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.