Abstract
Deep-ocean sediments, similarly to seawater, are important reservoirs of
137
Cs, an anthropogenic radionuclide with a relatively long half-live found in the Earth system. To better ...understand the geochemical behaviour of
137
Cs in the ocean, we examined the temporal changes of
137
Cs activity concentrations in the overlying waters and in sediments from the Far Eastern Seas (Sea of Japan, SOJ, and Okhotsk Sea, OS) during the period of 1998–2021. The
137
Cs activity levels showed exponential changes during the observed period. The decay-corrected change rates of
137
Cs in deep waters of SOJ exhibited a slow increase, while
137
Cs levels in seawater and sediment in OS decreased gradually. This reflects a topographical difference, as SOJ is a semi-closed sea, whereas OS receives continuously inflow of subarctic waters. It was confirmed that
137
Cs released after the Fukushima Dai-ichi Nuclear Power Plant accident was rapidly transported into the deep waters of the SOJ. To elucidate the transfer processes of
137
Cs from seawater to sediment, we discussed the temporal changes of the partition coefficients (K
d
) of
137
Cs between the overlying water and the surface sediment. In shallow areas (< 1500 m water depth), K
d
values were almost constant within the sampling periods, although the temporal changes in the K
d
values occurred in deeper waters (> 2500 m depth). The K
d
values increased with increasing depth, which may reflect a pressure effect as a possible mechanism. These findings suggest that chemical processes may be important factors controlling the transport of
137
Cs between seawater and sediment, although more complicated phenomena occurred in deep waters and sediments of the SOJ (> 3000 m depth).
The impact of the Fukushima-derived radiostrontium (90Sr and 89Sr) on the western North Pacific Ocean has not been well established, although 90Sr concentrations recorded in surface seawater offshore ...of the damaged Fukushima Dai-ichi nuclear power plant were in some areas comparable to or even higher than (as those in December 2011 with 400 kBq m–3 90Sr) the 137Cs levels. The total amount of 90Sr released to the marine environment in the form of highly radioactive wastewater could reach about 1 PBq. Long-term series (1960–2010) of 90Sr concentration measurements in subtropical surface waters of the western North Pacific indicated that its concentration has been decreasing gradually with a half-life of 14 y. The pre-Fukushima 90Sr levels in surface waters, including coastal waters near Fukushima, were estimated to be 1 Bq m–3. To better assess the impact of about 4–5 orders of magnitude increased radiostrontium levels on the marine environment, more detail measurements in seawater and biota of the western North Pacific are required.
The investigation of the impact of the Fukushima accident is still going on although more than ten years have passed since the disaster. The main goal of this paper was to summarize the results of ...tritium and radiocarbon determinations in different environmental samples, possibly connected with the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. A document containing compiled data may serve as a solid basis for further research in the selected fields. To accomplish such effort, we went through dozens of relevant published papers, reporting 3H and 14C activity concentrations in precipitations, groundwater, seawater, river systems, tree rings, and, in some more extraordinary samples, such as herbaceous plants or debris from the damaged reactor buildings. As the referenced results would not be obtainable without adequate analytical techniques, the most common methods for routine measurement of tritium and radiocarbon concentrations are discussed as well. We believe that the correct identification of the affected environmental compartments could help quantify the released 3H and 14C activities and track their following fate, which could be especially important for plans to discharge contaminated water from the FDNPP in the upcoming years.
Plutonium isotopes have primarily been injected to the stratosphere by the atmospheric nuclear weapon tests and the burn-up of the SNAP-9A satellite. Here we show by using published data that the ...stratospheric plutonium exponentially decreased with apparent residence time of 1.5 ± 0.5 years, and that the temporal variations of plutonium in surface air followed the stratospheric trends until the early 1980s. In the 2000s, plutonium and its isotope ratios in the atmosphere varied dynamically, and sporadic high concentrations of (239,240)Pu reported for the lower stratospheric and upper tropospheric aerosols may be due to environmental events such as the global dust outbreaks and biomass burning.
Variations of Fukushima-derived radionuclides ((90)Sr, (134)Cs and (137)Cs) in seawater and biota offshore Fukushima and in the NW Pacific Ocean were investigated and radiation doses to the Japanese ...and world population from ingestion of seafood contaminated by Fukushima radionuclides were estimated and compared with those from other sources of anthropogenic and natural radionuclides. The total effective dose commitment from ingestion of radionuclides in fish, shellfish and seaweed caught in coastal waters off Fukushima was estimated to be 0.6 ± 0.4 mSv/y. The individual effective dose commitment from consumption of radioactive-contaminated fish caught in the open Pacific Ocean was estimated to be 0.07 ± 0.05 mSv/y. These doses are comparable or much lower than doses delivered from the consumption of natural (210)Po in fish and in shellfish (0.7 mSv/y). The estimated individual doses have been below the levels when any health damage of the Japanese and world population could be expected.
