米国沖のマグロから微量セシウム 原発事故の影響と発表
共同通信(2012年5月29日)

 東京電力福島第1原発事故に伴う微量の放射性セシウムが、米西海岸沖のクロマグロから検出されたと米スタンフォード大などの研究チームが28日付の米科学アカデミー紀要電子版に発表した。

 チームは「マグロが太平洋を横断し、原発事故による放射性物質を運んできたのは明らかだ」としている。食べても健康への影響は心配ないレベルだが、事故の大きさをあらためて示す結果だ。

 昨年8月、米カリフォルニア州サンディエゴ沖でクロマグロ15匹を捕獲。調べるとセシウム134を1キログラム当たり4ベクレル、セシウム137を同6・3ベクレル検出した。いずれも昨年3月の原発事故時に日本沿岸にいて、海流に乗って移動してきたらしい

 事故前の2008年に捕獲した別のクロマグロを調べると、半減期が2年と比較的短いセシウム134は検出されず、セシウム137の量もごくわずかだった。

 東電は、原発事故で大気中に放出された放射性物質の量は90万テラベクレル(テラは1兆)で、このうち1万8千テラベクレルが海に流れ込んだとみている。
http://www.kyodonews.jp/feature/news05/2012/05/post-5772.html

【参考】

Tuna contaminated with Fukushima radiation found in California
Scientists amazed that bluefins swimming in Pacific five months after Japanese disaster contained tiny amounts of caesium

Justin McCurry in Tokyo and agencies
guardian.co.uk, Tuesday 29 May 2012 05.59 EDT

Bluefin tuna contaminated with radiation believed to be from Fukushima Daiichi turned up off the coast of California just five months after the Japanese nuclear plant suffered meltdown last March, US scientists said.

Tiny amounts of caesium-137 and caesium-134 were detected in 15 bluefin caught near San Diego in August last year, according to a study published on Monday in the Proceedings of the National Academy of Sciences journal.

The levels were 10 times higher than those found in tuna in the same area in previous years, but still well below those that the Japanese and US governments consider a risk to health. Japan recently introduced a new safety limit of 100 becquerels per kilogram in food.
(クロマグロで発見された汚染レベルとしては去年よりも10倍高いが、日本とアメリカ政府が健康影響があると考えているレベルよりもまだかなり低い。日本は最近食品安全基準100ベクレル/kgを発表している)
The timing of the discovery suggests that the fish, a prized but dangerously overfished delicacy in Japan, had carried the radioactive materials across the Pacific ocean faster than those conveyed by wind or water.
(発見のタイミングは、重宝されているが危機的に日本で乱獲されている魚が風や水で運ばれるよりも速く太平洋を縦断して放射性物質を運んできたことを示唆している)

The researchers, led by Daniel Madigan at Stanford University, said they had found evidence that the fish had been contaminated at "modestly elevated" levels with caesium. The chemical was released into the ocean in the wake of the accident at Fukushima Daiichi on 11 March 2011.

Madigan told Reuters: "I wouldn't tell anyone what's safe to eat or what's not safe to eat. It's become clear that some people feel that any amount of radioactivity, in their minds, is bad and they'd like to avoid it. But compared to what's there naturally ... and what's established as safety limits, it's not a large amount at all."

The fish are thought to have been exposed to radiation for about a month before beginning their journey east across the Pacific. They were found to contain 4 becquerels per kilogram of caesium-134 and 6.3 becquerels per kilogram of caesium-137, the report said. A 2008 study of fish in the area found no evidence of caesium-134, which is produced only by nuclear power plants and weapons, and caesium-134 only at levels that naturally occur in the environment.

(魚は太平洋を東へ向かう旅の始まりの1ヵ月前に汚染されたと見られている。汚染は、セシウム134が4ベクレル/kg、セシウム137が6.3ベクレルであったと伝えられた。2008年の当該地域の魚の調査では、原発か核兵器でのみ生成されるセシウム134は発見されておらず、セシウム134は自然界に存在するレベルでしかなかった。)
The results "are unequivocal. Fukushima was the source", said Ken Buesseler of the Woods Hole Oceanographic Institution, who played no part in the research.

Japan's chief cabinet secretary, Osamu Fujimura, conceded that the findings suggested the monitoring of radiation levels in fish outside Japanese waters may have to be stepped up.

The spawning and migratory patterns of bluefin tuna indicate that the issue of contaminated fish will be confined to Pacific coastlines.

Bluefin spawn only in the western Pacific, off the coasts of Japan and the Philippines. Some juvenile or adolescent fish migrate east to the coast of California coast and remain there to fatten up.

Scientists say they do not believe contamination will linger in large fish capable of swimming farther afield, as they are able to metabolise and excrete radioactive substances.

The fish examined in the US study weighed an average of 15 pounds. They had shed some of the radionuclides during their journey but had been unable to flush them out altogether.

"We were frankly kind of startled," said Nicholas Fisher, an expert at Stony Brook University in New York who took part in the study. "That's a big ocean. To swim across it and still retain these radionuclides is pretty amazing."

The operator of the Fukushima Daiichi plant, Tokyo Electric Power, estimates that 18,000 terabecquerels of radioactive materials flowed into the Pacific after the accident, either in the form of fallout, or through mixing with water that leaked from the facility. A terabecquerel is equal to 1tn becquerels.
http://www.guardian.co.uk/world/2012/may/29/tuna-contaminated-radiation-fukushima-california

失礼します。
にほんブログ村 環境ブログ 原発・放射能へ
にほんブログ村

人気ブログランキング