Anthropogenic sources of radioactive pollution in oceans are many and can include the following:

Having discussed the issue of dumping nuclear waste in a previous blog post, this blog post will focus on radioactive pollution originating from nuclear accidents—such as the Fukushima Dai-ichi Nuclear Power Plant disaster—and how radioactive particles can be dispersed by ocean currents. This blog post will then conclude with a discussion on the impacts of these radioactive substances in oceans.

Apart from the atmospheric deposition of radioactive particles via nuclear fallout, the drainage of water from nuclear power plant (NPP) reactors following NPP-related disasters has also resulted in the contamination of neighbouring water bodies. Additionally, the rain-induced wash off has from the soil has also resulted in the introduction of radioactive substances into the sea (Prants et al., 2011). To better understand these processes, we will be examining the aftermath of the Fukushima Daiichi Nuclear Power Plant (FDNPP) and how the released radionuclides were dispersed.

The events of the Fukushima nuclear accident

The Fukushima nuclear accident occurred on 11 March 2011 following a 9.0-magnitude earthquake, coupled with a resultant tsunami event (Kim et al., 2013). Following this, the Fukushima Daiichi Nuclear Power Station lost external power supplies and AC power, which then resulted in reactors and spent fuel pods losing their cooling capabilities as well. This then led to explosions in three out of the six nuclear power units, along with serious damage towards the reactor core of another power unit (Hasegawa, 2012). The Fukushima nuclear disaster was rated 7 on the International Nuclear Event Scale, and has since been deemed as the first example of a “Quake and Nuke Disaster Complex”, as well as the first major accident of a NPP located on the coast (Hasegawa, 2012). Prants et al (2011) posit that the propagation of radioactive pollution from the NPP stems from two sources: the direct discharge of nuclear wastewater from the NPP, and deposition of radioactive substances as atmospheric precipitation into the ocean.

One of the most contentious issues regarding the aftermath of the Fukushima nuclear disaster is the release of around 10,400 cubic metres of contaminated wastewater into the Pacific Ocean in order to free up storage for wastewater with even higher contamination levels (World Nuclear Association, 2022). Additionally, despite receiving criticism for the initial release of contaminated wastewater, the Japanese government has announced plans in April 2021 to release huge quantities of contaminated nuclear wastewater into the Pacific Ocean from late 2022 to early 2023, over the next 30 years (Greenpeace, 2020, as cited in Yang et al., 2022). These actions were met with considerable opposition criticism from neighbouring countries (Norio et al., 2012), given the dispersal of radioactive substances via ocean currents as shown in the figure below:

Apart from contaminating oceans, the deposition of radionuclides on Japanese soils can also lead to a possibility of introducing contaminated sediments into rivers via runoff and erosion processes (Chartin et al., 2013). Alternatively, deposited radionuclides can also be deposited via soluble media—a process known as ‘liquid wash off’—into rivers and other water bodies (Pratama, 2015). Such occurrences can prove to be problematic, with coastal rivers becoming a constant supply of contaminated sediment to the Pacific Ocean (Chartin et al., 2013).

Apart from the volume of wastewater dumped, the contamination of the marine environment following the Fukushima nuclear disaster is also characterised by the location of the coastal waters of the FDNPP, which is located in the zone at where the Kuroshio and Oyashio currents interact (Bailly du Bois et al., 2011). These currents influence the extent of which the radioactive pollution is dispersed, with the Kuroshio current carrying the radioactive plume towards the centre of the Pacific Ocean (Jayne et al., 2009, as cited in Bailly du Bois et al., 2011). 

Impacts and concerns

One of the biggest concerns is the introduction of Caesium-137 and Caesium-134 into the marine environment, as these Cs isotopes are essentially soluble in seawater and can be transported over long distances by marine currents and dissipated throughout the ocean water masses (Sanchez-Cabeza et al., 2011, as cited in Bailly du Bois et al., 2011). Additionally, other radionuclides also tend to bind to suspended particles, resulting in sedimentary contamination as they deposit onto the seafloor (Evrard et al., 2011). As such, the nature of these radionuclides not only makes it more challenging to track and monitor the dispersal of radioactive substances in water bodies, but also that it is easier for these radioactive substances to affect marine life on a larger scale. The latter has been reflected in how 40% of fish species between April 2011 and April 2012 were found to have exceeded the Japanese radioactive regulatory limit of 100 Bq/kg-wet for radioactive Cs (Wada et al., 2013). In response to this, the Japanese government stopped the distribution of contaminated fishery products and contaminated feed for aquaculture (Morita et al., 2019).

A simulation conducted by Behrens et al., (2012, as cited in Koo et al., 2014) estimates that the dispersion and dilution of radioactive substances by ocean current activity would help to decrease peak radioactivity in the seawater off Fukushima gradually. However, while the ocean is able to dilute and disperse radioactive substances due to its large volume, the long half-life radionuclides, such as Caesium-137 and Caesium-134, are likely to still remain in the marine environment for prolonged periods (Yu et al., 2015). Both short- and long-lived radioactive elements can be absorbed by plankton and kelp, which can then accumulate in marine animals across the food chain (Grossman, 2011), ultimately affecting humans who consume them. 

