In order to clarify the technetium behavior in paddy field ecosystem, insolubilization of technetium in the water covering waterlogged soils was studied. Fourteen soils collected from paddy fields (9 samples) and upland fields (5 samples) were waterlogged for 7 days. After the collection of water covering the waterlogged soils, a radio tracer95mTcO4-was added to the water. After 4 days incubation of the water, the tracer was separated into four fractions : insoluble, pertechnetate, cationic, and other forms of technetium. On an average, 13% of the95mTcO4-changed to insoluble forms and the maximum ratio of the insolubilization was 76%. This result shows that insolubilization of technetium can occur in the water covering the waterlogged soils. Subsequently, mechanisms of Tc insolubilization were studied using the sample that showed the maximum insolubilization of Tc among the soil samples. When microorganisms were removed from the water by filtration, insoluble forms of Tc decreased to 3.6%. In contrast, the insolubilization ratio increased to 86% by the addition of organic substrates. The insolubilization, therefore, was caused by microorganisms. Furthermore, the addition of antibiotics on bacteria resulted in 23% of the insolubilization, while the antibiotic on fungi did not affect on the insolubilization. If the insolubilization were caused by biosorption, the insolubilization ratio would not decrease for the sample added antibiotics on bacteria. Therefore, these results suggest that the insolubilization of technetium is caused by bioaccumulation of living bacteria. Be-cause the cultures with95mTcO4-were incubated under aerobic conditions, technetium-insolubilizing microorganisms would presumably be aerobic bacteria.
Polystyrene absorbs radon thermodynamically as well as liquid aromatic solvents. We had proposed a new radon measurement using this phenomenon. The measurement, APDLSAbsorptive Polymer Dissolved Liquid Scintillation Counting, is a very easy radon measurement.APDLSfilm that absorbed radon is dissolved in liquid scintillator, and the radioactivity of radon can be measured by liquid scintillation counter. The absorption factor of radon is the radon concentration ratio betweenAPDLSfilm and water. We showed the absorption factor of theAPDLSfilm in table. Radon concentration ofAPDLSfilm divided by the factor is the radon concentration of sample water. This measurement is practicable to radon measurement for environmental research, and has many merits as follows. (1) APDLSmeasurement has no chemical hazard, and is easy to treat. (2) APDLSfilm is easily dissolved in toluene scintillator, and maintains ideal condition for liquid scintillation. (3) The measurement error was less than 5%, and the detection limit was 0.05 Bq Rn/kg water. (4) APDLSfilm is available from Kyoritsu Chemical Check Lab. Co.