Determination of carbon spices formed by decomposition of acetate in Japanese paddy soil

Office of Biospheric Assessment for Waste Disposal, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba-shi, Chiba 263-8555, Japan

Abstract

For appropriate safety assessment of TRU waste disposal, the dominant chemical species of ¹⁴C-gas was studied. [1,2-¹⁴C] sodium acetate was added to flooded paddy soil samples, and the content of ¹⁴C in the soil, solution, and the emitted CO₂ gas during incubation period was determined. Recovery ratios of the total ¹⁴C activity to the initial ¹⁴C activity were 97.9% at day 1, 86.4% at day 3, and 83.5% at day 7 of incubation. The result of the day 1 means that the emitted ¹⁴C-gas was almost ¹⁴CO₂. At day 7 of incubation, about 16.5% of ¹⁴C was failed to recover. Even if the unknown ¹⁴C was gases other than ¹⁴CO₂, the dominant chemical species of the emitted ¹⁴C-gas will be ¹⁴CO₂, because the recovery ratio of the ¹⁴CO₂ was 48.9% (¿16.5%). Sodium 2-bromoethane-sulfonate was used to ensure the emission of CH₄, but there was no effect of the regent to the recovery ratio of ¹⁴CO₂. Methane emission may be little under our experimental conditions. These results suggest that the dominant chemical species of the emitted ¹⁴C-gas from the flooded paddy soil samples was ¹⁴CO₂.