The detection of Fukushima-derived radiocesium in the Bering Sea and Arctic Ocean six years after the nuclear accident

Recent trends in the phytoremediation of radionuclide contamination of soil by cesium and strontium: Sources, mechanisms and methods: A comprehensive review

This comprehensive review examines recent trends in phytoremediation strategies to address soil radionuclide contamination by cesium (Cs) and strontium (Sr). Radionuclide contamination, resulting from natural processes and nuclear-related activities such as accidents and the operation of nuclear facilities, poses significant risks to the environment and human health. Cs and Sr, prominent radionuclides involved in nuclear accidents, exhibit chemical properties that contribute to their toxicity, including easy uptake, high solubility, and long half-lives. Phytoremediation is emerging as a promising and environmentally friendly approach to mitigate radionuclide contamination by exploiting the ability of plants to extract toxic elements from soil and water. This review focuses specifically on the removal of 90Sr and 137Cs, addressing their health risks and environmental implications. Understanding the mechanisms governing plant uptake of radionuclides is critical and is influenced by factors such as plant species, soil texture, and physicochemical properties. Phytoremediation not only addresses immediate contamination challenges but also provides long-term benefits for ecosystem restoration and sustainable development. By improving soil health, biodiversity, and ecosystem resilience, phytoremediation is in line with global sustainability goals and environmental protection initiatives. This review aims to provide insights into effective strategies for mitigating environmental hazards associated with radionuclide contamination and to highlight the importance of phytoremediation in environmental remediation efforts.

Continuous southwestward spread of Fukushima-derived 137Cs in the subtropical western North Pacific and its intrusion flux into the South China Sea

We provide transect profiles of 137Cs and 90Sr along 146.5°E, 136°E and 21°N in the subtropical western North Pacific (WNP) during May 2018. Exploiting the constant global fallout 137Cs/90Sr ratio, we separated Fukushima-derived 137Cs (137CsF) from background 137Cs. At most stations, 137CsF exhibited only one subsurface peak at 300 m depth, corresponding to subtropical mode water (STMW); however, at 25-28°N along 146.5°E and 25-26°N along 136°E, 137CsF exhibited two subsurface peaks, with another peak occurring at 500 m depth, corresponding to lighter central mode water (L-CMW). Temporal changes in 137CsF vertical profiles showed that 137CsF entrained by STMW has recirculated within the western subtropical gyre, while 137CsF entrained by L-CMW has turned southwestward and arrived the western basin in 2018. In the Luzon Strait, the entrance to the South China Sea (SCS), subsurface 137Cs increased since 2013 and peaked in approximately 2018. The estimated amount of 137CsF entering the SCS during 2013-2019 was 0.33 ± 0.10 PBq, equivalent to 1.7-2.2% of total leakage of 137CsF into the ocean. These results enhance our understanding of the protracted spread and fate of 137CsF in the subtropical WNP.

Surface and subsurface dispersal of radioactive materials from Fukushima by subpolar gyre and intermediate waters in the North Pacific

Radioactive materials were released into the ocean following the Fukushima Daiichi Nuclear Power Plant accident in 2011. Six years after the accident, the radioactive material concentration was markedly increased in the Okhotsk Intermediate Water (OIW) of the Sea of Okhotsk. This material may have been subjected to southward subsurface dispersal by the North Pacific Intermediate Water (NPIW), which originates from the OIW. The spatiotemporal limitations of available methods have made it challenging to track the dispersal paths of radioactive materials in the North Pacific Subpolar region. Here, we performed a tracer experiment using a three-dimensional numerical model to determine the path of 137Cs from Fukushima to the Sea of Okhotsk via surface subpolar gyre currents and subsurface dispersion by OIW and NPIW. The results showed that the 137Cs concentration in the Sea of Okhotsk increased via the surface current and moved progressively southward via OIW six years after the accident and eastward via OIW and NPIW nine years after the accident, indicating that 137Cs transported by NPIW entered the subtropical region. Based on experiments, this temporal change was mainly caused by ocean currents. Thus, subsurface recirculation of radioactive material via the OIW and NPIW should be considered based on the predicted path and travel time of additional materials released from the power plant.

