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Transuranium elements such as Np, Pu and Am, are considered to be the most important radioactive elements in view of their biological toxicity and environmental impact. Concentrations of 237Np, Pu isotopes and 241Am in two sediment cores collected from Peter the Great Bay of Japan Sea were determined using radiochemical separation combined with inductively coupled plasma mass spectrometry (ICP-MS) measurement. The 239,240Pu and 241Am concentrations in all sediment samples range from 0.01 Bq/kg to 2.02 Bq/kg and from 0.01 Bq/kg to 1.11 Bq/kg, respectively, which are comparable to reported values in the investigated area. The average atomic ratios of 240Pu/239Pu (0.20 ± 0.02 and 0.21 ± 0.01) and 241Am/239+240Pu activity ratios (3.32 ± 2.76 and 0.45 ± 0.17) in the two sediment cores indicated that the sources of Pu and Am in this area are global fallout and the Pacific Proving Grounds through the movement of prevailing ocean currents, and no measurable release of Np, Pu and Am from the local K-431 nuclear submarine incident was observed. The extremely low 237Np/239Pu atomic ratios ((2.0–2.5) × 10−4) in this area are mainly attributed to the discrepancy of their different chemical behaviors in the ocean due to the relatively higher solubility of 237Np compared to particle active plutonium isotopes. It was estimated using two end members model that 23% ± 6% of transuranium radionuclides originated from the Pacific Proving Grounds tests, and the rest (ca. 77%) from global fallout. [Display omitted] • Distribution of transuranium radionuclides in the sediment cores were investigated. • The contribution of transuranium from PPG was estimated to be 23 ± 6 %. • No measurable release of transuranium from K-431 incident was observed. • 237Np/239Pu atomic ratio might be unsuitable for the source identification. [ABSTRACT FROM AUTHOR]

129 I released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has been observed in the atmospheric, terrestrial and oceanic environments, and it also entered the marine sediments via dispersion by sea water movement and deposition around Japan. However, there have been few studies of marine sediment cores in contrast to the large number of studies on seawater. In this work, a sediment core collected near FDNPP was analyzed for 129 I. It is observed that the 129 I/ 127 I atomic ratios in this sediment core are comparable to those in the seawater and sediments collected from offshore Fukushima after the accident, but 2 orders of magnitude higher than those in seawater in this region before the accident, suggesting the significant amount of 129 I has been transferred and incorporated to the offshore shallow sediments. The difference in environmental behavior between 129 I and 137 Cs is discussed based on their depth distributions in the sediment core in comparison with the grain size distribution of sediments. The peak concentrations of iodine isotopes were found in a relatively deeper layer than radiocesium. Radiocesium follows the distribution of fine grains in the sediment core, implying its high association to fine grains., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The 137 Cs activity in surface water of the East China Sea (ECS) was 0.66-1.36 Bq m -3 during May of 2011. The low activities were observed in the Changjiang Estuary and Zhejiang-Fujian coast and high activities were observed in the south offshore and Kuroshio Current pathway, suggesting that the influence from the current system in the ECS. The 134 Cs were undetectable (<0.03 Bq m -3 ) and the contribution of the Fukushima accident to ECS is estimated to be below 3%; hence it is negligible during the investigation period. Using the vertical profiles of 137 Cs in the ECS, the mass balance is obtained, which suggests that the oceanic input dominates the 137 Cs source in the ECS. 137 Cs is potentially useful to trace water mass movement in the ECS. Our study provides comprehensive baseline of 137 Cs in the ECS for evaluation of the possible influence of the nuclear power plants in the future., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A 30-year-old Japanese cedar (Cryptomeria japonica), collected from Iwaki, Fukushima in 2014, was analyzed for the long-lived radionuclide (14)C. Values of Δ(14)C varied from 211.7‰ in 1984 to 16.9‰ in 2013. The temporal Δ(14)C variation can be described as an exponential decline, indistinguishable from the general Northern Hemisphere Zone 2 (NH Zone 2) values in the atmosphere, until at least 1994. Values of Δ(14)C for 1999 and 2004 are slightly depleted compared with NH Zone 2 values, while from 1999 to 2013 the data suggest a clear depletion with a 2-8 ppmV additional CO2 contribution from a (14)C-free (i.e. fossil carbon) source. This change coincides with local traffic increases since two nearby expressways were opened in the 1990's. In addition, the small but visible (14)C pulse observed in the 2011 tree-ring might be caused by release from the damaged reactors during the Fukushima nuclear accident., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The Fukushima Dai-ichi Nuclear Power Plant accident in 2011 has released a large amount of radionuclides to the atmosphere, and the radioactive plume has been dispersed to a large area in Europe and returned to Asia. To explore long-term trend of the Fukushima-derived radioactive plume and the behavior of harmful radioiodine in the atmosphere, long-term precipitation samples have been collected over 2010-2012 at Fukushima, Japan for determination of long-lived (129)I. It was observed that (129)I concentrations of 1.2 × 10(8) atom/L in 2010 before the accident dramatically increased by ∼4 orders of magnitude to 7.6 × 10(11) atom/L in March 2011 immediately after the accident, with a (129)I/(127)I ratio up to 6.9 × 10(-5). Afterward, the (129)I concentrations in precipitation decreased exponentially to ∼3 × 10(9) atom/L by October 2011 with a half-life of about 29 days. This declining trend of (129)I concentrations in precipitation was interrupted around October 2011 by a new input of (129)I to the atmosphere following a second exponential decrease. Such a cycle has occurred three times until the present. This temporal variation can be attributed to alternating (129)I dispersion and resuspension from the contaminated local environment. A (129)I/(131)I atomic ratio of 16 ± 1 obtained from rainwater samples is comparable with a value estimated for surface soil samples. (129)I results from Denmark suggest an insignificant effect of (129)I released from Fukushima to the (129)I levels in Europe.

The Fukushima nuclear accident in March 2011 has released a large amount of radioactive pollutants to the environment. Of the pollutants, iodine-129 is a long-lived radionuclide and will remain in the environment for millions of years. This work first report levels and inorganic speciation of (129)I in seawater depth profiles collected offshore Fukushima in June 2011. Significantly elevated (129)I concentrations in surface water were observed with the highest (129)I/(127)I atomic ratio of 2.2 × 10(-9) in the surface seawater 40 km offshore Fukushima. Iodide was found as the dominant species of (129)I, while stable (127)I was mainly in iodate form, reflecting the fact that the major source of (129)I is the direct liquid discharges from the Fukushima NPP. The amount of (129)I directly discharged from the Fukushima Dai-ichi nuclear power plant to the sea was estimated to be 2.35 GBq, and about 1.09 GBq of (129)I released to the atmosphere from the accident was deposited in the sea offshore Fukushima. A total release of 8.06 GBq (or 1.2 kg) of (129)I from the Fukushima accident was estimated. These Fukushima-derived (129)I data provide necessary information for the investigation of water circulation and geochemical cycle of iodine in the northwestern Pacific Ocean in the future.