The distributions of 134Cs, 137Cs and 90Sr in the northwest Pacific seawater in the winter of 2012.

To understand the status of the radionuclides released during the Fukushima Dai-ichi Nuclear Power Plant accident, the 134Cs, 137Cs and 90Sr in the seawater in the public area of the northwest Pacific Ocean were analyzed in November-December 2012. The radioactivity of 134Cs, 137Cs and 90Sr decreased sharply from June 2011 to November-December 2012. The highest average values of 134Cs and 137Cs were found at a depth of 500 m, suggesting that 134Cs and 137Cs had been transported to a depth of 500 m or deeper by the end of 2012. Total inventories of 0.80 ± 0.20 pBq for 137Cs from the surface to a depth of 500 m and 0.07 ± 0.02 pBq for 90Sr from the surface to a depth of 100 m were obtained in the waters southeast of Fukushima. 134Cs was detectable in the Chinese exclusive economic zone, and the seawater quality was much lower than the target level for China.