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1.
Mar Pollut Bull ; 197: 115663, 2023 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-37897967

RESUMO

Radioactive cesium (137Cs) is distributed in the world's oceans as a result of global fallout from atmospheric nuclear weapons tests, releases from fuel reprocessing plants, and inputs from nuclear power plant accident. In order to detect future radionuclide contamination, it is necessary to establish a baseline global distribution of radionuclides such as 137Cs and to understand the ocean transport processes that lead to that distribution. In order to aid in the interpretation of the observed database, we have conducted a suite of simulations of the distribution of 137Cs using a global ocean general circulation model (OGCM). Simulated 137Cs radioactivity concentrations agree well with observations, and the results were used to estimate the changes in inventories for each ocean basin. 137Cs activity concentration from atmospheric nuclear weapons tests are expected to be detectable in the world ocean until at least 2030.


Assuntos
Acidente Nuclear de Fukushima , Monitoramento de Radiação , Poluentes Radioativos da Água , Poluentes Radioativos da Água/análise , Oceanos e Mares , Radioisótopos de Césio/análise , Japão , Oceano Pacífico
2.
J Environ Radioact ; 214-215: 106173, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32063291

RESUMO

A series of accidents at the Fukushima Dai-ichi Nuclear Power Plant (1F NPP) following the Great East Japan Earthquake and tsunami of 11 March 2011 resulted in the release of radioactive materials to the ocean. We used the Regional Ocean Model System (ROMS) to simulate the 137Cs activity in the oceanic area off Fukushima, with the sources of radioactivity being direct release, atmospheric deposition, river discharge, and inflow across the domain boundary. The direct release rate of 137Cs after the accident until the end of 2016 was estimated by comparing simulated results with measured 137Cs activities adjacent to the 1F NPP. River discharge rates of 137Cs were estimated by multiplying simulated river flow rates by the dissolved 137Cs activities, which were estimated by an empirical function. Inflow of 137Cs across the domain boundary was set according to the results of a North Pacific Ocean model. Because the spatiotemporal variability of 137Cs activity was large, the simulated results were compared with the annual averaged observed 137Cs activity distribution. Normalized annual averaged 137Cs activity distributions in the regional ocean were similar for each year from 2013 to 2016. This result suggests that the annual averaged distribution is predictable. Simulated 137Cs activity attributable to direct release was in good agreement with measurement data from the coastal zone adjacent to the 1F NPP. Comparison of the simulated results with measured activity in the offshore area indicated that the simulation slightly underestimated the activity attributable to inflow across the domain boundary. This result suggests that recirculation of subducted 137Cs to the surface layer was underestimated by the North Pacific model. During the study period, the effect of river discharge on oceanic 137Cs activity was small compared to the effect of directly released 137Cs.


Assuntos
Acidente Nuclear de Fukushima , Monitoramento de Radiação , Radioisótopos de Césio , Japão , Centrais Nucleares , Oceano Pacífico , Rios , Poluentes Radioativos da Água
3.
J Environ Radioact ; 189: 93-102, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-29626724

RESUMO

We report temporal variations of 137Cs activity concentrations in surface waters of six regions of the western and central North Pacific Ocean during 2011-2017 using a combination of 1264 previously published data and 42 new data. In the western and central North Pacific Ocean at latitudes of 30-42°N and longitudes of 140°E to 160°W, eastward transport of radiocaesium was clearly apparent. 137Cs activity concentrations in surface water decreased rapidly to ∼2-3 Bq m-3 in 2015/2016, still a bit higher than 137Cs activity concentrations before the FNPP1 accident (1.5-2 Bq m-3). 134Cs/137Cs activity ratios decay-corrected to 11 March 2011 were ∼0.5-0.8. To the south of 30°N and between 130°E and 160°W in the western and central Pacific Ocean, 137Cs activity concentrations were around 1-7 Bq m-3 in 2011/2012 but then stabilized at a few Bq m-3 up to 2017.134Cs activity concentrations were detected at levels of 0.1-0.9 Bq m-3, and 134Cs/137Cs activity ratios decay-corrected to 11 March 2011 were ∼0.3-0.5. Temporal variations of model-simulated 137Cs activity concentrations in surface water in the region of interest showed good agreement with observations, except in the southwestern North Pacific Ocean.


Assuntos
Radioisótopos de Césio/análise , Acidente Nuclear de Fukushima , Monitoramento de Radiação , Água do Mar/química , Poluentes Radioativos da Água/análise , Japão , Oceano Pacífico , Fatores de Tempo , Movimentos da Água
4.
J Environ Radioact ; 151 Pt 2: 495-501, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-26070950

