reduces this variability somewhat, but the chemical environment of the soil solution is also expected to exert a significant influence on the sorption process and therefore on the Kd. In the present work, linear regressions are applied to look for relationships between the radium Kd and the physicochemical properties of the soil solution. The soil solutions were studied of three soils with different textural characteristics but taken from the same natural soil. For the soil classified as loamy coarse sand, the significant independent variables affecting Kd were the pH, conductivity, and dissolved organic matter; for the soil classified as loamy fine sand, they were the bivalent cation concentration and pH; and for the soil classified as loam, they were the conductivity and nitrate concentration.