Anthropogenic radionuclides in seawater in the East Sea Japan Sea: Resultsof the first-stage Japanese-Korean-Russian expedition

Measurements of anthropogenic radionuclides in seawater samples near dumpin g sites of the East Sea/Japan Sea were conducted, as the first-stage Japane se-Korean-Russian Joint Expedition, in March-April 1994, to assess radioact ive contamination of the East Sea/Japan Sea after the dumping of radioactiv e wastes by the former Soviet Union and Russian Federation. Concentrations of Cs-137, Sr-90 and Pu-239,Pu-240 in surface waters of the East Sea/Japan Sea near dumping sites were in the ranges of 2.8-3.6,1.6-2.0, and 8-25 Bq k g(-1), respectively. Surface Cs-137 and Sr-90 concentrations were the same order of magnitude as those observed in the North Pacific, whereas surface Pu-239,Pu-240 concentration was significantly higher than those observed in the North Pacific. Vertical profiles of Cs-137 and Sr-90, with surface max ima and decreasing with depth, showed higher depth gradients than those obs erved in the North Pacific, reflecting deep convection in the north central East Sea/Japan Sea. The higher Pu-239,Pu-240 concentration in the surface waters of the north central East Sea/Japan Sea may reflect rapid recycling of deep Pu. The results revealed that most of the recent radioactivity obse rved in the north central East Sea/Japan Sea was of global fallout origin f rom atmospheric nuclear testing and partly the Chernobyl fallout. In this s urvey, there was no clear evidence of an increase in radionuclide concentra tions due to the dumping of radioactive wastes by the former Soviet Union a nd Russian Federation. (C) 1999 Elsevier Science Ltd. All rights reserved.