No long-term variation of 240Pu/239Pu atom ratio in liver of Japanese common squid (Todarodes pacificus) collected from seven sea areas around Japan during 2003-2018.

The 239+240Pu concentrations and 240Pu/239Pu atom ratios were determined to trace the temporal variability in concentration and atom ratio in liver of the Japanese common squid during 2003-2018. The differences in their concentrations and atom ratios and the dependency on the collection areas and migratory history were compared. The organ affinity of Pu in mantle, limb, liver, and internal organs except liver was also investigated. The average 239+240Pu concentrations were the highest in liver followed in order by internal organs except liver, limb, and mantle. The Pu accumulation in liver could be explained by a mechanism for foreign substance processing. A significant difference in the average 239+240Pu concentrations in liver was found among the sea areas for specimen collection during 2003-2018. In spite of a noticeable difference in the average 239+240Pu concentrations, the 240Pu/239Pu atom ratios showed no significant temporal variability around Japan; thus, they were continuously uniform during 2003-2018.

Aplastic Anemia with Epstein-Barr Virus Reactivation after Anti-thymocyte Globulin Therapy.

Lymphoproliferative disorders and Epstein-Barr virus reactivation (EBV-LPDs) have various forms of onset, ranging from infectious mononucleosis-like syndrome (IM-like) to lymphoma, although whether or not IM-like progresses to lymphoma remains unclear. A 61-year-old man was diagnosed with aplastic anemia (AA). Polyclonal atypical B-lymphocytes were observed in the peripheral blood, and IM-like was diagnosed. Atypical lymphocytes disappeared, but a gastrointestinal examination revealed diffuse large B-cell lymphoma (DLBCL). Rituximab was initiated but later discontinued because of severe acute respiratory syndrome coronavirus 2 infection. Pancytopenia due to AA exacerbation recurred. The patient ultimately died of multiple organ failure due to bacterial infection.

[Enhancement of Antitumor Effect by the Combined Use of Anti-EGFR Antibody(Necitumumab)and PD-1 Inhibitor].

Necitumumab enhances antitumor immunity by decreasing the PD-L1 expression; it is expected to improve the prognosis of patients treated with an immune checkpoint inhibitor(ICI)by inhibiting the IL-8 expression. Since the combined effect of necitumumab and PD-L1 inhibitor was confirmed in an in vivo study conducted in transgenic mice, further antitumor effects can be expected by the combined use of necitumumab and ICI.

Enhanced boundary scavenging of 241Am on the continental margin of the East China sea.

The 241Am concentrations were determined by sector field high-resolution inductively coupled plasma mass spectrometry for settling particles and surface sediments collected on the continental margin in the East China Sea to discuss the behavior of 241Am in the studied area. A large and regular increase was noted from 97 m depth to 592 m depth in 241Am concentrations in settling particles from the cylindrical sediment traps, whereas only a slight increase in 239+240Pu concentrations was evident. The gradual increase in 241Am/239+240Pu activity ratios from the cylindrical trap settling particles also was observed. These results were attributed to 241Am being scavenged by settling particles at a more rapid scavenging rate than 239+240Pu. There was an obvious tendency for 241Am fluxes to increase linearly with depth with the highest fluxes at near-bottom, and these fluxes were due to large advective import to the near-bottom. There was a tendency for 241Am concentrations in surface sediments to increase almost linearly with depth, showing the same tendency as 210Pb concentrations, and this tendency indicated that the enhanced boundary scavenging of 241Am as well as 210Pb occurred in the East China Sea continental slope region due to the greater abundance of reactive finer particles. The 241Am concentrations in settling particles from the time-series sediment trap ranged from 1.05 to 4.20 mBq g-1, showing large variation. The 241Am concentrations from the time-series trap varied inversely with the total mass fluxes, indicating that 241Am concentrations were diluted by particles when mass flux increased. The 241Am fluxes showed large time-series variations and these variations were primarily controlled by mass flux variation. It seems that the high total mass flux events are due to resuspension of the underlying surface sediments and episodic lateral transport of particles that flow down the continental slope in the East China Sea.

Cesium-137 and 137Cs/133Cs atom ratios in marine zooplankton off the east coast of Japan during 2012-2020 following the Fukushima Dai-ichi nuclear power plant accident.

