Pu239+240 concentrations and Pu-240/Pu-239 atom ratios in bottom sediments of the Yellow Sea, Korea Strait, East Sea (Sea of Japan), Sea of Okhotsk, and Northwest Pacific Ocean were determined. In coastal sediments near the Korean Peninsula, Pu239+240 concentrations varied from 0.02 to 1.72 Bq.kg(-1), and their Pu-240 /Pu-239 atom ratios from 0.15 to 0.24, with an average of 0.20+/-0.03. Pu-240/Pu-239 atom ratios of bottom sediments in the deep NW Pacific Ocean and its marginal seas(East,Okhotsk seas) were in the range of 0.15-0.23. A little elevated Pu-240/Pu-239 atom ratios in the bottom layer sediment may be due to Pu released into the environment during the pre-moratorium period, having high Pu-240 /Pu-239 atom ratios and low Pu-238/Pu239+240 activity ratios.
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