Microbial interactions with phosphorus containing glasses representative of vitrified radioactive waste

The presence of phosphorus in borosilicate glass (at 0.1 – 1.3 mol % P2O5) and in iron-phosphate glass (at 53 mol % P2O5) stimulated the growth and metabolic activity of anaerobic bacteria in model systems. Dissolution of these phosphorus containing glasses was either inhibited or accelerated by microbial metabolic activity, depending on the solution chemistry and the glass composition. The breakdown of organic carbon to volatile fatty acids increased glass dissolution. The interaction of microbially reduced Fe(II) with phosphorus-containing glass under anoxic conditions decreased dissolution rates, whereas the interaction of Fe(III) with phosphorus-containing glass under oxic conditions increased glass dissolution. Phosphorus addition to borosilicate glasses did not significantly affect the microbial species present, however, the diversity of the microbial community was enhanced on the surface of the iron phosphate glass. Results demonstrate the potential for microbes to influence the geochemistry of radioactive waste disposal environments with implication for wasteform durability. Vitrified radioactive waste is designed to immobilize long lived radionuclides for time periods up to 106 years until activity has decayed to safe levels. Radioactive elements are chemically incorporated in the glass network and so are released as the glass dissolves. It is, therefore, important to understand the durability of vitrified radioactive waste in subsurface environments to inform the safety case for their long-term disposal. This paper investigates glass-microbe interactions using non-active surrogates for radioactive waste glasses and relevant anaerobic microorganisms to build a mechanistic understanding of glass dissolution in complex natural environments.