Investigation of neutron-induced background was carried out by studying interactions of cosmic-ray neutrons with an HPGe detector inside its shield placed on a ground floor of a 3-storey building. ...The study was conducted experimentally and by Monte Carlo simulations using GEANT4 simulation tool. Detailed analysis of measured background γ-ray spectra showed that many γ-lines visible in the spectra were induced by neutrons. The majority of detected γ-rays originated in germanium, copper, lead and tin. Iron and aluminium components were less important background sources. Inelastic scattering and neutron capture were the most often occurring processes of neutron interactions with the detector and its shielding. The contamination by natural radionuclides, specifically of 40K, 214Pb, 214Bi and 208Tl, was also present in the background spectra. Nevertheless, approximately 35% of 208Tl peak at the energy of 2614.51 keV was produced by inelastic scattering of neutrons on 208Pb nuclei. The experimental background was compared with GEANT4 simulations, which were carried out without and with the shielding layer of the building. The final integral counting rates for measured spectrum in the energy range from 50 keV to 2875 keV was 1.26 ± 0.07 s−1 and for simulated one 1.25 ± 0.13 s−1, indicating a good agreement with the experiment.
•Study of cosmic ray interactions with an HPGe detector was carried out.•Many γ-lines visible in the spectra were induced by neutrons.•Inelastic scattering and neutron capture were the most often occurring processes.•GEANT4 simulations were in a very satisfactory agreement with the experiment.•Inelastic neutron scattering on 208Pb nuclei contributes by 35% to the 2614.51 keV peak.
90Sr and 137Cs activity concentrations in surface waters of the Sea of Japan (SOJ) decreased during the period of 1993–2010 with effective half-lives of 18 and 15 y, respectively. The longer ...effective half-life of 90Sr in the SOJ may suggest a surplus of 90Sr to SOJ surface waters, however, no clear evidence of possible 90Sr source has been found. After the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, temporal variations of 137Cs in the surface water of the SOJ have changed, while 90Sr variations followed the pre-accident trends. The 90Sr/137Cs ratios reveal that increases of 137Cs due to the FDNPP accident continued in surface waters of the SOJ until 2016.
•137Cs and 90Sr are useful tracers for studying processes in the Sea of Japan (SOJ).•Effective half-life of 90Sr in surface water of the SOJ is longer than expected.•90Sr/137Cs activity ratios help to elucidate oceanic effects of the Fukushima accident.
Results of radiocarbon (14C) analysis of a tree-ring series from Bratislava, Slovakia, covering the period from 1970 to 2004 are presented. For a part of this time period, monthly 14C measurements of ...atmospheric carbon dioxide from Bratislava sampling station are compared with the tree-ring results. The effects of fossil CO2 emissions on 14C levels in the environment are emphasized by comparison with atmospheric clean air reference values (Schauinsland, Germany). The presented results from Bratislava are also set against the previously measured tree-ring series from Low Tatras mountain region in Slovakia, representing regional clean air radiocarbon levels in the biosphere. The observed 14C levels of Bratislava tree rings and atmospheric CO2 in 1970s and 1980s are significantly lower than clean air data, indicating severe fossil CO2 pollution in Bratislava during this time period.
Tritium, radiocarbon and radiocesium concentrations in water column samples in coastal waters offshore Fukushima and in the western North Pacific Ocean collected in 2011–2012 during the ...Ka'imikai-o-Kanaloa (KoK) cruise are compared with other published results. The highest levels in surface seawater were observed for 134Cs and 137Cs in seawater samples collected offshore Fukushima (up to 1.1 Bq L−1), which represent an increase by about three orders of magnitude when compared with the pre-Fukushima concentration. Tritium levels were much lower (up to 0.15 Bq L−1), representing an increase by about a factor of 6. The impact on the radiocarbon distribution was measurable, but the observed levels were only by about 9% above the global fallout background. The 137Cs (and similarly 134Cs) inventory in the water column of the investigated western North Pacific region was (2.7 ± 0.4) PBq, while for 3H it was only (0.3 ± 0.2) PBq. Direct releases of highly contaminated water from the damaged Fukushima NPP, as well as dry and wet depositions of these radionuclides over the western North Pacific considerably changed their distribution patterns in seawater. Presently we can distinguish Fukushima labeled waters from global fallout background thanks to short-lived 134Cs. However, in the long-term perspective when 134Cs will decay, new distribution patterns of 3H, 14C and 137Cs in the Pacific Ocean should be established for future oceanographic and climate change studies in the Pacific Ocean.
•Radiocesium, tritium and radiocarbon showed elevated levels in seawater of the western North Pacific.•The water column inventories of 137Cs and 3H were 2.7 ± 0.4 and 0.3 ± 0.2 PBq, respectively.•The radiocarbon levels were by about 9% above the global fallout background.•Released radionuclides will be useful in future oceanographic and climate studies.
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