Subarctic-scale transport of 134Cs to ocean surface off northeastern Japan in 2020

We studied the spatiotemporal variations in ¹³⁴Cs, ¹³⁷Cs, and ²²⁸Ra concentrations at the sea surface off southeastern Hokkaido, Japan (off-Doto region) from 2018 to 2022 using low-background γ-spectrometry. The ¹³⁴Cs concentrations in the off-Doto region, decay-corrected to the date of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, exhibited wide lateral variation each year (e.g., 0.7-1.1 mBq/L in 2020). By studying the ²²⁸Ra concentrations and salinity, this variation was explained based on the current mixing patterns. Furthermore, the ¹³⁴Cs concentrations in the waters highly affected by the Oyashio Current (OYC) gradually increased from 2018 to 2020, and subsequently decreased in 2022. This implies that the water mass maximally contaminated with ¹³⁴Cs was transported back to the side of the Japanese islands 10 years after the FDNPP accident along with counter-clockwise currents (e.g., the OYC) in the northern North Pacific Ocean. The ¹³⁴Cs concentrations in the OYC-affected waters in the off-Doto region in 2020 were ~ 1/6 times those in the ¹³⁴Cs-enriched core of waters off the western American Coast in 2015, which can be ascribed to dilution via spatial dispersion during subarctic current circulation. Overall, we elucidated the ocean-scale subarctic current systems in the northwestern North Pacific Ocean, including water circulation timespans.

Fukushima-derived radiocesium in the western subarctic area of the North Pacific Ocean, Bering Sea, and Arctic Ocean in 2019 and 2020

We measured dissolved radiocesium (¹³⁴Cs and ¹³⁷Cs) in surface seawater collected in the western subarctic area of the North Pacific Ocean, Bering Sea, and Arctic Ocean in 2019 and 2020. The radiocesium released from the accident of the Fukushima Dai-ichi nuclear power plant (FNPP1) in 2011 was still observed in these areas (∼2 Bq m^-3 decay-corrected to the date of the accident). In 2019/2020, the FNPP1-derived radiocesium concentrations in the Bering Sea and the Chukchi Sea, which is a marginal sea of the Arctic Ocean connecting the Bering Sea to the Arctic Ocean, were within the range of those observed in 2017/2018. On the other hand, the FNPP1-derived radiocesium was detected in the Arctic Ocean farther north of the Chukchi Sea in 2019/2020 for the first time. This was probably derived from the long-range transport of the FNPP1-derived radiocesium from the North Pacific coastal area of Japan to the Arctic Ocean through the Bering Sea during the past decade. The transport of the FNPP1-derived radiocesium from the Bering Sea to the western subarctic area in 2019/2020 is not clear, which implies the retainment of the FNPP1-derived radiocesium within the Bering Sea.

Zonal and vertical transports of Fukushima-derived radiocesium in the subarctic gyre of the North Pacific until 2014

The Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident in March 2011 resulted in serious radiocesium contamination of the North Pacific Ocean. Most of the radiocesium was dissolved in seawater and transported by surface currents and subduction of mode waters. Within several years after the accident, a high-concentration water plume of the FNPP1-derived radiocesium at the sea surface had been transported from Japan to the North American continent across the subarctic gyre of the North Pacific Ocean. We measured vertical profiles of dissolved radiocesium along the nominal 47°N zonal line across the North Pacific subarctic gyre twice, in summer 2012 and summer 2014. Using these data and published data, we quantitatively discussed the zonal and vertical transports of the water plume until 2014. The FNPP1-derived radiocesium remained in the surface layer shallower than 200 m, which is the approximate winter mixed-layer depth in the western subarctic gyre. The mean penetration depth did not change between 2012 and 2014. The highest concentration was observed at 180°W in 2012 and at 151°W in 2014, which suggests that the zonal transport speed of the water plume in the eastern subarctic gyre was about 3.8 cm s^-1. By combining the data from the zonal line in 2014 and a nominal 152°W meridional line in 2015, we elucidated the three-dimensional size of the high-concentration water plume in summer 2014. The total inventory of the FNPP1-derived radiocesium in the subarctic North Pacific Ocean, decay-corrected to the accident date, was estimated to be 12.0 ± 2.4 PBq.

Ambient temperature structures the gut microbiota of zebrafish to impact the response to radioactive pollution

Potential nuclear accidents propel serious environmental pollution, and the resultant radionuclide release devastates severely the environment severely and threatens aquatic organism survival. Likewise, ongoing climate change coupled with the gradual increase in global surface temperatures can also adversely impact the aquatic ecosystems. In the present study, we preconditioned zebrafish (Danio rerio) at three different temperatures (18 °C, 26 °C and 34 °C) to investigate the effects of a temperature profile on their radiosensitivity (exposure to 20 Gy of gamma rays) to identify the potential biochemical mechanism responsible for influencing radiosensitivity. We found that preconditioning of zebrafish at different temperatures moulded specific gut microbiota configurations and impacted hepatic glycometabolism and sensitivity to subsequent radiation. Following antibiotic treatment to reduce gut bacteria, these observed differences in the expression of hepatic glycometabolism-related genes and radiation-induced intestinal toxicity were minimal, supporting the hypothesis that the gut bacteria reshaped by different ambient temperatures might be the key modulators of hepatic functions and radiosensitivity in zebrafish. Together, our findings provide novel insights into the connection of radiation injuries with temperature alterations in fish, and suggest that maintaining the stability of gram-positive bacteria may be efficacious to protect aquatic organisms against short or long-term radioactive contamination in the context of global climate change.

