Epifluorescence microscopy was utilized to enumerate halophilic bacterial
populations in two studies involving inoculated, actual radioactive
waste/brine mixtures and pure brine solutions. The studies include an
initial set of experiments designed to elucidate potential transformations
of actinide-containing wastes under salt-repository conditions, including
microbially mediated changes.
The first study included periodic enumeration of bacterial populations of a
mixed inoculum initially added to a collection of test containers. The
contents of the test containers are the different types of actual
radioactive waste that could potentially be stored in nuclear waste
repositories in a salt environment. The transuranic waste was generated from
materials used in actinide laboratory research. The results show that cell
numbers decreased with time. Sorption of the bacteria to solid surfaces in
the test system is discussed as a possible mechanism for the decrease in
The second study was designed to determine radiological and/or chemical
effects of 239Pu, 243Am, 237Np,
232Th and 238U on the growth of pure and mixed
anaerobic, denitrifying bacterial cultures in brine media. Pu, Am, and Np
isotopes at concentrations of ≤1×10–5M, ≤5×10–6M and ≤5×10-4 M
respectively, and Th and U isotopes at concentrations of ≤4×10-3
M were tested in these media. The results indicate that high actinide
concentrations affected both the bacterial growth rate and morphology.
However, relatively minor effects from Am were observed at all tested
concentrations with the pure culture.