RESUMO

Radiocesium ((134)Cs and (137)Cs) released into the Fukushima coastal environment was transferred to marine biota inhabiting the Pacific Ocean coastal waters of eastern Japan. Though the levels in most of the edible marine species decreased overtime, radiocesium concentrations in some fishes were still remained higher than the Japanese regulatory limit for seafood products. In this study, a dynamic food chain transfer model was applied to reconstruct (137)Cs levels in olive flounder by adopting the radiocesium concentrations in small demersal fish which constitute an important fraction of the diet of the olive flounder particularly inhabiting area near Fukushima. In addition, (137)Cs levels in slime flounder were also simulated using reported radiocesium concentrations in some prey organisms. The simulated results from Onahama on the southern border of the Fukushima coastline, and at Choshi the southernmost point where the contaminated water mass was transported by the Oyashio current, were assessed in order to identify what can be explained from present information, and what remains to be clarified three years after the Fukushima Dai-ichi nuclear power plant (1FNPP) accident. As a result, the observed (137)Cs concentrations in planktivorous fish and their predator fish could be explained by the theoretically-derived simulated levels. On the other hand, the slow (137)Cs depuration in slime flounder can be attributed to uptake from unknown sources for which the uptake fluxes were of a similar magnitude as the excretion fluxes. Since the reported (137)Cs concentrations in benthic invertebrates off Onahama were higher than the simulated values, radiocesium transfer from these benthic detritivorous invertebrates to slime flounder via ingestion was suggested as a cause for the observed slow depuration of (137)Cs in demersal fish off southern Fukushima. Furthermore, the slower depuration in the demersal fish likely required an additional source of (137)Cs, i.e. contaminated detritus or sediment which was entrained with the prey during the active sediment feeding of this fish species.


Assuntos
Organismos Aquáticos/metabolismo , Radioisótopos de Césio/metabolismo , Cadeia Alimentar , Modelos Biológicos , Poluentes Radioativos da Água/metabolismo , Simulação por Computador , Acidente Nuclear de Fukushima , Japão , Oceano Pacífico , Monitoramento de Radiação
5.
J Environ Radioact ; 147: 130-41, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26065930

RESUMO

Radiocesium ((134)Cs and (137)Cs) originating from the Fukushima Dai-ichi Nuclear Power Plant (1FNPP) has contaminated coastal waters and been subsequently transferred to the marine biota along the Pacific coastal region of eastern Japan. To clarify the mechanism of radiocesium biokinetics in olive flounder, a commercially valuable and piscivorous predator, the biokinetics of (137)Cs was simulated using a dynamic biological compartment model and then validated with the measured concentrations in available monitoring data. The (137)Cs concentrations in seawater of the Pacific coastal sites of eastern Japan, from Kesen-numa (170 km north from the 1FNPP) to Choshi (190 km south from the 1FNPP), were reconstructed by fitting the simulated levels to the observed concentrations. Simulated values were verified by measured radiocesium levels in sedentary organism such as macro-algae and mussels inhabiting each study site which had accumulated radiocesium in their ambient environment from the beginning of the accident. Using reconstructed (137)Cs concentrations in seawater, the (137)Cs levels in olive flounder and its main planktivorous prey fish, e.g. anchovy, sand lance, whitebait, etc., were simulated and compared with observed concentrations to clarify the biokinetics of radiocesium in these organisms. This assessment showed that the determining factor for the maximum radiocesium concentrations in fish in the plankton food chain is likely to be the initial radiocesium concentration which they were exposed to during the contamination stage. Furthermore, the simulated (137)Cs concentrations in gut contents of olive flounder were verified by measured (137)Cs concentrations in the stomach contents of this fish collected within 30 km from the 1FNPP. These results indicated that the decrease of (137)Cs levels in their prey organisms was the primary determining factor of radiocesium depuration, and the resultant ecological half-lives were 140-160 d in the olive flounder, by the simulation.


Assuntos
Bivalves/metabolismo , Radioisótopos de Césio/metabolismo , Peixes/metabolismo , Alga Marinha/metabolismo , Poluentes Radioativos da Água/metabolismo , Animais , Radioisótopos de Césio/análise , Linguados/metabolismo , Cadeia Alimentar , Acidente Nuclear de Fukushima , Conteúdo Gastrointestinal/química , Japão , Cinética , Modelos Teóricos , Monitoramento de Radiação , Água do Mar/análise , Poluentes Radioativos da Água/análise
6.
J Environ Radioact ; 136: 218-28, 2014 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-24980438

RESUMO

We used numerical simulations to investigate major controls on spatiotemporal variations of (137)Cs activities in seabed sediments off the Fukushima coast during the first year after the Fukushima Daiichi Nuclear Power Plant accident. The numerical model we used includes (137)Cs transfer between bottom water and sediment by adsorption and desorption, and radioactive decay. The model successfully reproduced major features of the observed spatiotemporal variations of (137)Cs activities in sediments. The spatial pattern of (137)Cs in sediments, which mainly reflected the history of (137)Cs activities in bottom water overlying the sediments and the sediment particle size distribution, became established during the first several months after the accident. The simulated temporal persistence of the (137)Cs activity in the sediments was due to adsorption of (137)Cs onto the sediment mineral fraction having a long desorption timescale of (137)Cs. The simulated total (137)Cs inventory in sediments integrated over the offshore area, where most of the monitoring stations were located, was on the order of 10(13) Bq; this value is consistent with a previous estimate based on observed data. Taking into account (137)Cs activities in sediments in both the coastal area and in the vicinity of the power plant, the simulated total inventory of (137)Cs in sediments off the Fukushima coast increased to a value on the order of 10(14) Bq.


