The Transition and Distribution of 90Sr and 137Cs Concentrations in Fukuoka Prefecture (1989-2000)

This paper summarizes the distribution and concentration of 90Sr and 137Cs fallout in the natural environment (deposition, soil, total diet, service water, seawater and sea sediment) of Fukuoka Prefecture, and related transition during the period from 1989 to 2000. The 90Sr and 137Cs concentrations respectively showed a gradual decrease over the timeframe; especially, 90Sr deposition has not been detected since 1997, while 137Cs has been detected rarely. Both radionuclides had accumulated in the soil at comparatively high concentrations for a long period of time; the average concentrations of 90Sr and 137Cs in the upper 5-cm soil layer were 5.3Bq/kg dry and 6.0Bq/kg dry, respectively. Their concentrations in the total diet were significantly different between the urban districts and fishing villages, mainly depending on the contents of the meals. No significant difference was observed in 90Sr concentration when comparing fresh water and seawater. 137Cs was detected in seawater, but not in fresh water. On the other hand, 137Cs was detected in sea sediment, but 90Sr was not. These observations suggest that there is a remarkable difference in the behavior of each nuclide in the environment.