^239+240Pu Concentration and ²⁴⁰Pu/²³⁹Pu Isotopic Ratio in Surface Seawater of Northwest Pacific

Plutonium is a sensitive element closely related to nuclear industry. It is an important actinide element originated from human nuclear activities and exists in the environment at trace or ultra trace levels. Different from the behavior of plutonium in the terrestrial environment, plutonium entered into the marine environment could be driven by ocean currents and then transported for a long distance. In addition to the global subsidence, the sea water in the Northwest Pacific region, including China’s coastal waters, is significantly affected by the regional pollution caused by the US Pacific Proving Ground (PPG) for a long time. With data assembled from published articles, the distributions of Pu concentration and isotopic ratios in surface seawater of Northwest Pacific were analyzed in this work. After 2000, ^239+240Pu concentration and ²⁴⁰Pu/²³⁹Pu isotopic ratio in surface seawater of this region vary in 1.15-22.3 mBq/m³ and 0.184-0.31, respectively. The spatial distribution of ^239+240Pu concentration is closely related to local environmental conditions, while that of ²⁴⁰Pu/²³⁹Pu isotopic ratio is rather more homogeneous. Despite the China South Sea, the mean value of ²⁴⁰Pu/²³⁹Pu isotopic ratio for Northwest Pacific Ocean is 0.247±0.025(1σ). According to that, the contribution of Pu from PPG is estimated to be around 45% in surface seawater. In addition, Pu data in marine environment off Japan Fukushima Dai-chi Nuclear Power Plant were also collected and compared, among which no indication of Pu released from the accident could be observed.