Tokyo Electric Power Co.’s revelation that massive amounts of radioactive water are flowing into the Pacific further raised fears about the harm to marine life.

Tepco estimated that between May 2011 and this month, a staggering 40 trillion becquerels of radioactive tritium, 20 trillion becquerels of cesium and 10 trillion becquerels of strontium may have flowed into the sea in groundwater from under the Fukushima No. 1 nuclear complex.

The Nuclear Regulation Authority will set up an expert panel Sept. 6 to study the effect on marine life, focusing on tritium, which cannot be removed even with the advanced liquid processing system that Tepco plans to restart to clean contaminated water used to cool the crippled reactors as early as next month. ALPS extracts most radioactive materials from tainted water — but not tritium.

What is tritium?

Tritium is a radioactive isotope of hydrogen with a half life of approximately 12 years. Around 99 percent of tritium exists in the form of water and it emits very weak beta particles that can be stopped even with plastic wrap.

A small amount exists in nature, for instance in rainwater, rivers and oceans, as well as in the human body. On average, the body of a man weighing 65 kg contains about 100 becquerels of tritium, experts estimate.

According to the Citizens’ Nuclear Information Center, a Tokyo-based anti-nuclear organization, 1 kg of rainwater contains about 1 to 3 becquerels of tritium. That level was about 100 becquerels per kilogram during the 1960s due to fallout from nuclear experiments around the globe, the group said.

What hazard does tritium pose to human health?

The potential harm of tritium to humans is much smaller than that of radioactive cesium — the major focus of concern following the three nuclear meltdowns at the No. 1 power plant in 2011. Experts say exposure to tritium is roughly one-thousandth as harmful compared with radioactive cesium.

The Citizens’ Nuclear Information Center said that if a person were to drink 1 liter of water tainted with 2 becquerels of tritium every day for one year, the total radiation exposure would amount to 0.00004 millisieverts.

Because tritium exists mainly in water, it does not accumulate in any specific body organ and is discharged quickly through urine, experts say. In the human body, tritium levels drop by half in around 10 days, they say.

What about marine life?

The impact on marine creatures, for now, is believed to be small, Jota Kanda, oceanographer at Tokyo University of Marine Science and Technology, told The Japan Times on Friday.

The tritium-tainted groundwater discharged from the No. 1 plant into the Pacific was diluted by seawater, he said. Although the projected amount of tritium that leaked into the ocean is frightening, judging from water samples it likely won’t pose a great risk to human health if a person were to eat fish caught outside the man-made harbor of the crippled nuclear plant, according to Kanda.

Just as with humans, tritium is discharged from fish through urine, he said.

What is more alarming, Kanda said, is contamination from strontium-90, which tends to accumulate in bones and can cause bone cancer or leukemia, and from cesium-137 and -134, which appear to remain in the ecosystem.

Does the government’s standard sampling survey detect tritium in fish produce?

No. The Fisheries Agency only checks for radioactive iodine, cesium and strontium, and has no plan to expand the survey to tritium, one of its officials said, adding that detecting tritium from fish samples is almost impossible with the technology the agency currently has.

How contaminated are fish caught off Tohoku, and has the situation worsened recently?

Results from the Fishery Agency’s sampling tests show no significant increase in contamination level of fish caught off the coast.

Just a few samples — mostly bottom fish caught off Fukushima and freshwater fish in the prefecture — exceeded the government limit of 100 becquerels of radioactive cesium per kilogram.

However, fish caught in the No. 1 plant’s harbor have been found to be highly contaminated with radioactive cesium, according to Tepco’s sampling data. For instance, a spotbelly rockfish caught July 4 contained 177,000 becquerels per kilogram of cesium, and a jacopever also caught in July contained 180,000 becquerels.

The utility set up a containment fence around the harbor to limit contamination of the sea.

According to Tepco’s regular sampling test conducted in July outside the harbor but within 20-km of the plant, a few fish were discovered to exceed the 100-becquerel cesium limit and had levels of between 100 and 400 becquerels per kilogram.

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