An effective method for the determination of 106Ru in seawater by γ-spectrometry

¹⁰⁶Ru is a product originating from the fission reactions of uranium (²³⁵U) and plutonium (²³⁹Pu). ¹⁰⁶Ru represents a potential source of radioactive marine contamination since it makes up 70-90% of the total radioactivity of liquid effluents from fuel reprocessing plants; thus, it is important to effectively determine the quantity of ¹⁰⁶Ru in the natural environment. In this study, a simple and effective method was developed for the determination of ¹⁰⁶Ru in seawater by γ-spectrometry using NiS coprecipitation. In addition, the amounts of S^2- and Ni²⁺ added, Ru³⁺ carrier addition, pH, salinity, and sample volume were tested, and accordingly, optimal conditions were proposed. With the optimized conditions, the recovery of ¹⁰⁶Ru in seawater ranged from 85.3% to 92.3%, with an average of 88.1 ± 4.2%. The method proposed in the present study can also be applied to seawater samples with various salinities and volumes. For 20 L seawater and 24 h counting time on a γ-spectrometer, the limit of detection for ¹⁰⁶Ru in seawater was 5.74 mBq/L. In contrast to the traditional CoS method, the usage of NiS does not require any heating process; thus, the pretreatment time is substantially reduced. In addition, by using our method, ¹⁰⁶Ru can be determined in the presence of other radionuclides, further enhancing processing efficiency.

Marine Waste-Sources, Fate, Risks, Challenges and Research Needs

The article presents a comprehensive and cross-cutting review of key marine waste issues, taking into account: sources, fate, risks, transport pathways, threats, legislation, current challenges, and knowledge gaps. The growing amount of both human-created waste in seas and oceans and waste reaching marine ecosystems from land is one of today's challenges for the global economy and the European Union. It is predicted that if no decisive steps are taken to limit the amount of this type of waste, there may be more plastic waste than fish in the oceans after 2050. The influence of microplastics and nanoplastics on living organisms remains undiagnosed. Within the international and EU law, solutions are being developed to properly manage waste on board ships and to reduce the impact of processes related to the recycling of the vessels on the environment. Currently, over 80% of ships are dismantled in the countries of South Asia, in conditions that threaten the environment and the safety of workers. After World War 2, large quantities of chemical weapons were deposited in the seas. Steel containers with dangerous substances residing in the sea for over 70 years have begun leaking, thus polluting water. For many years, radioactive waste had also been dumped into marine ecosystems, although since 1993 there has been a total ban on such disposal of radionuclides. The impact of the COVID-19 pandemic on marine waste generation has also been presented as a significant factor influencing marine waste generation and management.

Synthesis of studies on significant atmospheric electrical effects of major nuclear accidents in Chernobyl and Fukushima

Radioactive materials released during the two most serious nuclear accidents in history, at Chernobyl and Fukushima, caused exceptionally significant contamination and perturbations of the environment. Among them, this paper focuses on the effects related to the atmospheric electricity (AE). Measurements of the most significant disturbances in the values of various AE parameters recorded near ground level are reviewed and the corresponding results are jointly evaluated. The Chernobyl and Fukushima events caused changes in the AE parameters both after long-distance transport (Chernobyl) and short-distance transport including re-suspension (Fukushima). The data indicates that the electrical conductivity of the air is more sensitive to the presence of airborne radioactivity than the atmospheric electric potential gradient (PG). PG, on the other hand, can be monitored more easily and its variation also reflects the vertical redistribution of radionuclides in the air due to their transport, deposition, and re-suspension from the ground. A brief overview of studies on atmospheric transport and deposition of radioactive clouds is given to facilitate the importance of considering the AE measurements in these subjects, and to incorporate those studies in interpreting the results of AE measurements. The AE measurements are particularly important in studying microphysical effects of enhanced radioactivity in the air where no other distance monitoring method exists, both for fair weather conditions wet conditions.