Copper complexation by Cyanophyta and Chlorophyta exudates

Several freshwater phytoplanktonic species (eukaryotic and prokaryotic) wer e grown in batch cultures up to stationary phase and quantified by chloroph yll a analysis. The complexation properties (conditional stability constant and total ligand concentration) of their exudates were investigated by com plexometric titrations of the culture media using either copper or lead ion -selective electrodes. For most algae, Scatchard plot analysis of the titra tion data revealed two classes of copper-complexing ligands, one weaker and the other stronger. Strong copper-complexing agents were produced by Cyano phyta mainly in stationary growth phase. During exponential phase, ligand c oncentrations and the affinity for copper were similar for both Chlorophyta and Cyanophyta. Complexation parameters for Chlorophyta exudates were simi lar for both growth phases: exponential and stationary. In contrast, ligand concentrations were similar for Cyanophyta, but the conditional stability constants (the strength of association between ligand and metal) were diffe rent. Weak lead-complexing ligands were produced exclusively by two Chlorop hyta.