Uptake of technetium by freshwater green microalgae

Summary Accumulation of [⁹⁹Tc]pertechnetate ions (⁹⁹TcO₄^–) by the freshwater microalgae Chlorella emersonii, Chlamydomonas reinhardtii and Scenedesmus obliquus has been characterized. In all three species, accumulation consisted of a single rapid energy-independent phase (biosorption), and no energy-dependent accumulation was observed. Biosorption of ⁹⁹TcO_inf4^sup–by all three species was concentration dependent, followed a Freundlich adsorption isotherm, and was dependent on pH with increased accumulation by cells with decreasing external pH. Elevated external NaCl concentrations also caused increased accumulation of ⁹⁹TcO_inf4^sup–by the cells, as did increased external osmotic potential. Concentrations of K⁺, Mg²⁺ and Ca²⁺ increased accumulation of ⁹⁹TcO_inf4^sup–, but concentrations of HCO_inf3^sup–, SO_inf4^sup2–and CO_inf3^sup2–decreased ⁹⁹TcO_inf4^sup–accumulation by the cells. Most of the ⁹⁹TcO_inf4^sup–accumulated by all three species was easily desorbed by 10 mm buffers at various pH values, 0.5 m NaCl, 10 mm Na₂CO₃ or 10 mm Na₂SO₄. No differences in the amount of desorption were observed between the various desorption agents used.Correspondence to: G. M. Gadd