We measured the concentrations of cesium isotopes (133Cs, 134Cs, and 137Cs) in zooplankton samples collected in waters off the east coast of Japan from May 2015 to June 2020. By combining these data with those obtained previously from May 2012 to February 2015, we evaluated the long-term impacts of the Fukushima Dai-ichi Nuclear Power Plant accident on marine zooplankton. Relatively high 137Cs concentrations in zooplankton, exceeding 10 Bq/kg-dry weight, were sporadically observed until June 2016, regardless of year or station. After May-June 2017, 137Cs concentrations decreased to below 1 Bq/kg-dry at most stations, and by May 2020, concentrations were below 0.5 Bq/kg-dry except those off Fukushima Prefecture. Since the accident, the 137Cs/133Cs atom ratios of zooplankton samples were higher than those of ambient seawater until 2019, but in May-June 2020 the ratios matched those of seawater except off Fukushima Prefecture. Highly radioactive particles were not detected in zooplankton samples by autoradiography using imaging plates after May-June 2017, although they were before. Therefore, the persistence of elevated 137Cs/133Cs ratios in zooplankton relative to seawater for nine years after the accident was probably due to the incorporation of highly radioactive particles (cesium-bearing particles or clay-mineral aggregates with highly adsorbed radiocesium) onto/into zooplankton for several years after the accident. However, since at least May-June 2017, these elevated ratios have likely been caused by small highly radioactive particles (or larger particles disaggregated into small pieces) entering the ocean from land via rivers or directly discharged from the Fukushima Nuclear Power Plant. Microplastics enriched with radiocesium with higher 137Cs/133Cs ratios than seawater may have also contributed 137Cs to the zooplankton.

Multiple Evaluation of Typical Heavy Metals Pollution in Surface Soil and Road Dust from Beijing and Hebei Province, China.

Soil and road dust are important receptors of heavy metals in the environment. Meanwhile, heavy metal could transfer to the atmosphere through resuspension. Due to the serious consequences and atmospheric haze in Jing-Jin-Ji area, it's important to evaluate the pollution level, particle size distribution and sources of heavy metals. For heavy metals in soil samples, similar concentrations to the background values and no obvious pollution or low-level pollution was presented. Higher concentration of Cu (78.9 mg/kg) and Zn (261 mg/kg) were found in road dust. The source appointment results showed that Mn, Co, Cr, Ni, Zn and Pb in soils and Cr, Co and Mn in road dust were mainly from the natural sources, while traffic source contributed to most of Cu, Zn and Pb in road dust. Different particle size distribution patterns were found in soils and road dusts, and the finest particles presented the highest heavy metal concentrations.

Fifty-Six Years after Acrylic Hemiarthroplasty and after Then: A Case Report of Revision THA.

We revised an acrylic femoral hip prosthesis to a total hip prosthesis for an 86-year-old female. The implant was made of dental resin and had functioned for 56 years in situ, though its stem had broken. Because of no osteolytic reaction, the reconstruction was relatively easy. From the result of histologic and radiologic examination, the bio-inertness of material and uncemented fixation seemed to contribute the minimum bone loss and to the favorite spontaneous arthrodesis after providing good joint function in her middle age.

Assessment of chromosome aberrations in large Japanese field mice (Apodemus speciosus) in Namie Town, Fukushima.

PURPOSE: After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in Japan on March 11 2011, the surroundings became contaminated with radionuclides. To understand the possible biological effects after chronic low dose-rate radiation in contaminated areas of Fukushima, we assessed the effects in large Japanese field mice (Apodemus speciosus) by means of chromosome aberration analysis. MATERIALS AND METHODS: We collected A. speciosus in five sites around Namie Town, Fukushima (contaminated areas) and in two sites in Hirosaki City, Aomori (control areas, 350 km north of FDNPP) from autumn 2011 to 2013. The number of mice captured and ambient dose-rates were as follows: high (n = 11, 10.1-30.0 µGy h-1), moderate (n = 10, 5.7-15.6 µGy h-1), low (n = 12, 0.23-1.14 µGy h-1) and control (n = 20, 0.04-0.07 µGy h-1). After spleen extraction from rodents, spleen cell culture was performed to obtain metaphase spreads. Chromosome aberrations were assessed on Giemsa-stained metaphase spreads. RESULTS: Although the mice in the contaminated areas were chronically exposed, there was no radiation-specific chromosome aberrations observed, such as dicentric chromosomes and rings. Some structural aberrations such as gaps and breaks were observed, and these frequencies decreased annually in mice from Namie Town. CONCLUSION: These findings suggest that chromosome aberration analysis is useful to evaluate and monitor radiation effects in wild animals.

A storm-induced flood and associated nearshore dispersal of the river-derived suspended 137Cs.

