Plant uptake of radionuclides in lysimeter experiments

The results of seven years lysimeter experiments to determine the uptake of Co-60, Cs-137 and Ra-226 into agricultural crops (endive, maize, wheat, mustard, sugarbeet, potato, Faba bean, rye grass) are described. The lysimeter consists of twelve monolithic soil profiles (four soil types and three replicates) and is located in Seibersdorf/Austria, a region with a pannonian climate (pronounced differences between hot and semi-arid summers and humid winter conditions, annual mean of precipitation: 517 mm, mean annual temperature: 9.8 degrees C). Besides soil-to-plant transfer factors (TF), fluxes were calculated taking into account biomass production and growth time. Total median values of TF's (dry matter basis) for the three radionuclides decreased from Ra-226 (0.068 kg kg(-1)) to Cs-137 (0.043 kg kg(-l)) and Co-60 (0.018 kg kg(-1)); flux values exhibited the same ranking. The varying physical and chemical properties of the four experimental soils resulted in statistically significant differences in transfer factors or fluxes between the investigated soils for Cs-137 and R-226, but not for Co-60. Differences in transfer between plant species and plant parts are distinct, with graminaceous species showing, on average, TF values 5.8 and 15 times lower than dicotyledonous species for Cs-137 and( 60)Co, respectively. This pattern was not found for Ra-226. It can be concluded that Cs-137 transfer is heavily influenced by soil characteristics, whilst the plant-specific factors are the main source of TF variability for Co-60. The variability of Ra-226 transfer originates both from soil properties and plant species behaviour. (C) 1998 Elsevier Science Ltd. All rights reserved.