Don't expect to see Fukushima flounder on the menu anytime soon. Bottom-dwelling fish living near the coast of Fukushima prefecture are still contaminated with radioactive isotopes, according to a new analysis just published in the journal Science. The study suggests that the sea floor near Fukushima may be contaminated for decades to come.
More than 19 months have passed since the Fukushima Dai-ichi nuclear power station lost power following a devastating offshore earthquake and tsunami, causing partial meltdowns in three of its reactors and a large release of radioactive materials into the air. Winds blew some of those radioactive materials out to sea, and rain carried them down into the ocean water. In addition, water used to cool the damaged reactors flowed from the coastal power plant into the ocean. In the weeks and months after the accident, plant owner TEPCO struggled to stop leaks of contaminated water into the sea and to create a closed loop for the cooling water.
Ken Buesseler of Woods Hole Oceanographic Institution had previously studied radiation levels in the ocean waters near Fukushima, and has now turned his attention to fish. Buesseler analyzed data from Japan's fisheries agency, which has been testing fish and other sea life for radioactive isotopes since the accident. When Buesseler examined the data for fish off the coast of Fukushima, he found that 40 percent of bottom-dwelling fish (including flounder, skate, cod, halibut, and sole) had radiation levels that exceed the current safety standards in Japan. Surface-dwelling and open ocean fish didn't exceed those limits.
Buesseler told me that the most striking finding is that the radiation levels in these fish aren't going down. "I was struck by how they really haven’t changed over the last year," he said. He was looking specifically at the radioactive isotopes cesium-134 and cesium-137, both of which were released in the Fukushima Dai-ichi accident. "Since cesium doesn’t bioaccumulate to a significant degree, and in fact is lost when fish move to a less contaminated area, this implies that the cesium source is still there," he said. The bottom-dwelling fish are probably constantly re-contaminated by radioactive sediments layered on the seafloor, says Buesseler. And it may take decades for those sediments to be dispersed, and for the fishing area to be considered safe again.
It's also very possible that the Fukushima Dai-ichi power station is still leaking radioactive water, says Buesseler. "It could be that they’re not recovering all that cooling water, there could be leaks in the basement," he says. "Even if they’re not putting new water out, the groundwater is still contaminated."
TEPCO spokesman Yoshikazu Nagai says that the company has taken numerous actions to prevent further contamination of the ocean near the power plant. "We have covered the marine soil to prevent radioactive materials from being diffused into the ocean area near the power station and are currently in the process of building a water shielding wall to prevent groundwater flowing out of the power station site," he wrote in an email. That "water shielding wall" is a sunken barrier positioned between the reactor buildings and the coast.
Nagai wrote that TEPCO's ongoing monitoring of the ocean shows no increase in radiation levels. He did not directly respond when I asked whether TEPCO has information about leaks of contaminated water from the power station.
Image: Ken Buesseler
Eliza Strickland is a senior editor at IEEE Spectrum, where she covers AI, biomedical engineering, and other topics. She holds a master’s degree in journalism from Columbia University.