Accidental leakage of radionuclides from the Fukushima Nuclear Power Plant (FNPP1) took place in the aftermath of the catastrophic tsunamis associated with the Great East Japan Earthquake that occurred on March 11, 2011. Significant amount of radionuclides released into the atmosphere were reportedly transported and deposited on land located near FNPP1. The Niida River, Fukushima, Japan, has been recognized as a terrestrial source of highly contaminated suspended radiocesium adhering to sediment particles in the ocean through the river mouth as a result of hydrological processes. Remaining scientific questions include the oceanic dispersal and inventories of the sediments and suspended radiocesium in the ocean floor derived from the Niida River. Complementing limited in situ data, we developed a quadruple nested 3D ocean circulation and sediment transport model in an extremely high-resolution configuration to quantify the transport processes of the suspended radiocesium. Particularly, we investigated the storm and subsequent floods associated with Typhoon 201326 (Wipha) that passed off the Fukushima coast in October 2013, and subsequently promoted precipitation to a considerable extent and associated riverine freshwater discharge along with sediment outfluxes to the ocean. Using in situ bed sediment core data obtained from regions near the river mouth, we conducted a quantitative assessment of the accumulation and erosion of the sediments and explored the resultant suspended radiocesium distribution around the river mouth and nearshore areas along the Fukushima coast. We identified three major accumulative areas, near the river mouth within an area < 1 km, around the breakwaters in the north of the river mouth, and along the southern coastal area, while offshore and northward transports were minor. The present study clearly exhibits substantial retention of the land-derived radiocesium adsorbed to the sediments in the coastal areas, leading to possible long-term influences on the surrounding marine environment.

Temporal trend of 240Pu/239Pu atom ratios in water columns in the Western North Pacific Ocean and its marginal seas.

The 240Pu/239Pu atom ratios were determined by inductively coupled plasma mass spectrometry for seawater samples from the Okinawa Trough in the western North Pacific Ocean margin to identify their Pu sources and to elucidate the temporal variability in atom ratios in the water columns in the western North Pacific Ocean and its marginal seas. The 239Pu, 240Pu and 239+240Pu water column inventories were 12.2 ± 0.5, 10.5 ± 0.5 and 22.7 ± 0.7 Bq m-2, respectively. The observed 240Pu/239Pu ratios were clearly greater than the mean global fallout ratio of ∼0.18 with a mean value of 0.236 ± 0.014. The observed greater atom ratios confirmed the presence of close-in fallout Pu from nuclear testing at the Pacific Proving Grounds (PPG). The relative percentage of the PPG-derived Pu to global fallout Pu was estimated as 41 ± 10%. The 239+240Pu water column inventory originating from the PPG close-in fallout was also calculated as 9.2 ± 0.4 Bq m-2. The temporal variability in the mean 240Pu/239Pu atom ratios in the water columns in the western North Pacific Ocean and its marginal seas was obtained through comparison of the present study values and the previously reported values, and it had no significant temporal variation with a mean value of 0.237 ± 0.004 during the observation period of 1984-2015. The 239Pu and 240Pu derived from the two different sources of global fallout and the close-in fallout at the PPG were homogenized in the water masses in the studied areas.

Distributions of 239Pu and 240Pu Concentrations and 240Pu/239Pu Atom Ratios and 239+240Pu Inventories in a Water Column in the Eastern Indian Ocean: Transport of Pacific Proving Grounds-Derived Pu via the Indonesian Throughflow.

The 239+240Pu concentrations and 240Pu/239Pu atom ratios in seawater from the eastern Indian Ocean were determined to identify their Pu sources and to propose the transport pathway of Pacific Proving Grounds (PPG)-derived Pu into the studied area. This is the first study by anyone on these Pu atom ratios in the Indian Ocean. In the West Australia Basin, the 239+240Pu concentration was 2.89 mBq m-3 in the surface water and increased with depth; a subsurface maximum was identified at 200 m depth and then decreased gradually with depth; its water column inventory was 32.8 Bq m-2. The inventory-weighted mean 240Pu/239Pu atom ratios were 0.208 in the South Australia Basin, 0.226 in the Perth Basin, 0.242 in the West Australia Basin, 0.232 in the Bay of Bengal, and 0.225 in the Andaman Sea. The obtained 240Pu/239Pu ratios were clearly greater than the mean global fallout ratio of 0.18. These high atom ratios proved the presence of close-in fallout Pu from PPG nuclear tests. The relative contribution of global and PPG fallouts was evaluated using the two-end-member mixing model. The 239+240Pu inventories originating from the PPG fallout were calculated as 2.9-14.9 Bq m-2, which corresponded to 20-46% of the total 239+240Pu inventory. A significant amount of the PPG-derived Pu has been transported to the eastern Indian Ocean. The proposed transport pathway accounting for the high 240Pu/239Pu ratio is the transportation of PPG-derived Pu by the North Equatorial Current followed by the Mindanao Current, Indonesian Throughflow, and then spreading over the Indian Ocean by its surface circulation system.

