Radiation Contamination of Tokyo Bay Already Happening

From Asahi Shinbun (2/8/2012):

東京湾の海底で、放射性セシウムが深さ２０センチ以上の泥まで達していることが近畿大の調査でわかった。地上の土壌では５センチ以内に９割以上とどまるが、海底では逆に深い方が濃くなる場所もあった。

A survey by Kinki University has revealed that radioactive cesium has reached the depth of 20 centimeters of the ocean mud in Tokyo Bay. More than 90% of radioactive cesium stays within 5 centimeters from the soil surface on land, but on the ocean floor there are spots where the deeper soil contains more radioactive cesium.

　セシウムを含む海底の泥を食べた生物が、泥の中に排泄（はいせつ）するためとみられる。山崎秀夫教授（環境解析学）は「海洋汚染への影響を考えると、深く埋まるのが早まるのはいいことだ」としている。

It may be because of the feces of the organisms in the mud that eat the mud containing cesium. Professor Hideo Yamazaki (environmental analysis) says, "It is a good thing that radioactive cesium gets buried deep quickly, when we consider the impact on marine contamination."

　山崎教授は昨年８月、東京湾の荒川河口付近の４カ所で海底の泥を掘って調べた結果、放射性セシウムが深さ２４～２６センチのところでも確認された。別の場所では１２～１４センチでの濃度が最も高かった。セシウムはいずれも東京電力福島第一原発から出たとみられる。

Professor Yamazaki collected the mud on the ocean floor at 4 location near the mouth of River Arakawa that flows into Tokyo Bay last August. Radioactive cesium was found in the mud 24 to 26 centimeters deep. In other locations, the highest concentration of radioactive cesium was found between 12 to 14 centimeters deep. Cesium is considered to have come from Fukushima I Nuclear Power Plant.

I'm not sure if it's a good thing.

Asahi's article, since the full version is only available to paid subscribers, doesn't mention the density of radioactive cesium. But Professor Yamazaki was featured in the NHK documentary on marine contamination (aired on 1/15/2012), and in that documentary the mud collected from the mouth of Edogawa River was found with 872 becquerels/kg of radioactive cesium. (I'll write about the NHK documentary later.)

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#Radioactive Nori in Tokyo Bay

Someone was tweeting that radioactive cesium has been found in dried sheets of "nori" (seaweed) made in Chiba Prefecture and Kanagawa Prefecture, on Tokyo Bay. So I looked for the original information, which I figured must have come from the Fisheries Agency.

And so I found it there.

The Fisheries Agency publishes the result of the survey of radioactive materials (iodine, cesium only) in marine products including seaweeds. In the latest result published on December 21 for the items reported since October, radioactive cesium has been found in dried "nori" in:

Kanagawa Prefecture - 1 sample, at 11 becquerels/kg

Chiba Prefecture - 6 samples, 11, 27, 25, 16.5, 5.6, 17.7 becquerels/kg respectively

Nori grown and harvested in Tokyo Bay, called "Edomae nori", commands super premium. One sheet of Edomae nori usually fetches over 10 yen a sheet at wholesale (US 13 cents), and used mostly in gourmet sushi restaurants.

The levels are not supposed to be causing negative effect on health as per the Japanese government; the government's provisional safety limit for radioactive cesium is 500 becquerels/kg.

By the way, this level is set to be lowered to 100 becquerels/kg on the April Fool's Day next year which is the first day of fiscal 2012 in Japan. Serious.

I've never seen the news of radioactive cesium detection in nori in the mainstream media at all. Without Twitter, I wouldn't have known about it. I'm curious to know how radioactive cesium traveled from Fukushima to Tokyo Bay. The government has claimed that the Kuroshio Current would prevent the spread of radioactive materials south of Ibaraki.

Judging by the reaction to my Japanese tweet, there are many others like me who didn't know about the detection.

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