Accumulation of Cobalt, Zinc and Manganese by the Estuarine Green Microalga Chlorella Salina Immobilized in Alginate Microbeads

This paper describes cobalt, zinc, and manganese accumulation by Chlorella salina immobilized in calcium alginate microbeads, investigated by use of the radioisotopes ⁶⁰Co, ⁵⁴Mn, and ⁶⁵Zn. A rapid biosorption of the metals to C. salina cell walls and the alginate matrix, which was independent of light, temperature, or the metabolic inhibitor CCCP, was followed by a slower energy-dependent phase of uptake. Under similar conditions, immobilized cells accumulated greater amounts of Co, Zn, or Mn than free cells due to an increased active phase of uptake. Accumulation was also dependent on cell density in the alginate beads, with a greater uptake of cobalt at the highest cell densities. Desorption of cobalt from loaded beads was increased by decreasing pH and increasing concentrations of the cations, probably due to exchange of cobalt bound to the cell wall/alginate matrix for H⁺ or cations.