Effects of environmental conditions, low-level potassium, ethylenediaminetetraacetic acid, or combination treatment on radiocesium-137 decontamination in Napier grass.

Phytoextraction is widely used to remove environmental pollutants such as heavy metals or radionuclides from soil. It is important to understand how to enhance the accumulation of contaminants by plants. Previously, we found that Napier grass (Pennisetum purpureum Schum.) has the potential to effectively remove Cs (133Cs and 137Cs). In order to enhance the remediation efficiency of Napier grass, we evaluated the effects of low-level K (K), ethylenediaminetetraacetic acid (EDTA), or the combination of low-level K and EDTA (K+EDTA). We also examined the differences in 137Cs decontamination between two cropping years (2018 and 2019). Overall, there were no prominent effects from the K, EDTA, or K+EDTA treatments on plant growth (plant height, tiller number), aboveground biomass, 137Cs concentration, and 137Cs removal ratio (CR) in 2 years. However, the aboveground biomass (P < 0.001), 137Cs concentration (P < 0.001 in 2019 only), and CR (P < 0.001) in plants grown in the first growing period were significantly higher than in plants grown in the second growing period in both years. The mean 137Cs concentration (P < 0.001) and total CR (P < 0.001) per year was significantly greater in 2019 than in 2018. The precipitation amount during the cultivation period in 2019 (1197 mm) was 1.8-fold higher than in 2018 (655 mm). In this study, the K, EDTA, and K+EDTA treatments had less effect plant growth than the natural environmental conditions. To enhance remediation efficiency, soil moisture is one important factor to produce more aboveground biomass to achieve high CR in Napier grass.

Highly Enantioselective Direct Asymmetric Reductive Amination of 2-Acetyl-6-Substituted Pyridines.

A highly direct asymmetric reductive amination of a variety of ketone substrates, including 2-acetyl-6-substituted pyridines, ß-keto esters, ß-keto amides, and 1-(6-methylpyridin-2-yl)propan-2-one, has been disclosed for the first time (94.6% to >99.9% ee). With ammonium trifluoroacetate as the nitrogen source, various chiral corresponding primary amines were prepared in excellent enantioselectivity and conversion in the presence of a commercially available and inexpensive chiral catalyst, Ru(OAc)2{(S)-binap}, under 0.8 MPa of hydrogen gas pressure.

Transition of Radioactive Cesium Deposition in Reproductive Organs of Free-Roaming Cats in Namie Town, Fukushima.

We investigated the internal contamination by radioactive cesium associated with the FDNPP accident, in the testes or uterus and ovaries of free-roaming cats (Felis silvestris catus), which were protected by volunteers in the Namie Town, Fukushima. A total of 253 samples (145 testes and 108 uterus and ovaries) obtained from adult cats and 15 fetuses from 3 pregnant female cats were measured. Free-roaming cats in Namie Town had a higher level of radioactive contamination in comparison to the control group in Tokyo, as the 134Cs + 137Cs activity concentration ranged from not detectable to 37,882 Bq kg-1 in adult cats. Furthermore, the radioactivity in the fetuses was almost comparable to those in their mother's uterus and ovaries. The radioactivity was also different between several cats protected in the same location, and there was no significant correlation with ambient dose-rates and activity concentrations in soil. Moreover, radioactive cesium levels in cats decreased with each year. Therefore, it is likely that decontamination work in Namie Town and its surroundings could affect radioactive cesium accumulation, and thus possibly reduce the internal radiation exposure of wildlife living in contaminated areas. It is hence necessary to continue radioactivity monitoring efforts for the residents living in Namie Town.

Background and fingerprint characteristics of anthropogenic 236U and137Cs in soil and road dust samples collected from Beijing and Zhangjiakou, China.

