日本近海における^<137>Csの消長および水産食品摂取による被ばく線量の推定に関する研究

概要

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The relationship between the flux of the atmospheric 137Cs at the surface of the seas and its concentration in seawater was studied to elucidate its fate in the marine environment and to assess the radiological effects on the human population. In this context, a simplified mathematical model that expressed the time course of the concentration in the first order of kinetics was introduced, and the parameters involved in the formula were numerically derived for three regions of the coastal sea of Japan by a regression analysis from a series of radioactivity survey data reported over the past 30 years since 1960. It is expected that 137Cs was retained in the coastal sea of Japan with a half-life period ranging from 5.3 to 6.8 years without a great difference between the Pacific Ocean and the Sea of Japan. The integrated concentrations of 137Cs in seawater were determined as 0.191, 0.173, and 0.120mBq·a/l, respectively, for the coasts of Ibaraki/Fukushima, Niigata, and Fukui prefectures as a result of the deposition at a unit density (1MBq/km2). The resultant dose commitment to the respective populations would amount to 4.5, 2.4, and 0.9×10-3man·Sv through coastal fishery products.