Release of Pu isotopes from the Fukushima Daiichi Nuclear Power Plant accident to the marine environment was negligible

Atmospheric deposition of Pu isotopes from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has been observed in the terrestrial environment around the FDNPP site; however, their deposition in the marine environment has not been studied. The possible contamination of Pu in the marine environment has attracted great scientific and public concern. To fully understand this possible contamination of Pu isotopes from the FDNPP accident to the marine environment, we collected marine sediment core samples within the 30 km zone around the FDNPP site in the western North Pacific about two years after the accident. Pu isotopes (239Pu, 240Pu, and 241Pu) and radiocesium isotopes (134Cs and 137Cs) in the samples were determined. The high activities of radiocesium and the 134Cs/137Cs activity ratios with values around 1 (decay corrected to 15 March 2011) suggested that these samples were contaminated by the FDNPP accident-released radionuclides. However, the activities of 239+240Pu and 241Pu were low compared with the background level before the FDNPP accident. The Pu atom ratios (240Pu/239Pu and 241Pu/239Pu) suggested that global fallout and the Pacific Proving Ground (PPG) close-in fallout are the main sources for Pu contamination in the marine sediments. As Pu isotopes are particle-reactive and they can be easily incorporated with the marine sediments, we concluded that the release of Pu isotopes from the FDNPP accident to the marine environment was negligible