Impacts of the Fukushima nuclear accident on the China Seas: Evaluation based on anthropogenic radionuclide 137Cs

Abstract

In order to evaluate the impact of the Fukushima nuclear accident on the China Seas, seawater samples from the South China Sea (SCS), the East China Sea (ECS) and the Yellow Sea (YS) were collected in April–June 2011, and their 137 Cs activities were measured using low-background γ-spectrometry. 137 Cs activities in the study area ranged from 0.75±0.07 to 1.43±0.08 Bq m −3 with an average of 1.12±0.08 Bq m −3 . 137 Cs activities initially increased from the nearshore to the inner shelf, and subsequently decreased from the inner shelf to the outer shelf. Vertical profiles showed higher 137 Cs activities at the surface but lower activities at depth in the ECS, suggesting atmospheric input of 137 Cs. As such, the distribution pattern of 137 Cs in the region was presumably determined by a combination of atmospheric deposition and subsequent mixing between different water masses including the coastal currents, the Yangtze River plume and the Taiwan Warm Currents. Based on the inventory of 93 Bq m −2 and the atmospheric deposition flux of 137 Cs in the ECS of 32.2 mBq m −2 d −1 (5.4–42.9 mBq m −2 d −1 ) which we estimated, we derived the residence time of 137 Cs in the upper water column to be 66 d (45–95 d). We concluded that in terms of 137 Cs, the ECS was less impacted by the Fukushima accident as compared to the Chernobyl accident. The released amount of 137 Cs into the ECS from the Fukushima accident was minute.