Complexation of lead with unicellular algae exudates

• Published in: Toxicological and environmental chemistry Vol. 69; no. 3-4; pp. 321 - 334
• Main Authors: Capelo, Sofia, Mota, Ana M., Gonçalves, Maria L.S.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.04.1999
• Subjects: Algae; lead; toxicity; voltammetry
• ISSN: 0277-2248; 1029-0486
• DOI: 10.1080/02772249909358714

Release of exudates by freshwater algae may be different in polluted and non-polluted waters. The purpose of this work is to study the effect of lead on the unicellular green algae (Selenstrum capricornutum Printz), to find out if algae develop some defence mechanism against lead toxicity. Complexation studies were done in lead contaminated and uncontaminated (control) cultures, in exponential and stationary growing phases. The titrations of the different samples with Pb 2+ were followed by differential pulse anodic stripping voltammetry, associated with three different types of working electrodes: hanging mercury drop, thin mercury film and nafion-coated thin mercury film. Their behaviour was compared, and it was found that nafion-modified electrode is the best choice to avoid interferences due to adsorption of the exudates at the electrochemical interface. The algae release two different types of ligands in terms of complexing affinity and dissociation rate constant, in both control and contaminated media. One type forms labile complexes with lead, within the time scale of the voltammetric technique, with a complexing stability constant of about 3 in log units. The other type, with a much lower concentration, forms stronger complexes with log K ML = 15 and an inert behaviour. In Pb contaminated cultures the alga releases a higher concentration of inert sites, probably contributing to their own detoxification.