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

Highlights: • Radioactivity monitoring after the FNA was performed in the NSCS from 2011 to 2014. • Radioactivity monitoring was also executed in the LS and its adjacent areas in 2014. • ⁹⁰Sr, ¹³⁷Cs and gross beta in seawater were at the same level before and after FNA. • ¹³⁴Cs in all seawater were not detected after the FNA from 2011 to 2014. • The influence and risk to public health and marine biota from the FNA was negligible. - Abstract: To understand the impact of the Fukushima nuclear accident (FNA), ¹³⁷Cs, ¹³⁴Cs, ⁹⁰Sr, and gross beta were analyzed in the northeast South China Sea (NSCS), the Luzon Strait (LS) and its adjacent areas. ¹³⁷Cs, ⁹⁰Sr, and gross beta values in the NSCS were similar to those prior to the FNA. ⁹⁰Sr and ¹³⁷Cs in the LS and its adjacent areas were consistent with those in the NSCS. 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 ¹³⁷Cs and gross beta mean values in Cruise I were higher than those in Cruise II whereas the ⁹⁰Sr mean value was just the reverse. ¹³⁴Cs in all seawater were below the minimum detectable activity. The past and present data since the 1970s suggested ¹³⁷Cs and ⁹⁰Sr in the study areas still originated from global fallout and the FNA influence were negligible.