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Keywords:

  • Key index words: adsorption;
  • copper;
  • ligands;
  • metal speciation;
  • Scenedesmus;
  • uptake

ABSTRACT

Copper (II) accumulation has been investigated in the green alga Scenedesmus subspicatus G. Brinkmann considering both adsorption and uptake kinetics. Experiments were conducted in a Cu- and PH-buffered medium at different free Cu2+ concentrations that were neither growth limiting nor toxic. We distinguished between adsorption on the cell surface and intracellular uptake by extracting copper from the cells with EDTA. Data from short-term experiments were compared with data obtained from experiments under steady state conditions. The accumulation of Cu can be described by two processes, an initial fast adsorption occurring within a minute followed by a slower intracellular uptake. Metal uptake followed Michaelis-Menten kinetics and is mediated by two systems, one with low and the other with high affinity. The maximum uptake rates (1.30 × 10-10 mol·[g dry wt algae]−1· min−1, 3.67 × 10-9 mol·[g dry wt algae]−1·min−1), and the half-saturation constants (6.84 × 10-14 M, 2.82 × 10-12 M) for the two uptake systems were determined using the Lineweaver-Burk plot. The calculated maximum concentration of binding sites on the surface of the algae is initially higher (9.0 × 10-6 mol Cu.[g dry wt algae]−1) than under steady state conditions (2.9 × 10-6 mol Cu·[g dry wt algae]−1). This suggests that the initial binding to the algal surface comprises the binding to specific transport ligands as well as to inert adsorption sites. The conditional stability constant of the Cu binding to surface ligands was calculated as log KCu= 11.0 at pH 7.9. This freshwater alga has a high ability to accumulate Cu, reflecting its adaptation to the bioavailable concentration of copper.