Curium-244 uptake in freshwater snails

Laboratory experiments were conducted to determine the bioavailability of 244Cm to the pond snail Lymnaea stagnalis L. The uptake was determined in water with and without organic matter. The organic material was isolated from natural bog lake water by ultrafiltration and it was added to synthetically prepared water at a concentration of 10 mg/l. 244Cm was present for 50 - 80% in particulate form (> 0.45 μm) in the solutions without organic matter. When natural organic acids were present (10 mg/l), less than 25% of the curium was in particulate form. Accumulation of the radionuclide by the snails, measured over a period of 21 days, yielded concentration factors (CF = radioactivity of 244Cm kg-1 animal wet weight/radioactivity 1-1 water) ranging from 200 to 300. Around 84% of the radionuclide in the snail was measured in the soft tissues. Only 16% of the 244Cm was fixed to the shell. High CF values were measured in the hepatopancreas, ranging from 4000 to 7000. The relative distribution of the radionulide among the snail's tissues did not vary with the water type. Concentration factors were 1.6 times higher for snails in water without added organic, thus suggesting that uptake was highest from solutions with high contents of particulate 244Cm. The presented results for snails clearly indicated that 244Cm more than 241Am became assimilated in soft tissues leading to high concentration factors in tissues and organs. This observation may have considerable radioecological consequences especially because dose assessment models for risk evalaution often extrapolate the data of 241Am to evaluate the risk of 244Cm