DIRECT AND INDIRECT EFFECTS OF MICROBES ON TECHNETIUM INSOLUBILIZATION IN PADDY FIELDS
Direct and indirect effects of microorganisms on technetium insolubilization in water covering waterlogged soils were studied. Seven soils were waterlogged and then the water covering the soils were collected for further tracer experiments. The samples in contact with air were incubated with 95mTcO4--at 25 C for 4 to 5 days. After incubation, the samples were sequentially separated into four fractions: one insoluble fraction (> 0.2 {micro}m) and three soluble fractions (TcO4 -, cationic, and other forms). The radioactivity of 95mTc in each fraction was measured with a NaI (Tl) scintillation counter. The insolubility of Tc was observed in the untreated samples. The maximum insolubilization radioactivity was 37% of the total radioactivity in P38, which was collected from a paddy field, gray lowland soil. Microscopic observations revealed that bacteria were the dominant species in the insoluble fraction of P38. For the other samples, less than 9% of the Tc was found in insoluble form. In order to clarify biological and nonbiological factor affecting the insolubility, a reducing agent or nutrients were added to the P38 sample. The amount of insoluble Tc was enhanced by the addition of nutrients, while the addition of the reducing agent resulted in a dramatic decrease in the amount of the insoluble Tc. Most of the 95mTcO4 - added to the filtered or autoclaved samples was present in the form of the pertechnetate anion, even in P38. The filtered and autoclaved samples contained metabolites and dead cell particles, respectively. These materials, therefore, did not affect the physicochemical changes in Tc. These results suggest that specific bacteria having the ability to render Tc insoluble even under not strictly anaerobic conditions directly contribute to the insolubility of Tc.
- Research Organization:
- Office of Biospheric Assessment for Waste Disposal, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba-shi, 263-855 (JP)
- Sponsoring Organization:
- US Department of Energy (US)
- OSTI ID:
- 827058
- Resource Relation:
- Conference: Waste Management 2003 Symposium, Tucson, AZ (US), 02/23/2003--02/27/2003; Other Information: PBD: 27 Feb 2003
- Country of Publication:
- United States
- Language:
- English
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