Fate of Radioactive Contamination in Fukushima Fish

suneko/CC BY-SA 2.0

In the wake of the nuclear disaster at Fukushima, experts declared the marine impacts "worse than Chernobyl" as 80 percent of the radiation released ended up in the Northwest Pacific Ocean.

Marine chemist Ken Buesseler of the Woods Hole Oceanographic Institution (WHOI) published the latest analysis of the fate of the radioactive particles released in the Fukushima meltdown in the 26 October edition of Science magazine. Buesseler and his team analyzed data on the testing of fish contamination released by the Japanese Ministry of Agriculture, Forestry and Fisheries (MAFF).

Fish Still on Tokyo Tables

I was coincidentally in Tokyo last week on business, and observed fish on the table as often as ever in the de facto capital of this nation of seafood aficionados. The Japanese government tightened limits on the allowable levels of radioactive Cesium in fish to 100Bq/kg in April 2012, after a temporary allowance had set levels at 500Bq/kg -- a level which the Japanese Ministry of Health, Labor and Welfare (MHLW) calculated as safe, even for long-term consumption, based on an annual safe dose of 5mSv.*"

The good news in the WHOI study: the "vast majority of fish caught off the northeast coast of Japan" meet the 100Bq/kg limits for safe consumption by the public.

Fukushima Fish Still Feeding on Radioactive Cesium

The fish caught closest to ground zero of the nuclear accident, off the coast of Fukushima prefecture, measure highest for levels of radioactive cesium isotopes.

Unlike the coal-power associated mercury, which accumulates continuously in fish, the radioactive cesium is routinely eliminated by fish metabolism. Therefore, if there is no active source of re-contamination, it would be expected that radioactive levels in fish would have declined by this time.

Buesseler reports that the highest contamination levels are observed in bottom-feeding fish. He concludes:

there may be a continuing source of radionuclides into the ocean, either in the form of low-level leaks from the reactor site itself or contaminated sediment on the seafloor. In addition, the varying levels of contamination across fish types points to complex methods of uptake and release by different species, making the task of regulation and of communicating the reasons behind decision-making to the fish-hungry Japanese public all the more difficult.

Bruesseler and the WHOI team will present their findings at a scientific symposium in November which will help set the priorities for further studies on the effects of the event that most seriously damaged the hopes of advocates for nuclear industry sustainability. As part of the event, the scientists offer free registration for a public colloquium on Fukushima on 14th November 2012, available in simultaneous translation in English and Japanese.

*Background information on safe limits of exposure to radioactivity:
The 100Bq/kg limit is more in line with recommendations of the International Commission on Radiological Protection (ICRP) that members of the public be exposed to not more than 1mSv/year (averaged over 5 years). That figure is calculated as above background levels of 2.4mSv/year from cosmic radiation, terrestrial radiation, and inhalation and ingestion of common radioactive particles such as radon; it excludes radiation from necessary medical testing. Typical limits for nuclear industry workers allow 20mSv/year averaged over 5 years, with not more than 50mSv in any single year. (source: World Nuclear Organization)

Tags: Fish | Fishing | Japan | Nuclear Power

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