Potential effects of bacteria on radionuclide transport from a Swedish high level nuclear waste repository

Microorganisms can influence radionuclide migration if their concentration are high in comparison with other organic particles. Data on the numbers of microorganisms in undisturbed ground-water have been collected. The average number of cells in the samples from 17 levels in 5 boreholes was 3.0 x 105 cells ml-1. A biofilm experiment indicated an active microbial rock surface population. Radiographic uptake experiments suggest inactive bulk water populations. The bulk water microbial cells in deep ground water might then be inactive cells detached from active biofilms. Enrichment cultures for anaerobic bacteria demonstrated the presence of anaerobic bacteria capable of growth on C-1 compounds with hydrogen and carbon dioxide, presumably methanogenic bacteria. Further, growth in enrichment cultures with sulphate as electron-acceptor and lactate as carbon source proved dissimilatory sulphate reducing bacteria to be present. (author)