Spatial distribution and modelling of Pu in the sediments and seawater columns of the South China Sea and Indian Ocean.

In order to investigate the Pu potential influence in the ocean, and develop a new method for rapidly monitoring radioactive pollution, the Pu spatial distribution in the South China Sea (SCS) and the Indian Ocean (IND) sediments is analyzed by SF-ICP-MS (ELEMENT 2). The inventory-weighted mean activities of Pu were 0.413 ± 0.333 mBq/g, 0.128 ± 0.044 mBq/g, and 0.483 ± 0.606 mBq/g in the sediments of the SCS, eastern IND, and Arabian Sea, respectively. The Pu activity spatial distribution in the SCS sediments was influenced by the current, the vertical distribution of Pu in seawater, and the transport of particulate matter. The Pu activity spatial distribution in the IND sediments could be impacted by Antarctic Intermediate Water. The average of Pu/Pu atomic ratios were 0.258 ± 0.034, 0.219 ± 0.031, and 0.212 ± 0.028 in the sediments of the SCS, eastern IND, and Arabian Sea, respectively. The Pu/Pu atomic ratios in the SCS and IND indicate that Pu from the Pacific Proving Ground (PPG) is transported to the IND via the SCS internal current and transverse ocean currents within Indonesia. In addition, a seawater advection-dispersion equation (S-ADE) model is established based on the actual physical processes of radionuclides in the seawater column and well fitting results were obtained (R = 0.49 to 0.99). The Pu data and the geographic information from the sample site were used to correct the Pu distribution in the seawater. The calculated Pu mean concentrations in the surface seawater were 2.465 mBq/m and 2.205 mBq/m for the SCS and the eastern IND seawater, respectively, and the result is consistent with the previous measurements. Then, the Pu stored in the study area of SCS and eastern IND was estimated to be approximately 1.0-1.4% of the global ocean based on the model. This study provides a useful model for guiding and designing future monitoring of pollution by anthropogenic Pu and other isotopes.