236U has attracted more attention as an environmental tracer in recent years. However, in-depth study of 236U in terrestrial environments is still rare in China. Data on 236U and 137Cs concentrations in soil and road dust samples collected from Beijing and Zhangjiakou, China were obtained to demonstrate the background and distinct characteristics of anthropogenic 236U and 137Cs. 236U and 137Cs were detected in the range of (1.10-7.90) × 107 atoms g-1 and below the method limits of detection to 5.30 Bq kg-1. A clear characteristic was observed in road dust, where 236U concentrations increased with decreasing of sample particle size. Soil samples showed an irregular characteristic, but the highest 236U concentrations were observed in particle size fraction of <0.053 mm in both samples. This phenomenon was caused by U chemical properties, higher specific surface areas and organic compounds in fine particles. Anthropogenic radionuclides fingerprint characteristics in <0.053 mm samples were specially discussed. 236U/238U atom ratios were detected in the range of (0.627-3.38) × 10-8. A weak correlation between anthropogenic 236U and natural U isotopes were observed. The intermediate correlation between 236U and 137Cs indicated somewhat distinct migration behavior of these two radionuclides in soil after release to the environment. The released amount of 236U from global fallout during the period of atmospheric nuclear weapons testing was roughly estimated to be 1300 ± 448 kg. These results could be used as fingerprint information for anthropogenic 236U migration behavior and tracer application in environment.

Transuranic nuclides Pu, Am and Cm isotopes, and 90Sr in seafloor sediments off the Fukushima Daiichi Nuclear Power Plant during the period from 2012 to 2019.

The 238Pu, 239+240Pu, 241Am, 242Cm, 243+244Cm and 90Sr concentrations in seafloor surface sediments collected at three sampling stations off the Fukushima Daiichi Nuclear Power Plant (FDNPP) site during the period from 2012 to 2019 were determined to elucidate the impacts of the FDNPP accident onto their concentrations in coastal sediments and to discuss the sources of the measured radionuclides. The 239+240Pu, 241Pu and 241Am concentrations and 240Pu/239Pu atom ratios in a sediment core were also determined to allow comparison of their inventories between this study and previously reported values and to identify the Pu sources. The 238Pu, 239+240Pu, 241Am and 90Sr concentrations showed no remarkable temporal variations; no significant increases in concentrations after the FDNPP accident were observed; these concentrations were comfortably within the previously reported concentration range; and no detectable 242Cm and 243+244Cm amounts were observed in surface sediments. The observed 238Pu/239+240Pu activity ratios were approximately two orders of magnitudes lower than those for the damaged FDNPP reactor core inventories and the observed values in terrestrial samples after the accident. The 239+240Pu, 241Pu and 241Am inventories in the sediment core were 389 ± 5, 503 ± 33 and 214 ± 3 Bq m-2, respectively. The 239+240Pu inventory was about an order of magnitude greater than the expected cumulative deposition density of global fallout from atmospheric nuclear weapons testing due to an enhanced scavenging effect. The 240Pu/239Pu atom ratios in the sediment core ranged from 0.239 to 0.246 with a mean value of 0.242 ± 0.002; these ratios were clearly greater than the mean global fallout ratio of 0.18. The results for 238Pu/239+240Pu activity ratios and 240Pu/239Pu atom ratios reflected a mixture of global fallout and Pacific Proving Grounds (PPG) close-in fallout Pu rather than Fukushima accident-derived Pu. The sediment column inventory for 239+240Pu originating from the PPG close-in fallout was calculated as 166 Bq m-2, which corresponded to 43% of the total inventory. A significant amount of the PPG-derived Pu has been transported by ocean currents and then preferentially scavenged in the coastal waters of Japan.

Temporal variation of iodine-129 concentrations in kelps (Saccharina) from coastal waters off northern Japan.

Concentrations of 129I and 127I in kelps (Saccharina) collected from coastal waters off northern Japan were monitored from 2007 to 2019. During the 2007-2008 test operation of the Rokkasho nuclear fuel reprocessing plant, 129I discharge from the plant increased, and the 129I concentration and 129I/127I atom ratio in the kelps reached maxima of 42 µBq/g-dry and 264 × 10-11, respectively. By 2009, both had decreased by one order of magnitude. After the Fukushima Dai-ichi Nuclear Power Plant accident in 2011, the 129I concentration and 129I/127I atom ratio in the kelps increased to 2.24 µBq/g-dry and 11.6 × 10-11, respectively. After 2012, the ratio in kelps decreased to (2.1-8.9) × 10-11, which is almost the same as the seawater value off Aomori Prefecture before the test operation. The 129I/127I atom ratio in kelps thus represents the ambient seawater ratio during the growth period of the kelps.

[Intradural Mucocele Associated with a Frontoethmoidal Osteoma:A Case Report].

