title: Copper and cadmium complexation by Cylindrospermopsis raciborskii exudates.
abstract: 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.
authors.affiliation: Department 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: aletonietto@gmail.com.
authors.forename: Alessandra Emanuele
authors.initials: AE
authors.lastname: Tonietto
authors.affiliation: Department of Statistics, Federal University of São Carlos, Via Washington Luis km 235, São Carlos, São Paulo CEP 13565-905, Brazil.
authors.forename: Natalia L
authors.initials: NL
authors.lastname: Oliveira
authors.affiliation: Department 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: aletonietto@gmail.com.
authors.forename: Ana Teresa
authors.initials: AT
authors.lastname: Lombardi
authors.affiliation: Department of Statistics, Federal University of São Carlos, Via Washington Luis km 235, São Carlos, São Paulo CEP 13565-905, Brazil.
authors.forename: Adriano
authors.initials: A
authors.lastname: Polpo
mesh_terms: D001499:Bayes Theorem; D002104:Cadmium / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D046891:Cylindrospermopsis / Q000378:metabolism*; D008024:Ligands; D008970:Molecular Weight; D009930:Organic Chemicals / Q000737:chemistry*
chemical_list: D008024:Ligands; D009930:Organic Chemicals; D002104:Cadmium; D003300:Copper