Accumulation of technetium by cyanobacteria

Accumulation of pertechnetate ions (⁹⁹TcO₄^–) by the cyanobacterial speciesSynechocystis PCC 6803,Synechococcus PCC 6301,Plectonema boryanum,Anabaena variabilis and a redOscillatoria 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 inA. variabilis, P. boryanum and the redOscillatoria 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 inSynechococcus PCC 6301 and Ca²⁺ increased accumulation by the redOscillatoria. Some anions decreased TcO₄^– accumulation; CO₃^2– inA. variabilis and the redOscillatoria, SO₄^2– inSynechocystis PCC 6803, and HCO₃^– inP. 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.(*author for correspondence)