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The role of complexation and competition in the biouptake of europium by a unicellular alga
Author(s) -
Yang Guang,
Tan QiaoGuo,
Zhu Lin,
Wilkinson Kevin J.
Publication year - 2014
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.2722
Subject(s) - europium , chemistry , ligand (biochemistry) , malic acid , citric acid , biotic ligand model , lanthanide , context (archaeology) , rare earth element , metal , rare earth , ion , mineralogy , biology , organic chemistry , biochemistry , receptor , paleontology
Short‐term (60 min) europium (Eu) biouptake fluxes by the freshwater green alga Chlamydomonas reinhardtii were investigated in the presence and absence of ligands (e.g., malic acid and citric acid) and a second rare earth metal, samarium (Sm). Data were interpreted in the context of the biotic ligand model, which uses experimentally determined stability constants to take into account the competition and complexation of the metal of interest. In the absence of ligands or competitors, Eu biouptake was well described by a Michaelis‐Menten equation with the maximal uptake flux ( J max ) and Michaelis‐Menten constant ( K m ) of J max = 1.7 × 10 −14 mol cm −2 s −1 and K m = 10 −7.0 M (corresponding to an affinity constant of 10 7.0 M −1 ). Biouptake of Eu (or Sm) decreased as the concentration of a competing rare earth element (i.e., Sm or Eu) increased, as predicted by the biotic ligand model. On the other hand, when hydrophilic complexes were formed with citric and malic acid, Eu biouptake was much greater than predicted on the basis of free ion concentrations alone. Overall, the results showed that for C. reinhardtii the rare earth elements were likely to share a common biouptake pathway; biouptake of one rare earth element was reduced when another was present, and rare earth element complexes were bioavailable. Environ Toxicol Chem 2014;33:2609–2615 . © 2014 SETAC