For appropriate safety assessment of TRU waste disposal, gasification ratios and distribution coefficients (Kd) of 14C labeled [1, 2-14C] sodium acetate were determined by batch experiments for a Japanese paddy soil sample. Approximately 60% of the total added C-14 was released from the flooded paddy soil into the air as gas forms during 7 days shake-incubation periods. In the present study, the paddy soil was contacted with deionized water and well water, and the lower gasification ratio was found for the well water sample. The similar result was observed for the Kd values. Values of Kd varied from 51 to 138 mL g-1. The lower values were observed when the soil was contacted with well water. When the microorganisms in the samples were killed by glutaraldehyde, both gasification ratios and Kd values were nearly zero. These results suggested that microorganisms responsible for the behavior of C-14 in biosphere. In addition, water characteristics such as dissolved ions, pH and electrical conductivity would affect the gasification ratio and the Kd values.