title: Distributions of Pu isotopes in seawater and bottom sediments in the coast of the Japanese archipelago before and soon after the Fukushima Dai-ichi Nuclear Power Station accident.
abstract: A radioactivity measurement survey was carried out from 24 April 2008 to 3 June 2011 to determine the levels of plutonium isotopes and (240)Pu/(239)Pu atom ratios in the marine environments off the sites of commercial nuclear power stations around the Japanese islands; the sampling period extended to two months after the Fukushima Dai-ichi Nuclear Power Station accident. In our previous study (Oikawa et al., 2015), data on Pu isotopes and (241)Am in sediments have already been reported. In this study, we report those on Pu isotopes in seawater as well as sediments, and the characteristics of sediments in addition (e.g., ignition loss and biogenic opals). Concentrations of (239+240)Pu in seawater and bottom sediments remained nearly constant at all sampling locations during the survey period. In addition, no regional differences were observed in the (239+240)Pu concentrations in surface waters. Higher (239+240)Pu concentrations were found in bottom waters at deeper sampling locations, but the (240)Pu/(239)Pu atom ratios were nearly constant regardless of the water depth. Higher (239+240)Pu concentrations were also found in bottom sediments at deeper sampling locations, but vice versa for (240)Pu/(239)Pu atom ratios as reported in the previous report. The sediments samples from deeper locations showed the higher percentage of ignition loss as well as the higher content of biogenic opal. There was likely to be some driving force participating in the transfer of Pu isotopes associated with biogenic substances to the deeper seabed. The present survey showed that the accident at the Fukushima Dai-ichi Nuclear Power Station did not contribute much to the inventory of Pu isotopes in the adjacent sea area.
authors: Central Laboratory, Marine Ecology Research Institute, 300 Iwawada, Onjuku-machi, Isumu-gun, Chiba 299-5105, Japan.
authors: Shinji
authors: S
authors: Oikawa
authors: Head Office, Marine Ecology Research Institute, Towa-Edogawabashi Bldg. 7F., 347 Yamabuki-cho, Shinjuku, Tokyo 162-0801, Japan.
authors: Teruhisa
authors: T
authors: Watabe
authors: Central Laboratory, Marine Ecology Research Institute, 300 Iwawada, Onjuku-machi, Isumu-gun, Chiba 299-5105, Japan. Electronic address: takata@kaiseiken.or.jp.
authors: Hyoe
authors: H
authors: Takata
mesh_terms: D062406:Fukushima Nuclear Accident; D019015:Geologic Sediments / Q000737:chemistry*; D007564:Japan; D011005:Plutonium / Q000032:analysis*; D011834:Radiation Monitoring; D012623:Seawater / Q000737:chemistry*; D013997:Time Factors; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D014875:Water Pollutants, Radioactive; D011005:Plutonium
keywords: (240)Pu/(239)Pu; Biogenic opal; Global fallout; Ignition loss