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영어

Background: This study was a long-term evaluation of 137Cs and 90Sr activity concentrations in seawater samples from the East Sea, Korea, in order to establish current activity levels. Results and long-term monitoring trends will be useful in the future monitoring of environmental radioactivity. Materials and Methods: Surface seawater samples were collected quarterly from Guryongpo and Jangho in the East Coast between 1998 and 2010 and the quarterly deep seawater samples were collected from three sites in the sea adjacent to Ulleung-do between 2012 and 2015. The activity concentrations of 137Cs were measured using a gamma-spectrometer. The activity concentrations of 90Sr and 90Y in a radioactive equilibrium state were measured using a gas flow proportional counter. Results and Discussion: We found the annual average activity concentrations of 137Cs in the surface seawater was 1.66-2.89 mBq∙kg-1 in Guryongpo and 1.68-2.43 mBq∙kg-1 in Jangho. The annual average activity concentrations of 90Sr in the surface seawater was 0.83- 1.98 mBq∙kg-1 in Guryongpo and 0.82-1.57 mBq∙kg-1 in Jangho. The annual average activity concentrations of 137Cs in the deep seawater sites were 1.51-1.73 mBq∙kg-1, 1.19-1.60 mBq∙kg-1 and 0.87-1.15 mBq∙kg-1 in TH, JD, and HP. The annual average activity concentrations of 90Sr in the same deep seawater sites were 1.00-1.94 mBq∙kg-1, 0.82-1.26 mBq∙kg-1, and 0.79-1.32 mBq∙kg-1. The effective half-life was calculated by analyzing change over time in the activity concentration in the surface seawater. The effective half-life of 137Cs was 15.3 ± 0.1 years in Guryongpo and 102 ± 3 years in Jangho. The effective half-life of 90Sr was 28.3 ± 4.3 years in Guryongpo and 16.6 ± 0.1 years in Jangho. The ratio of the average activity concentration (137Cs/90Sr) was 1.72 in the surface seawater, which is similar to the reported ratio of the global radioactive fallout. The ratio in the deep seawater was 1.24, which is somewhat low compared to the global ratio (1.6, 1.8). Conclusion: Activity concentrations of 137Cs and 90Sr in the seawaters of the East Sea were similar to the previously reported activity levels in the East Sea and northwestern Pacific as a result of global radioactive fallout following atmospheric nuclear weapon tests.