Bradac Philippe, Behra Renata, Sigg Laura
Eawag, Swiss Federal Institute of Aquatic Science and Technology, P.O. Box 611, CH-8600 Duebendorf, Switzerland.
Environ Sci Technol. 2009 Oct 1;43(19):7291-6. doi: 10.1021/es9013536.
The relationship between cadmium speciation and accumulation in periphyton was examined at environmentally relevant Cd concentrations under natural freshwater conditions. Periphyton was exposed in artificial recirculating channels containing natural freshwater to two Cd concentrations (20 and 40 nM), for which speciation was modified by the addition of a synthetic organic ligand (nitrilotriacetate, NTA). Labile metal concentrations were measured with the technique of diffusion gradient in thin-films (DGT) and major Cd species were estimated by modeling. Total and intracellular Cd content in periphyton increased within both Cd exposure concentrations with NTA additions and were related to an increase in DGT-labile Cd, which was caused by the competition of NTA with probably colloidal species. Bioaccumulation was thus not controlled by the free Cd concentrations, as predicted by the free ion activity model, but by the diffusion of labile Cd-NTA complexes, which constituted a large fraction of DGT-labile Cd. These findings confirm the importance of labile species for Cd accumulation in periphyton under freshwater conditions, as predicted by models considering diffusion and uptake kinetics.
在天然淡水条件下，于与环境相关的镉浓度水平下，研究了周丛生物中镉的形态与积累之间的关系。将周丛生物置于含有天然淡水的人工循环渠道中，暴露于两种镉浓度（20和40 nM）下，通过添加一种合成有机配体（次氮基三乙酸，NTA）来改变其形态。采用薄膜扩散梯度技术（DGT）测量不稳定金属浓度，并通过建模估算主要镉形态。添加NTA后，在两种镉暴露浓度下，周丛生物中的总镉含量和细胞内镉含量均增加，且与DGT-不稳定镉的增加有关，这是由NTA与可能的胶体物质竞争所致。因此，生物积累并非如自由离子活性模型所预测的那样受游离镉浓度控制，而是受构成DGT-不稳定镉很大一部分的不稳定镉- NTA络合物的扩散控制。这些发现证实了不稳定形态对于淡水条件下周丛生物中镉积累的重要性，正如考虑扩散和吸收动力学的模型所预测的那样。
