Meylan Sébastien, Behra Renata, Sigg Laura
Swiss Federal Institute of Environmental Science and Technology (EAWAG), PO Box 611, CH-8600 Dübendorf, Switzerland.
Environ Sci Technol. 2004 Jun 1;38(11):3104-11. doi: 10.1021/es034993n.
The free ion activity model (FIAM) has already been confirmed under laboratory conditions for many trace metals but has still to be validated under natural conditions where the presence of natural organic ligands influences metal speciation and bioavailability. The goal of this study was to test if the FIAM is followed under natural conditions by measuring copper and zinc speciation as well as metal accumulation in periphyton. Periphyton was exposed in microcosms to natural river water with different added concentrations of copper (25-258 nM) or zinc (18-501 nM) and additions of a synthetic ligand (NTA). Free Cu2+ was in the range of 10(-16.5)-10(-14.5) M and Zn(2+) was in the range of 0.7-8.7 nM, as measured by competitive ligand exchange coupled with cathodic/anodic stripping voltammetry. Other metal complexes were either measured or computed. Bioaccumulation of zinc in periphyton appeared to be controlled by the free zinc ion concentration, confirming the FIAM. In contrast, bioaccumulation of copper was controlled by weakly complexed copper (including Cu2+ plus inorganic and weak organic complexes), which is in disagreement with the FIAM, and appears to be caused by limitation of copper diffusion due to very low free Cu2+ occurring in natural environments.
自由离子活性模型（FIAM）已在实验室条件下针对多种痕量金属得到证实，但在自然条件下仍有待验证，因为天然有机配体的存在会影响金属的形态和生物可利用性。本研究的目的是通过测量铜和锌的形态以及周丛生物中的金属积累，来测试在自然条件下是否遵循FIAM。将周丛生物置于微观世界中，暴露于添加了不同浓度铜（25 - 258 nM）或锌（18 - 501 nM）以及添加了合成配体（NTA）的天然河水中。通过竞争配体交换结合阴极/阳极溶出伏安法测定，游离Cu2+的浓度范围为10(-16.5)-10(-14.5) M，Zn(2+)的浓度范围为0.7 - 8.7 nM。对其他金属络合物进行了测量或计算。周丛生物中锌的生物积累似乎受游离锌离子浓度控制，这证实了FIAM。相比之下，铜的生物积累受弱络合铜（包括Cu2+加上无机和弱有机络合物）控制，这与FIAM不一致，似乎是由于自然环境中游离Cu2+浓度极低导致铜扩散受限所致。
