Evolution of Sr distribution coefficient as a function of time, incubation conditions and measurement technique

A thorough understanding of the dynamics of radiostrontium in soil is required to allow accurate long-term predictions of its mobility. We have followed the soil solution distribution of 85Sr as a function of time under controlled conditions over 4 months and studied the effect of soil moisture content and organic matter amendments. Data have been compared to redox conditions and soil pH. To fuel the ongoing debate on the validity of distribution coefficient (Kd) values measured in dilute suspension, we have compared values obtained from the activity concentration in soil solution obtained by centrifugation to data obtained in suspension with or without air-drying of the soil samples after incubation. The 85Sr adsorption properties of soil, incubated without prior contamination were also measured. There is some time-dependent adsorption of Sr. This is partly due to changing soil composition due to the decomposition of added organic matter and anaerobic conditions induced by flooding. There is also a kinetic effect, but adsorption remains largely reversible. Most of the observed effects are lost when soil is suspended in electrolyte solution.