137Cs and 90Sr root uptake prediction under close-to-real controlled conditions

Radionuclide soil-to-crop transfer was analysed in large undisturbed soil monoliths installed in lysimeters under controlled climatic conditions. The soils were representative of large agricultural areas in the European Union: Loamy-sand Orthic Podzol from Belgium, Loamysand Fluvisol from France, Loamy Calcic Luvisol from Spain, Silty-loam Orthic Luvisol from Germany, and Sandy-loam Eutric Fluvisol from the UK. On the lysimeters, winter barley was sown for two consecutive years on artificially contaminated soils simulating a post-accidental situation, 1 and 2 years after radionuclide deposition. The amount (Bq m-2) of 137Cs and 90Sr that accumulated in the crop was higher in the loamy-sand soils, regardless of the total radionuclides (MBq m-2) or available fraction content in the soil. The Orthic Podzol produced the highest 137Cs crop accumulation, and the Loamy-sand Fluvisol the highest 90Sr accumulation. Concentration ratios (CR) showed similar results, but with higher 90Sr transfer for the Podzol than for the Loamy-sand Fluvisol. The activity concentration of radionuclides in the plants was negatively correlated with crop yield, indicating that high crop productivity produced a general dilution effect in radionuclide concentration activity in plants. The relative radionuclide crop accumulation expressed in Bq m-2 was predicted from the soil availability parameters, that is the available 137Cs fraction divided by the distribution coefficient (KD) and by the K concentration in soil solution, and the available 90Sr divided by the cationic exchange capacity (CEC). These predictions could not be obtained when using the CR, as this does not fully account for the crop growing conditions which influence radionuclide uptake by the crop.