A fish containing levels of radioactive cesium, 180 times more than the Japanese safety limit, was found living near drainage outlets at the Fukushima Daiichi nuclear plant in May. 

The black rockfish was caught on May 18 by plant operator Tokyo Electric Power Company (Tepco) with 18,000 becquerels in every kg of cesium-137, compared to the legal maximum level of 100 becquerels per kg. 

Japan has plans to release 1.3m tonnes of treated water from the Fukushima plant, sparking concern in the area, despite the UN International Atomic Energy Agency (IAEA)'s approval. That said, Hong Kong threatened to ban food imports from ten Japanese prefectures if all goes as planned.

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Japanese seafood imports are being tested for radioactivity in China, which has led some wholesalers to halt importing such Japanese produce. 

Regarding the water discharge, the Tepco official expressed confidence that there will be minimal impact on the public and the environment. 

How was the water originally contaminated? 

During the March 2011 disaster, rainwater from the areas around reactors one, two, and three, which melted down in the disaster, and water flowed into the inner breakwater where the rockfish was found. That said, cesium concentration found in the seabed exceeds 100,000 becquerels per kg, according to Tepco.

A Tepco official told The Guardian, “Since contaminated water flowed into the Fukushima Daiichi nuclear power station port immediately after the accident, Tepco has periodically removed fish from inside the port since 2012 using fishnets that have been installed to prevent the fish from escaping the port."

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Tepco confirmed that between May 2022 and May 2023, a total of 44 fish with cesium levels above 100 becquerels per kg have been found in the Fukushima plant port, with 90% of those caught in or near the inner breakwater. Moreover, other species also had high radioactivity, such as an eel found in June 2022 carrying 1,700 becquerels per kg and rock trout with 1,200 becquerels in April 2023. 

Safety nets were installed in January 2016 to keep potentially contaminated fish inside the area.

“However, when a black rockfish with radioactive concentrations that exceed regulatory standards was caught off the coast of Soma [about 50km north of the plant] in January 2022, we began sampling again within this area in conjunction with the installation of more nets to prevent fish from leaving the port,” added the Tepco official.

Prevention methods 

After the radiation was detected, shipments of black rockfish were suspended in February 2022, and have yet to resume. The high radioactivity levels found in the fish led authorities to believe that it had escaped from the nuclear plant's port. 

Tepco is set to begin the release of more than 1.3m tonnes of treated water from the Fukushima plant next month, a process that will take decades to complete. Moreover, the UN's International Atomic Energy Agency approved the operation but has been criticized by China and others among some Pacific islands. 

Japan’s prime minister, Fumio Kishida, hit back at China’s decision to test Japanese seafood while on a recent tour of the Middle East. Kishida said on Tuesday in Doha that his government will “press for discussion based on scientific evidence”, regarding the release of the water from Fukushima.