Radioactive status of seawater and its assessment in the northeast South China Sea and the Luzon Strait and its adjacent areas from 2011 to 2014

To understand the impact of Fukushima Nuclear Accident (FNA), many campaigns were performed in the northeast South China Sea (NSCS) as well as Luzon Strait (LS) and its adjacent areas from 2011 to 2014. The radioactive status of 137Cs, 134Cs, 90Sr and gross beta in seawater was reported after the FNA. 137Cs, 90Sr, and gross beta values in the surface seawater in NSCS were at levels similar to those prior to the FNA. Additionally, 90Sr and 137Cs in the LS and its adjacent areas during the two cruises in 2014 were consistent with those in the NSCS, nevertheless gross beta in the LS and the west Pacific area in 2014 were slightly higher than those in NSSC (2011-2014). From west to east along the LS, the mean values of gross beta activities seem to be gradually on the rise from the South China Sea to the west Pacific ocean. The high 137Cs-peak values occurred at depth of 150 m whereas the high 90Sr-peak values occurred at depth of 0.5 m. The mean values of 137Cs and gross beta special activities in Cruise I were higher than in Cruise II, whereas the mean values of 90Sr activity were found to be lower in the LS and its adjacent areas. In this study, 134Cs in all seawater were below MDA.134Cs in all seawater were below the MDA. Based on past and present data since the 1970s, it was concluded that 137Cs and 90Sr in the SSCS, the LS and its adjacent areas should still originate from global fallout, and the influence and risk to public health and marine biota from the FNA were negligible.283