Can we predict uranium bioavailability based on soil parameters? Part 1: Effect of soil parameters on soil solution uranium concentration

Present study aims to quantify the influence of soil parameters on soil solution uranium concentration for 238U spiked soils. Eighteen soils collected under pasture were selected such that they covered a wide range for those parameters hypothesised as being potentially important in determining U sorption. Maximum soil solution uranium concentrations were observed at alkaline pH, high inorganic carbon content and low cation exchange capacity, organic matter content, clay content, amorphous Fe and phosphate levels. Except for the significant correlation between the solid-liquid distribution coefficients (Kd, L kg-1) and the organic matter content (R2=0.70) and amorphous Fe content (R2= 0.63), there was no single soil parameter significantly explaining the soil solution uranium concentration (which varied 100-fold). Above pH=6, log(Kd) was linearly related with pH [log(Kd) = -1.18 pH + 10.8, R²=0.65]. Multiple linear regression analysis did result in improved predictions of the soil solution uranium concentration but the model was complex.