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(P182) Effects of natural dissolved organic matter on silver speciation and silver uptake by a green alga.
Porcher, Céline*,1, Campbell, Peter1, 1 Institut national de la Recherche scientifique - ETE, Québec city, QC, Canada
ABSTRACT- The geochemical cycle of silver has been perturbed by anthropogenic activities, but we know relatively little about its ecotoxicological effects. The amplitude of any such effects will be strongly influenced by silver speciation. Natural ligands likely to influence the speciation of silver in the environment include chloride, thiosulfate, sulfide and natural DOM; the present project focuses on natural DOM (humic and fulvic acids). The experimental design involves exposing a green alga, Chlamydomonas reinhardtii, to a fixed free Ag+ concentration, in the presence or absence of NOM. To measure free Ag+ we have adapted an equilibrium ion exchange technique (Int. J. Environ. Anal. Chem. 72: 173-194 ). The technique was first validated for Ag+ in the presence of Cl-, since the complexation constants for the reactions of Ag with chloride are well established. The sulfonate resin appears to be selective for the free metal ion when solutions containing Ag+ and the various chloro-complexes are passed through the ion exchange column. The calibrated resin was then used to measure free silver in the presence of Suwannee River humic and fulvic acids; results for solutions containing 5-100 nM Ag and realistic organic carbon concentrations (5 mg C/L) indicate that the natural DOM has a very high affinity for silver. The results of these titration experiments allowed us to define appropriate exposure conditions for the algal uptake experiments. These experiments will allow us to determine if silver uptake in the presence of natural DOM follows the predictions of the Biotic Ligand Model.
Key words: silver, algae, uptake, humic acid
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