John Wiley & Sons, Ltd.

Linking the chemical speciation of Ce to its bioavailability in water for a freshwater alga

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Over the past decade, researchers have begun to use metals of the lanthanide family for numerous applications, including liquid crystal display (LCD) screens, optical fibers and laser technology. Unfortunately, little is presently known about their bioavailability or the mechanisms by which they might cause toxicity. This paper focuses on cerium, which is one of the most widely used lanthanides, and focuses on validating the biotic ligand model as a means to predict Ce bioaccumulation. Short term exposures to Ce were performed using the unicellular alga, Chlamydomonas reinhardtii, in order to better relate Ce bioavailability to its chemical speciation in solution. Maximum uptake fluxes (Jmax) and affinity constants for the binding of cerium to the biological uptake sites (KS) were established at pH 5.0 and pH 7.0. An apparent affinity constant of 1.8 × 107 M−1 was observed at pH 5.0, with a larger value obtained at pH 7.0 (6 × 107 M−1), albeit under conditions where equilibrium could not be confirmed. By evaluating cerium speciation using centrifugal ultrafiltration and single particle inductively coupled plasma spectrometry, it could be concluded that very little (∼30%) cerium was truly dissolved at pH 7.0, with the majority of the metal being present in colloidal species. Speciation was also monitored by fluorescence in order to evaluate Ce complexation by natural organic matter (NOM). The presence of NOM increased decreased Ce bioaccumulation in line with free Ce concentrations. Finally, competition with calcium for the metal uptake sites was shown to result in a decrease in cerium uptake by C. reinhardtii. This article is protected by copyright. All rights reserved

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