References

Adhiraga Pratama, M., Yoneda, M., Shimada, Y., Matsui, Y., & Yamashiki, Y. (2015). Future projection of radiocesium flux to the ocean from the largest river impacted by Fukushima Daiichi Nuclear Power Plant. Scientific Reports, 5(1), 8408. https://doi.org/10.1038/srep08408

Bailly du Bois, P., Laguionie, P., Boust, D., Korsakissok, I., Didier, D., & Fiévet, B. (2012). Estimation of marine source-term following Fukushima Dai-ichi accident. Journal of Environmental Radioactivity, 114, 2–9. https://doi.org/10.1016/j.jenvrad.2011.11.015

Buesseler, K. O. (2012). Fishing for Answers off Fukushima. Science, 338(6106), 480–482. https://doi.org/10.1126/science.1228250

Chartin, C., Evrard, O., Onda, Y., Patin, J., Lefèvre, I., Ottlé, C., Ayrault, S., Lepage, H., & Bonté, P. (2013). Tracking the early dispersion of contaminated sediment along rivers draining the Fukushima radioactive pollution plume. Anthropocene, 1, 23–34. https://doi.org/10.1016/j.ancene.2013.07.001

Evrard, O., Laceby, J. P., Onda, Y., Wakiyama, Y., Jaegler, H., & Lefèvre, I. (2016). Quantifying the dilution of the radiocesium contamination in Fukushima coastal river sediment (2011–2015). Scientific Reports, 6(1), Article 1. https://doi.org/10.1038/srep34828

Fukushima Daiichi Accident—World Nuclear Association. (n.d.). Retrieved March 6, 2023, from https://world-nuclear.org/information-library/safety-and-security/safety-of-plants/fukushima-daiichi-accident.aspx

Grossman, E. (n.d.). Radioactivity in the Ocean: Diluted, But Far from Harmless. Yale E360. Retrieved March 6, 2023, from https://e360.yale.edu/features/radioactivity_in_the_ocean_diluted_but_far_from_harmless

Hasegawa, K. (2012). Facing Nuclear Risks: Lessons from the Fukushima Nuclear Disaster. International Journal of Japanese Sociology, 21(1), 84–91. https://doi.org/10.1111/j.1475-6781.2012.01164.x

Kim, Y., Kim, M., & Kim, W. (2013). Effect of the Fukushima nuclear disaster on global public acceptance of nuclear energy. Energy Policy, 61, 822–828. https://doi.org/10.1016/j.enpol.2013.06.107

Koo, Y.-H., Yang, Y.-S., & Song, K.-W. (2014). Radioactivity release from the Fukushima accident and its consequences: A review. Progress in Nuclear Energy, 74, 61–70. https://doi.org/10.1016/j.pnucene.2014.02.013

Lu, Y., Yuan, J., Du, D., Sun, B., & Yi, X. (2021). Monitoring long-term ecological impacts from release of Fukushima radiation water into ocean. Geography and Sustainability, 2(2), 95–98. https://doi.org/10.1016/j.geosus.2021.04.002

Morita, T., Ambe, D., Miki, S., Kaeriyama, H., & Shigenobu, Y. (2020). Impacts of the Fukushima Nuclear Accident on Fishery Products and Fishing Industry. In M. Fukumoto (Ed.), Low-Dose Radiation Effects on Animals and Ecosystems: Long-Term Study on the Fukushima Nuclear Accident (pp. 31–41). Springer. https://doi.org/10.1007/978-981-13-8218-5_3

Norio, O., Ye, T., Kajitani, Y., Shi, P., & Tatano, H. (2011). The 2011 eastern Japan great earthquake disaster: Overview and comments. International Journal of Disaster Risk Science, 2(1), 34–42. https://doi.org/10.1007/s13753-011-0004-9

Pickard, W. F. (2010). Finessing the fuel: Revisiting the challenge of radioactive waste disposal. Energy Policy, 38(2), 709–714. https://doi.org/10.1016/j.enpol.2009.11.022

Yablokov, A. V. (2005). Meta-Analysis of the Radioactive Pollution of the Ocean. In E. Levner, I. Linkov, & J.-M. Proth (Eds.), Strategic Management of Marine Ecosystems (pp. 11–27). Springer Netherlands. https://doi.org/10.1007/1-4020-3198-X_1

Yagi, N. (2019). The State of Fisheries and Marine Species in Fukushima: Six Years After the 2011 Disaster. In T. M. Nakanishi, M. O`Brien, & K. Tanoi (Eds.), Agricultural Implications of the Fukushima Nuclear Accident (III): After 7 Years (pp. 211–220). Springer. https://doi.org/10.1007/978-981-13-3218-0_18

Yang, B., Yin, K., Li, X., & Liu, Z. (2022). Graph model under grey and unknown preferences for resolving conflicts on discharging Fukushima nuclear wastewater into the ocean. Journal of Cleaner Production, 332, 130019. https://doi.org/10.1016/j.jclepro.2021.130019

Yu, W., He, J., Lin, W., Li, Y., Men, W., Wang, F., & Huang, J. (2015). Distribution and risk assessment of radionuclides released by Fukushima nuclear accident at the northwest Pacific. Journal of Environmental Radioactivity, 142, 54–61. https://doi.org/10.1016/j.jenvrad.2015.01.005