Fukushima Across the Pacific

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Fukushima Across the Pacific

Radiation in the air spread far and wide, and was even detectable, though barely, on other continents, while radiation in the ocean is spreading more slowly but inexorably.

Let’s make it clear: the release of radioactive contamination from the Fukushima NPP to the environment — the air, the land, and the ocean — is a massive disaster. 

There’s no other way to describe it. Radiation in the air spread far and wide, and was even detectable, though barely, on other continents, while radiation in the ocean is spreading more slowly but inexorably.

We know that some of the fish caught off Japan have been too contaminated to be sold for human consumption, and that wide expanses of farmland in Japan have been contaminated as well. But what effects can be expected overseas?

 

Dr. Ken Buesseler of The Woods Hole Oceanographic Institute (WHOI) has authored or co-authored several of the most informative studies of Fukushima ocean impacts. The illustration above is from one of his presentations, and shows how Fukushima radioactive releases to the world’s oceans compare to those from Chernobyl and weapons testing, as well as to natural radiation.

As you can see, while Fukushima released quite a lot of Cs137 to the oceans, the amount appears to be somewhat less than that from Chernobyl, about 1/10 of that from global testing, and only a tiny fraction of the natural radiation (mainly Uranium 238 and Potassium 40) that has always been there. WHOI is reportedly in the process of testing water samples taken from the ocean offshore off northern California, and hopefully the results will not be long in forthcoming.

The author, an ocean scientist, admits to getting a bit snarky, and we think his assessment of the risk to people is possibly not nuanced enough, but he does a good job of refuting some of the wilder speculation.

What about the radioactive tuna?

Many people are concerned about radioactive cesium from Fukushima that has been detected in migratory Pacific bluefin tuna caught near California, which had approx. 4.0 Bq/kg of Cs 134 and 6.3 Bq/kg of Cs 137 (Japanese regs allow 100 Bq/kg, the EU allows 600 Bq/kg, while the US allows 1200 Bq/kg of Cs 137 and Cs134 combined.

The original study is here:
Madigan, et al: Pacific bluefin tuna transport Fukushima-derived radionuclides from Japan to California

One of the best sources of information on the risks this contamination poses can be found in this paper:
Fisher, et al: Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood

Among the important takeaways are:

–“…doses in all cases were dominated by the naturally occurring alpha-emitter 210Po and that Fukushima-derived doses were three to four orders of magnitude below 210Po-derived doses.”

–If a subsistence fisherman, who eats more fish than an average consumer, ate 124 kg of the contaminated tuna that was caught in 2011 over the course of a year, the additional committed effective (i.e. lifetime) dose they would get from the cesium in the fish, even taking the higher risk from internal emitters into account, would be 4.7 μSv (microsieverts). They would get more than 600 times this from the Po210 in the fish, and 2.8 mSv (millisieverts) from all the radiation in the fish, including K40. On the other hand, an average consumer who ate this tuna regularly for a year would receive about a 0.9 μSv lifetime dose.

–Pacific bluefin tuna caught off California in August, 2012 were found to have less than half the levels of Cs of those caught in August, 2011; doses to human consumers would be comparably smaller.

–It is often stated that any dose of radiation, no matter how small, carries a health risk; this can only be estimated statistically because it has been impossible to detect directly at very low doses.

Assuming an excess relative risk of fatal cancer of about 5% per Sv of radiation dose, the doses to the fishermen from eating a lot of this fish “…can be estimated to result in two additional fatal cancer cases per 10,000,000 similarly exposed people.” That is, it would increase a person’s probability of fatal cancer by 0.00002%.

Some scientists have proposed good reasons to adopt a higher risk coefficient, 10% per Sv instead of 5%, in which case the probability would be 0.00004% instead. Other potential health consequences from Cs would lie in a similar range of probability.

Conclusions
We try to avoid saying what is “safe” or “unsafe,” but this is a vanishingly small risk. These fish and other species need to be continually monitored, however, in the event the contamination increases for some reason.

There are important gaps in our understanding of the foodchain interactions as fish cross the Pacific, but the evidence indicates that these tuna spent time in the ocean plume close to Japan in 2011 while it was still very dense and that’s why they ingested as much Cs as they did.

Fukushima continues to release contamination to the ocean, but the amount per year as estimated by the scientists cited earlier is about 1/300 of what was released during the first few months after the disaster started in 2011 (about 0.1 Pbq now vs about 30 PBq in 2011).

This continuing release poses an ongoing threat to marine species and the environment off the coast of Japan, one that shows no sign of abating anytime soon. But from what we now know, and particularly taking into account the known rate of bioaccumulation for fish — they accumulate 50-100 times of the Cs present in the water they swim through– its contribution to radiation in migratory species that reach the US is likely to be imperceptible.

In a later post we will talk about the radioactive contamination in the ocean off Japan itself, which presents a much more painful picture.

Attached link

http://blog.safecast.org/2014/01/fukushima-across-the-pacific/

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