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To China from Fukushima Flounder: 'We're Healthy, Happy, and Clean'

TEPCO's team is raising flounder in treated water and its tests confirm the tritium stays well below international standards without accumulating in the fish.



IAEA Director General Grossi feeds flounder in a tank with treated water at the Fukushima Daiichi Nuclear Power Plant in July 2023. (Pool photograph)

Dear people of China, we are flounder. As you know, the treated water discharge from Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant into the Pacific Ocean has begun. 

Your government officials, however, have repeatedly objected to this. They have stated that the discharge of nuclear-contaminated water into the ocean threatens human life and health. However, these concerns are unfounded.

We are not just any flounder. Instead, we are flounder who have been living in seawater in a tank containing treated water for a year. We are in good health and order. Could there be any more convincing evidence of the safety of this water? 

Evidence over theory, as they say. Rest assured, scientific measurements show that tritium has neither accumulated nor concentrated in us fish. On behalf of all Japanese fish species, we thank you in advance for your understanding.


Sound and Healthy

These flounder live in an indoor facility on the Fukushima Daiichi Nuclear Power Plant grounds. TEPCO began its flounder breeding project at the end of September 2022. At that time, there were approximately 800 farmed flounder. When they arrived a year ago, they were baby flounder around 16 cm long.

Flounder are being bred in a tank of seawater mixed with treated water containing tritium (© Sankei by Shohei Nagatsuji)

TEPCO started by dividing the number of flounder into four equal groups. Two tanks contained "regular seawater." Treated water was added to seawater in the other two tanks to reduce the level to less than 1,500 becquerels per liter ("treated water tanks"). The volume of water in each tank was approximately 4,000 liters.

This writer visited the nuclear power plant in late August 2023, close to one year after the start of the breeding program. On-site manager Kazuo Yamanaka greeted me upon arrival.

Yamanaka and his team have consistently compared growth and activity between flounder in the regular and treated tanks. Results show no difference, with survival rates at 99% for both and sizes ranging from 20 to 25 centimeters.

Live Streaming

There is an underwater camera installed in the tank. Anyone interested can access TEPCO's treated water portal site for a live view of the flounder.

Typically flounder stay quite still. However, as Yamanaka explains, "During feeding time, they suddenly jump into life, which some viewers look forward to."


Fishery officials have also inspected the breeding tanks. International Atomic Energy Agency (IAEA) Director General Raphael Grossi even fed the flounder when he visited the plant in July.

Tritium in Living Organisms

Through breeding experiments, the project closely monitors the behavior of tritium in the bodies of marine fish and shellfish. As part of this, in October 2022, the team conducted tritium uptake and discharge tests on the flounder. 

In these experiments, they transferred flounder in the regular tank to the treated water tank (approximately 1,250 becquerels). Then the team collected body fluids at six intervals from one hour to 144 hours following the transfer. 

This uptake test confirmed that the concentration of tritium contained in body fluids increases over time. Although the tritium concentration in flounder in tanks of 1,300 becquerels of treated water rises to approximately 1,100 in 24 hours, it then levels off.

Some flounder spent 144 hours in the treated water tank. Then they returned to normal seawater. The team subsequently tracked changes in tritium concentration in their body fluids at five intervals between one to 72 hours.

The results of this test demonstrated that:

(1) Tritium concentration does not exceed that of the breeding environment.

(2) Within that environment, tritium concentration reaches equilibrium after a certain period.

In other words, TEPCO's team confirmed that tritium does not accumulate in fish. Nor does it reach concentrations above the breeding environment.

Tests on Ezo-abalone, a shellfish, and gulfweed show similar results. Both were faster than flounder in terms of uptake and discharge, at one hour each, respectively.

Ezo-abalone are being reared in treated water containing tritium to which seawater has been added at TEPCO's Fukushima Daiichi site. (© Sankei by Shohei Nagatsuji)

Intramuscular Concentration?

Tritium in living organisms can be present in either body fluids or organically bound to carbon and other substances in proteins. Therefore, the project team is also examining the organic-bound tritium concentration in flounder.

They tested flounder taken from a treated water tank of 1,250 becquerels of tritium per liter. However, they found only a minimal uptake. It took approximately 150 days from the start of the test for the slow accumulation to show signs of leveling. When it did so, it was measured at only around 200 becquerels.


Their results show tritium uptake into the muscles of flounder is likely to remain at about 20% of the amount taken up by body fluids.

End of Initial Discharge

On August 24, the first discharge of treated water into the ocean began. It continued slowly until September 11.

Internationally, the observed standard is up to 60,000 becquerels of tritium per liter of discharged water. TEPCO, however, has diluted the concentration even further using a more stringent standard. First TEPCO mixes the treated water containing tritium with seawater. Then it discharges the diluted treated water it one kilometer offshore through an undersea tunnel. Using this method, TEPCO has lowered the tritium output to 1,500 becquerels per liter, or 1/40th of the international standard.

The IAEA has confirmed that the release meets international safety standards from a scientific perspective. Despite this, the Chinese government immediately proceeded with a total ban on imports of all Japanese marine products.

One can practically hear the conversations between the flounder and the Ezo abalone.

"It seems the IAEA and TEPCO have signed a cooperative agreement regarding our breeding demonstration test," said a flounder. "That is good news. I guess that means we have made our international debut," the abalone responded. "I hope this test will show the world that the discharge of treated water does not harm marine life and ecosystems."


(Read the column in Japanese.)

Author: Shohei Nagatsuji

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