A system dynamics model was proposed for investigating the dynamic behavior of fallout 90Sr through production, distribution and consumption of rice, the staple of Japanese food, and the long term accumulation in human bone. The calculated 90Sr contents in rice and human bone were compared with the environmental surveillance data to examine the validity of the model. The results obtained in this study under the limited assumptions are as follows: (1) The proposed model is promising for

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... g the long term behavior of fallout 90Sr in the environment although identification and determination of some environmental parameters should be improved. (2) The migration of fallout 90Sr into the deep soil layers with underground water is most significant among the several transfer pathways considered in the rice-plant field. (3) The influence of rice-crop distribution on the concentration of 90Sr in consumer rice is small. Fallout 90Sr is transported with rice generally from the coast of the Sea of Japan to those of Pacific Ocean. (4) The concentration of 90Sr in rice crops estimated by the proposed model may vary with a factor of 2.5 due to uncertainties in the environmental parameters.