The formation of symptomatic intradural mucocele associated with a paranasal osteoma is rare, and no standard treatment has been established. Here, we present a case of intradural mucocele in a 27-year-old man complaining of headache and generalized convulsion. Cranial CT and brain MRI showed a left frontoethmoidal osteoma extending into the left anterior cranial fossa and orbit along with a mass in the left frontal lobe. He underwent resection of both intracranial osteomas and the mass through left frontal craniotomy. Histological findings were consistent with a mucocele, and the diagnosis of an intradural mucocele associated with a frontoethmoidal osteoma was confirmed. The postoperative course was uneventful. Although both osteoma and mucocele are benign, they may cause life-threatening symptoms by expanding intracranially. A tailored treatment considering the invasiveness and postoperative long-term follow-up of the patient is essential for this uncommon condition.

240Pu/239Pu atom ratios in water columns from the North Pacific Ocean and Bering Sea: Transport of Pacific Proving Grounds-derived Pu by ocean currents.

The 240Pu/239Pu atom ratios in seawater from the northern North Pacific Ocean and Bering Sea were determined to elucidate the temporal variability in 239+240Pu inventory, to identify their Pu sources and to propose the transport pathway of Pacific Proving Grounds (PPG)-derived Pu into the studied area. Water column 239+240Pu inventory in the Bering Sea was lower than that reported for a comparable station in the Geochemical Ocean Sections Study, indicating that the Bering Sea inventory has been decreasing at the average rate of 2.6 Bq m-2 yr-1. The 240Pu/239Pu atom ratios ranged from 0.222 to 0.255 with a mean value of 0.235 in the northern North Pacific Ocean and from 0.215 to 0.237 with a mean value of 0.224 in the Bering Sea. The obtained 240Pu/239Pu ratios were clearly higher than the mean global fallout ratio of 0.18. These high atom ratios proved the presence of close-in fallout Pu from nuclear weapons testing at the PPG. The relative contribution of the global fallout and the PPG fallout were evaluated by using the two-end-member mixing model. The 239+240Pu inventories originating from the PPG fallout were calculated as 17.9-25.4 Bq m-2 in the northern North Pacific Ocean and 11.6-16.6 Bq m-2 in the Bering Sea, which corresponded to 38-54% and 31-45% of the total 239+240Pu inventory in the water column in the northern North Pacific Ocean and Bering Sea, respectively. A significant amount of the PPG-derived Pu has been transported to the northern North Pacific Ocean and Bering Sea. The proposed transport pathway accounting for the high 240Pu/239Pu ratio in the Bering Sea water column is the transportation of PPG-derived Pu by the North Equatorial Current followed by the Kuroshio Current, Kuroshio Extension, North Pacific Current and subsequently the Alaska Current, and then the Alaskan Stream.

Observation of Dispersion in the Japanese Coastal Area of Released 90Sr, 134Cs, and 137Cs from the Fukushima Daiichi Nuclear Power Plant to the Sea in 2013.

The March 2011 earthquake and tsunami resulted in significant damage to the Fukushima Daiichi Nuclear Power Plant (FDNPP) and the subsequent release of radionuclides into the ocean. Here, we investigated the spatial distribution of strontium-90 (90Sr) and cesium-134/cesium-137 (134, 137Cs) in surface seawater of the coastal region near the FDNPP. In the coastal region, 90Sr activity was high, from 0.89 to 29.13 mBq L-1, with detectable FDNPP site-derived 134Cs. This indicated that release of 90Sr from the power plant was ongoing even in May 2013, as was that of 134Cs and 137Cs. 90Sr activities measured at open ocean sites corresponded to background derived from atmospheric nuclear weapons testing fallout. The FDNPP site-derived 90Sr/137Cs activity ratios in seawater were much higher than those in the direct discharge event in March 2011, in river input, and in seabed sediment; those ratios showed large variability, ranging from 0.16 to 0.64 despite a short sampling period. This FDNPP site-derived 90Sr/137Cs activity ratio suggests that these radionuclides were mainly derived from stagnant water in the reactor and turbine buildings of the FDNPP, while a different source with a low 90Sr/137Cs ratio could contribute to and produce the temporal variability of the 90Sr/137Cs ratio in coastal water. We estimated the release rate of 90Sr from the power plant as 9.6 ± 6.1 GBq day-1 in May 2013 on the basis of the relationship between 90Sr and 137Cs activity (90Sr/137Cs = 0.66 ± 0.05) and 137Cs release rate.