Mobility and bioavailability parameter values for impact assessment for NORM sites: can they be predicted?

The solid-liquid distribution coefficient and the soil-to-plant transfer factor are two important parameters in the assessment of the dose to man through contamination of the food chain. The solid-liquid distribution coefficient (Kd) determines the mobility of an element and the soil-to-plant transfer factor (TF) indicates to facility of uptake by crops. Both parameters depend on soil characteristics. There is a large variability in Kd and TF values with implications for impact assessment. Reducing the variability and uncertainty in these parameter values within a given assessment context will result in more realistic and robust impact assessments. More information on factors influencing sorption and bioavailability such as pH, CEC, clay content and organic matter content should be collated. Research is needed to increase the understanding in the mechanisms governing radionuclide-soil-plant interaction. Until we have acquired this increased understanding and improved database for developing parameterized models, the proposed best estimates are suitable for screening assessments, but site specific impact assessment will remain to rely on site specific investigations of Kd and TF instead of on site specific predictions of Kd and TF.