A boy holds an amberjack caught near Fukushima prefecture in March 2011.… (EPA/Everett Kennedy Brown )
More than 18 months after a magnitude 9.0 earthquake, 40-foot tsunami and nuclear power plant woes that struck Japan starting March 11, 2011, levels of radioactive cesium 134 and cesium 137 originating from the crippled Fukushima-Daiichi plant remain elevated in some fish and seafood in nearby waters.
That suggests that radiation from the plant is still being released into the ocean, wrote Ken Buesseler, a marine of the Woods Hole Oceanographic Institution in Woods Hole, Mass., in a perspective article in Friday’s edition of the journal Nature (subscription required.)
Buesseler reviewed data on radionuclides in fish and other seafood that have been compiled by the Japanese Ministry of Agriculture, Forestry and Fisheries since March 23, 2011. Cesium levels were highest in bottom-dwelling fish caught near Fukushima prefecture, and lower in fish who live in the open ocean or closer to the surface, Buesseler reported.
He also noted that cesium levels had not declined, except “perhaps” in surface-dwelling fish. Over time, cesium that accumulates in the muscle tissue of fish should decline at a loss rate of a few percent per day. From this Buesseler reasoned that “there must be a continued source of cesium contamination associated with the seafloor.” One possibility could be radionuclides from Fukushima lurking in ocean bottom sediments.
The news was not all dire. The ”vast majority” of fish near Fukushima, Buesseler wrote, have radioactive cesium levels below the strict limits for seafood consumption adopted by the Japanese government in April 2012 to assuage consumer fears. And fish that migrate out of the area lose their cesium rapidly. As an example, Buesseler cited the example of bluefin tuna caught off the California coast, which carried minuscule-but-detectable amounts of radioactive cesium all the way across the Pacific.
But to fully understand how much radiation is in fish and seafood near the Fukushima Daiichi plant now and in the future, Buesseler added, studying the marine life caught in the area won’t be enough: Scientists will also need to learn more about where the cesium near the ocean floor is coming from and how it collects and accumulates.