Accumulation of technetium by cyanobacteria

Accumulation of pertechnetate ions (⁹⁹TcO₄^-) by the cyanobacterial species Synechocystis PCC 6803, Synechococcus PCC 6301, Plectonema boryanum, Anabaena variabilis and a red Oscillatoria sp. consisted solely of a single rapid energy-independent phase (biosorption); no energy-dependent uptake was detected. Biosorption of TcO₄^- was concentration-dependent and could be described by a Freundlich adsorption isotherm for each cyanobacterial species examined. Decreasing pH increased the accumulation of TcO₄^- by all the species as did an increase in external NaCl concentration. Accumulation of TcO₄^- was also increased in A. variabilis, P. boryanum and the red Oscillatoria by an increased external osmotic potential. Concentrations of cations affected TcO₄^- accumulation; K⁺ increased accumulation in all the species, Mg²⁺, Ca²⁺, Sr²⁺ and Cs⁺ increased accumulation in Synechococcus PCC 6301 and Ca²⁺ increased accumulation by the red Oscillatoria. Some anions decreased TcO₄^- accumulation; CO₃^2- in A. variabilis and the red Oscillatoria, SO₄^2- in Synechocystis PCC 6803, and HCO₃^- in P. boryanum. The majority of TcO₄^- accumulated by all the cyanobacteria was easily desorbed, with no difference in the amounts desorbed between desorption agents of different pH or cation concentration.