Uptake of technetium by freshwater green microalgae

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 m m buffers at various pH values, 0.5 m NaCl, 10 m m Na₂CO₃ or 10 m m Na₂SO₄. No differences in the amount of desorption were observed between the various desorption agents used.