Radiotoxicity of plutonium in NTA-degrading Chelatobacter heintzii cell suspensions

The radiotoxicity of plutonium in NTA-degrading Chelatobacter heintzii cell suspensions was investigated as part of a more general study to establish the key interactions between actinide-organic complexes and microorganisms in the subsurface. The radiation tolerance of C. heintzii, based on Co-60 g amma irradiation experiments, was 165 +/- 30 Gy. No bacteria survived irrad iation doses greater than 500 Gy. In the presence of plutonium, where alpha particle decay was the primary source of ionizing radiation, the observed toxicity was predominantly radiolytic rather than chemical. This was eviden t by the greater effect of activity, rather than concentration, on the toxi city noted. Bioassociation of plutonium with C. heintzii was postulated to be an important and necessary step in the observed loss of cell viability s ince this was the best way to account for the observed death rate. The radi otoxicity of plutonium towards bacteria is a potentially important consider ation in the bioremediation of sites contaminated with radionuclide-organic mixtures and the bioprocessing of nuclear waste.