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Environmental context Metal–carbonato complexes have been reported to contribute to metal uptake and toxicity in aquatic organisms. We show that in the presence of lead–carbonato complexes, Pb internalisation by the microalga Chlamydomonas reinhardtii is higher than that predicted on the basis of the free Pb 2+ concentration. This effect, which was not observed for another microalga that takes up Pb more slowly, is attributed to the very high rates of Pb uptake by C. reinhardtii , which result in diffusion limitation. Abstract The possible contribution of metal–carbonato complexes to metal uptake or toxicity has been mentioned several times in the literature, often in studies where dissolved inorganic carbon (DIC) concentrations and pH were varied together, but a thorough study of the effect on DIC on metal bioavailability to aquatic organisms has not been done. By using closed systems – allowing changes in DIC concentrations at fixed pH – and ion selective electrodes to determine free metal ion concentrations, we show that lead internalisation by the unicellular alga Chlamydomonas reinhardtii in the presence of high DIC concentrations is higher than predicted by the free Pb 2+ ion concentration at bulk (Pb 2+ ) lower than 50 nM, but not at higher (Pb 2+ ). This effect is not observed for another microalga, Chlorella vulgaris , which shows a lower rate of Pb internalisation. Copper internalisation by C. reinhardtii seems also to be slightly higher than predicted on the basis of free Cu 2+ at low (20 nM) bulk Cu 2+ concentrations but not at higher ones. The possibility that Pb (and Cu) internalisation by C. reinhardtii is partially limited by diffusion from the bulk solution to the algal surface is identified and discussed as a possible explanation for these results.
Environmental Chemistry – CSIRO Publishing
Published: May 9, 2013
Keywords: biotic ligand model, dissolved inorganic carbon, metal bioavailability, metal uptake.
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