Influence of salinity and eutrophication on bioaccumulation of (99)Technetium in duckweed

This study concerns the bioaccumulation of the long-Lived nuclear waste pro duct Tc-99 in duckweed (Lemna minor L.). Tc-99 was present as the. oxyanion TcO4-, being the main chemical form of technetium in aerobic water systems . In contrast with terrestrial plants, bioaccumulation in duckweed proved t o be independent of the nitrate concentration in the medium. However, uptak e is controlled by electrostatic effects in the cell wall, which affects th e bioaccumulation of Tc-99 in duckweed in natural environments. These water s are characterized by a range of salinity and hardness, and this study sug gests that this may result in up to a threefold difference in Tc-99 accumul ation. Because of screening of negative charges in the cell wall, the highe st accumulation may be expected in hard, brackish water. This behavior can be described by a general model, which includes electrostatic effects and b inding of cations at the cell wall. The model also explains why cationic ra dionuclides are preferably taken up in soft, fresh water while anionic spec ies are concomitantly taken up in hard, chlorine-rich waters.