Anthropogenic plutonium in the North Jiangsu tidal flats of the Yellow Sea in China.

The (239+240)Pu activities and (240)Pu/(239)Pu atom ratios were analyzed using a double-focusing SF-ICP-MS for sediment core samples obtained in 2007-2008 from the North Jiangsu tidal flats in the Yellow Sea in China. Particular attention was focused on the (240)Pu/(239)Pu atom ratios in the sediment to identify the origins of Pu isotopes. The profiles of (239+240)Pu activities in the sediment cores are similar to those of the (137)Cs activities. The (240)Pu/(239)Pu atom ratios in the tidal flats showed typical global fallout values, indicating that this area did not receive the possible early direct close-in fallout or oceanic current transported Pu from the Pacific Proving Grounds (PPG). If any, the contribution of the PPG source Pu to the total Pu inventory is negligible. This is different from the sediments in the Yangtze River estuary in the East China Sea, where the PPG source Pu contributed ca. 45 % to the total inventory. In addition, the observation of the global fallout origin Pu in the North Jiangsu tidal flats indicated that the nuclear power plant in the region was not causing any alteration/contamination to the (240)Pu/(239)Pu atom ratios. The (239+240)Pu and (137)Cs activities/inventories in the sediment cores showed correlation to the mean clay sediment compositions (fine particles) in the tidal flats. Therefore, mud deposits are served as sinks for the anthropogenic radionuclides in the tidal flats and the Yellow Sea. Integrated with the previously reported spatial distributions of (239+240)Pu and (137)Cs activities in the surface sediments of the Yellow Sea, the mechanism of Pu transport with the ocean currents and the scavenging characteristics in the Yellow Sea were discussed.