西北太平洋表层海水中239+240Pu浓度及240Pu/239Pu同位素比

钚是与核工业密切相关的敏感元素，是来源于人类核活动、以痕量或超痕量水平存在于环境中的重要锕系元素。与陆地土壤中钚的环境行为不同，输入到海洋环境中的钚会随洋流路径进行远距离迁移扩散。因此，对于包括我国近海在内的西北太平洋区域海水，除受全球沉降影响外，还长期受到美国太平洋核试验场（PPG）所造成区域污染的显著影响。本文利用从相关报道中收集的数据，对西北太平洋表层海水中钚浓度及同位素比的分布特征进行了分析。结果表明，2000年至今，西北太平洋表层海水中^239+240Pu浓度和²⁴⁰Pu/²³⁹Pu同位素比分别在1.15~22.3 mBq/m³和0.184~0.31间变化，其中，^239+240Pu浓度分布与西北太平洋各区域的环境条件等密切相关，而²⁴⁰Pu/²³⁹Pu分布则相对均匀，后者在除中国南海以外的西北太平洋地区均值为0.247±0.025(1σ)，据此估算得美国太平洋核试验场区域污染输入的钚对该海域表层海水中钚的贡献约占其总活度的45%。此外，本文还对福岛核电站附近海域中核事故前后钚的相关数据进行了分析对比，未观察到该事故对西北太平洋海域中钚分布的影响。

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.