Cesium level in Tokyo Bay spikes, but still safe

May 23, 2012

The concentration of waterborne radioactive cesium in central Tokyo Bay was six times the level prior to last year's nuclear disaster, but far below the legal standard for safe bathing, the science ministry said May 22.

This is the first time the Ministry of Education, Culture, Sports, Science and Technology has released a partial result of cesium level measurements taken at 15 or more locations in Tokyo Bay.

The latest data release pertains to only one sampling site, lying roughly midway between Kawasaki Port in Kanagawa Prefecture and Sodegaura in Chiba Prefecture.

In the sample taken April 18, a liter of seawater contained 0.0065 and 0.0098 becquerel of cesium-134 and cesium-137, respectively.

The latter figure is 6.1 times higher than the 0.0016 becquerel of cesium-137 per liter of seawater sampled in 2009 by the Japan Coast Guard in a nearby area.

The government's safety standard for the combined concentration of waterborne cesium-134 and cesium-137 in bathing areas is 50 becquerels per liter.

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Local people check tidelands at Sanbanse, Tokyo Bay, one month after the Great East Japan Earthquake of March 11, 2011. (Asahi Shimbun file photo)

Local people check tidelands at Sanbanse, Tokyo Bay, one month after the Great East Japan Earthquake of March 11, 2011. (Asahi Shimbun file photo)

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  • Local people check tidelands at Sanbanse, Tokyo Bay, one month after the Great East Japan Earthquake of March 11, 2011. (Asahi Shimbun file photo)

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