Assuntos
Acidente Nuclear de Fukushima , Sedimentos Geológicos/análise , Poluentes Radioativos da Água/análise , Radioisótopos de Césio/análise , Japão , Modelos Teóricos , Oceano Pacífico
7.
J Environ Radioact ; 124: 1-12, 2013 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-23639689

RESUMO

The Fukushima Dai-ichi Nuclear Power Plant (1F NPP) accident occurred on 11 March 2011. The accident introduced (137)Cs into the coastal waters which was subsequently transferred to the local coastal biota thereby elevating the concentration of this radionuclide in coastal organisms. In this study, the radioactive cesium levels in coastal biota from the southern Fukushima area were simulated using a dynamic biological compartment model. The simulation derived the possible maximum radioactive cesium levels in organisms, indicating that the maximum (137)Cs concentrations in invertebrates, benthic fish and predator fish occurred during late April, late May and late July, respectively in the studied area where the source was mainly the direct leakage of (137)Cs effluent from the 1F NPP. The delay of a (137)Cs increase in fish was explained by the gradual food chain transfer of (137)Cs introduced to the ecosystem from the initial contamination of the seawater. The model also provided the degree of radionuclide depuration in organisms, and it demonstrated the latest start of the decontamination phase in benthic fish. The ecological half-lives, derived both from model simulation and observation, were 1-4 months in invertebrates, and 2-9 months in plankton feeding fish and coastal predator fish from the studied area. In contrast, it was not possible to similarly calculate these parameters in benthic fish because of an unidentified additional radionuclide source which was deduced from the biological compartment model. To adequately reconstruct the in-situ depuration of radiocesium in benthic fish in the natural ecosystem, a contamination source associated with the bottom sediments is necessary.


Assuntos
Radioisótopos de Césio/metabolismo , Cadeia Alimentar , Acidente Nuclear de Fukushima , Modelos Teóricos , Poluentes Radioativos da Água/metabolismo , Animais , Biota , Radioisótopos de Césio/análise , Peixes/metabolismo , Invertebrados/metabolismo , Japão , Plantas/metabolismo , Monitoramento de Radiação , Água do Mar , Poluentes Radioativos da Água/análise
8.
J Environ Radioact ; 111: 100-8, 2012 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-22071362

RESUMO

Radioactive materials were released to the environment from the Fukushima Dai-ichi Nuclear Power Plant as a result of the reactor accident after the Tohoku earthquake and tsunami of 11 March 2011. The measured (137)Cs concentration in a seawater sample near the Fukushima Dai-ichi Nuclear Power Plant site reached 68 kBq L(-1) (6.8 × 10(4)Bq L(-1)) on 6 April. The two major likely pathways from the accident site to the ocean existed: direct release of high radioactive liquid wastes to the ocean and the deposition of airborne radioactivity to the ocean surface. By analysis of the (131)I/(137)Cs activity ratio, we determined that direct release from the site contributed more to the measured (137)Cs concentration than atmospheric deposition did. We then used a regional ocean model to simulate the (137)Cs concentrations resulting from the direct release to the ocean off Fukushima and found that from March 26 to the end of May the total amount of (137)Cs directly released was 3.5 ± 0.7 PBq ((3.5 ± 0.7) × 10(15)Bq). The simulated temporal change in (137)Cs concentrations near the Fukushima Daini Nuclear Power Plant site agreed well with observations. Our simulation results showed that (1) the released (137)Cs advected southward along the coast during the simulation period; (2) the eastward-flowing Kuroshio and its extension transported (137)C during May 2011; and (3) (137)Cs concentrations decreased to less than 10 BqL(-1) by the end of May 2011 in the whole simulation domain as a result of oceanic advection and diffusion. We compared the total amount and concentration of (137)Cs released from the Fukushima Dai-ichi reactors to the ocean with the (137)Cs released to the ocean by global fallout. Even though the measured (137)Cs concentration from the Fukushima accident was the highest recorded, the total released amount of (137)Cs was not very large. Therefore, the effect of (137)Cs released from the Fukushima Dai-ichi reactors on concentration in the whole North Pacific was smaller than that of past release events such as global fallout, and the amount of (137)Cs expected to reach other oceanic basins is negligible comparing with the past radioactive input.


Assuntos
Desastres , Terremotos , Modelos Teóricos , Monitoramento de Radiação/estatística & dados numéricos , Cinza Radioativa/análise , Liberação Nociva de Radioativos/história , Tsunamis , Poluentes Radioativos da Água/análise , Radioisótopos de Césio/análise , Simulação por Computador , Geografia , História do Século XXI , Radioisótopos do Iodo/análise , Japão , Oceanos e Mares , Liberação Nociva de Radioativos/estatística & dados numéricos , Fatores de Tempo , Movimentos da Água
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