Following up this article ..Video of black substance
Similar substance found in Toukatsu Chiba.
The radiation level is 0.36 microSv/h at 10cm from the substance.
The person who found this tweeted like this below.
Momoiro_Usagi
@momousagi2011
現時点では同じものかどうかわかりませんが、今の家に約10年住んでいて一度も見たことのない真っ黒な埃で、普通の埃は風で舞いますがべっとりとしていて黒い雨を連想しました。Source
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Now I don’t know if it’s exactly the same thing as in Minami soma, but I haven’t seen such black “dust” though I’ve been living here for 10 years. Normal dust flies by the wind but this black substance is wet and greasy. It reminds me of black rain after Hiroshima and Nagasaki.
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Prof.Hayakawa from Gunma university talks, it’s everywhere in Toukatsu, and even in Tokyo.
Iori Mochizuki