The Fukushima nuclear disaster delivered massive amounts of radioactivity into the sea, and radioactive isotopes soon made their way into the marine food chain.
- Radioisotopes released into the atmosphere from the Daiichi nuclear power plant fell into the ocean
- Water used to cool reactors flushed radioisotopes fell into the sea
- Microscopic marine plants (phytoplankton) take up radioisotopes from seawater around them – this is the beginning of the bioaccumulation of radiation into the marine food chain
- Contaminants move up the food chain from tiny marine animals (zooplankton), fish larvae, fish and larger predators
- Some contaminants end up in fecal pellets and other detrital particles that settle to the seafloor and accumulate as sediments
- Some radioisotopes in sediments may be remobilised into overlying waters and absorbed by bottom-dwelling organisms
Researchers claim that given the scale of the Pacific ocean – the world’s vastest body of water – radioactivity in the sea at Fukushima will be flushed out and diluted to low levels. However, the bioaccumulation of longer half-life radioactive elements by fish will have far-reaching effects.
Once taken up by marine creatures, biomagnification of radioactive substances may occur because radioactive materials are likely to be long-lived, mobile and biologically active.
Iodine-131 can be easily taken up by fish by their thyroid tissue, and also readily absorbed by seaweed and kelp. The likelihood of bioaccumulation is high, but its half-life of 8 days reduces its risk of biomagnification up the food chain. In turn, Caesium-137 being mobile (highly soluble in water) and long-lived (half-life: 30y) means that it is likely to accumulate in organisms up the marine food chain, and ultimately to humans where we consume these marine creatures for food. Caesium-137 can also be taken up by cells throughout the body, and distributed in soft tissues especially muscle tissue, increasing cancer risk.
The biomagnification of radioactive caesium has been documented: A 1999 study found that seals and porpoises in the Irish Sea had concentrations by a factor of 300 relative to that of in seawater, and a factor of 3 to 4 compared to the fish they ate.
In the case of the Fukushima disaster, seawater contamination was largely caused by atmospheric deposition. Iodine-131 was detected in seawater at levels 1850 times the statutory limit two weeks after the accident, and Caesium-137 at levels 80 times the limit. 2 months after the accident, 10 of the 22 seaweed samples collected near the nuclear plant showed concentrations of iodine-131 at 5 times the Japanese standard for food. This is despite the fact that iodine-131 is known to have a half-life of just 8 days.
- After the accident, United States’ FDA issued an import alert for food products from four Japanese prefectures
- About a year after the accident, commercial fishing in the region surrounding Fukushima was limited to octopus and whelk (a type of sea snail) because these species are thought to be less likely to accumulate radioactive substances in their bodies
- South Korea banned all fish imports from a large area of Japan, due to fears over the safety of seafood
- China also maintained a ban on dairy, vegetable and seafood imports from several prefectures since March 2011
Some thoughts of mine
Understanding bioaccumulation and biomagnification in marine biota is especially important in the case of Japan, where they have high seafood consumption rates. The seafood industry is also a vital one for many fishermen. Perhaps in the case of Singapore, radiation pollution is probably of little concern, as opposed to air pollution which has received much attention. Perhaps it is also why we need to understand more about these issues, in order to truly understand the severity of environmental pollution on a broader level.
One interesting point I noted while doing research was regarding the contamination of bluefin tuna in the Pacific Ocean. Some sources claim that it is safe to eat, while others claim that they are highly contaminated. The production of “scientific” knowledge is highly contestable and this has an impact of how people may perceive or respond to pollution risks. Despite causing much doubt, people were likely to err on the side of caution. Some fishermen have reflected that even if the catch are deemed safe for consumption, no one would buy them. From my point of view, even if I were told that seafood from Japan had radiation levels below the limits, it is unlikely that I would consume them. Given the haunting images of cancer-stricken and mutagenic victims of radiation contamination (especially from the Chernobyl accident), the stigma towards radiation pollution is likely the persist.
Thanks for reading!
Grossman, E. (2011, April 7). Radioactivity in the Ocean: Diluted, But Far from Harmless. Retrieved March 2015, from Environment 360: http://e360.yale.edu/feature/radioactivity_in_the_ocean_diluted_but_far_from_harmless/2391/
Mader, S. S. (1996). Biology. W.M.C. Brown Publishers.
McCurry, J. (2013, August 9). Toxic Fukushima fallout threatens fishermen’s livelihoods. Retrieved March 2015, from The Guardian: http://www.theguardian.com/world/2013/aug/09/fukushima-fallout-threatens-fishermens-livelihoods
McCurry, J. (2013, Setember 6). South Korea bans fish imports from Japan’s Fukushima region. Retrieved March 2015, from The Guardian: http://www.theguardian.com/world/2013/sep/06/south-korea-fish-japan-fukushima
Pacchioli, D. (2013, May 2). How Is Fukushima’s Fallout Affecting Marine Life? Retrieved March 2015, from Woods Hole Oceanographic Institution: http://www.whoi.edu/oceanus/feature/how-is-fukushimas-fallout-affecting-marine-life
Tabuchi, H. (2012, June 25). Fears Accompany Fishermen in Japanese Disaster Region. Retrieved March 2015, from The New York Times: http://www.nytimes.com/2012/06/26/world/asia/fears-accompany-fishermen-in-japanese-disaster-region.html?_r=0