Cylindrospermopsis raciborskii is a potentially toxic cyanobacterium that excretes organic materials which act as ligands for metals. Metal ligands may be characterized for their strength of association, e.g., stability constants, which can be either thermodynamic (K) or conditional (K’). In this research we examined K and K’ for Cu and Cd complexes with three molecular weight fractions (>30 kDa; 30–10 kDa; 10–3 kDa) of the cyanobacteria EOM. Complexation capacities of the excreted organic materials (EOM) for metals were determined at several ionic strengths (1.0 × 10−2, 5.0 × 10−2, 1.0 × 10−1, and 5.0 × 10−1 mol L−1) at pH 6.6 ± 0.1, with ligands for which no data for their acidity constants are available; these constants are thus conditional for this specific pH. Bayesian statistics showed that with a probability of 95–100% the EOM have two different ligands for Cu but only one for Cd, that ligands for Cu were stronger than for Cd (94–100% probability), and that the smallest EOM fraction had the highest strength of association for Cu (logKCuL 13.5). The lowest affinity was obtained for Cd (logKCdL 8.6) complexed to any molecular weight fraction. The present findings have important ecological implications, since the metal–ligand association is dynamic, and together with a diversity of ligands it can act as an environmental metal buffer. As a result, higher metal loads may be necessary for the detection of toxicity.
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Research Article|
March 04 2016
Copper and cadmium complexation by Cylindrospermopsis raciborskii exudates
Alessandra Emanuele Tonietto;
1Department of Botany, Federal University of São Carlos, Via Washington Luis km 235, PO Box 676, São Carlos, São Paulo CEP 13565-905, Brazil
E-mail: [email protected]
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Natalia L. Oliveira;
Natalia L. Oliveira
2Department of Statistics, Federal University of São Carlos, Via Washington Luis km 235, São Carlos, São Paulo CEP 13565-905, Brazil
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Ana Teresa Lombardi;
Ana Teresa Lombardi
1Department of Botany, Federal University of São Carlos, Via Washington Luis km 235, PO Box 676, São Carlos, São Paulo CEP 13565-905, Brazil
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Adriano Polpo
Adriano Polpo
2Department of Statistics, Federal University of São Carlos, Via Washington Luis km 235, São Carlos, São Paulo CEP 13565-905, Brazil
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Water Sci Technol (2016) 73 (10): 2544–2551.
Article history
Received:
July 20 2015
Accepted:
February 15 2016
Citation
Alessandra Emanuele Tonietto, Natalia L. Oliveira, Ana Teresa Lombardi, Adriano Polpo; Copper and cadmium complexation by Cylindrospermopsis raciborskii exudates. Water Sci Technol 18 May 2016; 73 (10): 2544–2551. doi: https://doi.org/10.2166/wst.2016.111
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