Yomiuri: Cesium in Body Will Halve in 1.5 Years in Wild Animals Even If They Eat Contaminated Food Everyday

Yomiuri Shinbun may have made a fool of itself by summarizing the finding by a university researcher regarding the biological half-life of radioactive cesium in a very exaggerated (and inaccurate) way.

If you read the article, it's rather embarrassingly clear that "wild animals" are lab mice, and "eating contaminated food everyday" is drinking cesium-laced water only once. It is possible that the researcher's paper made a connection between a mouse and a wild animal, and drinking water once and eating contaminated food every day, and Yomiuri Shinbun, in its eagerness to bring the good tidings to the general public in Japan, omitted the connection in the article.

Oh well. Many of my Japanese twitter readers who read the article are saying, "What can you expect from a pro-nuke newspaper like Yomiuri?" or "Gomiuri (garbage seller)?"

From Yomiuri Shinbun (11/18/2011):

東京電力福島第一原発事故直後に野生動物に大量に取り込まれた放射性セシウム１３７の量は、動物が原発周辺の食物を摂取していても約１年半ごとに半減し、最初の５年間で８分の１以下になる可能性が高いことを大阪大学の中島裕夫助教が突き止めた。

Hiroo Nakajima of Osaka University has found that there is a high possibility that a large amount of radioactive cesium-137 ingested by wild animals right after the Fukushima I Nuclear Power Plant accident may halve every 1.5 years, falling to one-eighths after the first 5 years even if the animals keep eating the food around the nuclear power plant.

原発周辺地域の野生動物や住民の内部被曝(ひばく)の状況などを知る手がかりになるもので、１７日、神戸市で開かれている日本放射線影響学会で発表した。

It will provide a clue to the internal radiation exposure of wild animals and people in the areas near the plant. His research was published in the meeting of the Japan Radiation Research Society in Kobe City on November 17.

中島助教は、マウスに半減期が約３０年のセシウム１３７を含んだ水（体重１グラム当たり１キロ・ベクレル＝１匹当たり２８キロ・ベクレル）を一回だけ飲ませた後、時間経過とともに体内に残る量を調べた。

Nakajima fed mice with water with cesium-137 whose half life is about 30 years (1 kilo-becquerel/1 gram of live weight, or 28 kilo-becquerels per mouse) once, and studied the amount of cesium remaining in the body over time.

心臓や腎臓など大半の臓器では、摂取後すぐにピークを迎えたが、１週間後には２５分の１以下、２週間後には１２０分の１以下になった。

In most organs such as heart and kidney, the amount of cesium peaked right after ingesting the water. However, it dropped to one-25th in one week, and to one-120th in 2 weeks.

So?

These wild animals (eh... mice) are likely to have been eating contaminated food and drinking contaminated water ever since March 11. So did people, like villagers in Iitate-mura or town folks in Namie-machi, for quite some time after the March 11 accident. They ate the vegetables they grew, and drank water from their wells, on assurance from the experts like Dr. Yamashita.

Here's the ICRP's chart, showing how the one-time episodic intake of 1000 becquerels of radioactive cesium is handled by the body, compared to the continuous, daily intake of low-level (10 becquerels and 1 becquerel) radioactive cesium (from ICRP publication 111, page 21):

(The researcher could have just put up this chart for his presentation, instead of feeding lab mice with cesium water.)

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