3100 Bq/kg of #Radioactive Cesium from Wild Mice in Kawauchi-mura, Fukushima

Kawauchi-mura is inside the former evacuation zones where the volunteers including small children planted rice over the weekend. The location where the mice were caught is 6 to 7 kilometers south of the rice farm.

NHK reports (5/14/2012):

東京電力福島第一原子力発電所からおよそ３０キロの山林で捕獲した野生のネズミから３１００ベクレルの放射性セシウムが検出され、専門家は野生生物に対する影響を継続的に調べる必要があるとしています。

3100 becquerels/kg of radioactive cesium was detected from wild mice caught in the mountains about 30 kilometers from Fukushima I Nuclear Power Plant. The experts say it will be necessary to continuously monitor the effect [of radiation] in wild animals.

茨城県つくば市にある独立行政法人の森林総合研究所は、福島第一原発からおよそ３０キロの福島県川内村三ッ石地区と、７０キロの茨城県北茨城市関本町小川地区のいずれも集落から離れた山林でそれぞれ去年１０月と１２月に野生のアカネズミを捕獲しました。

In October and December last year, the Forestry and Forest Products Research Institute, an independent administrative corporation [under the Ministry of Agriculture, Forestry and Fisheries] caught wild Japanese mice in Mitsuishi District of Kawauchi-mura in Fukushima Prefecture, about 30 kilometers from Fukushima I Nuclear Power Plant, and in Ogawa District in Sekimoto-cho, Kita-Ibaraki City in Ibaraki Prefecture, about 70 kilometers from the plant. The mountains where the mice were caught are away from the residential areas.

そして、合わせて１２匹の体内に蓄積した放射性セシウムの濃度を調べた結果、１キログラム当たりの平均で、川内村で捕獲したネズミからは３１００ベクレル、北茨城市で捕獲したネズミからは７９０ベクレル検出されました。

The researchers measured the radioactive cesium density in 12 mice. From the mice caught in Kawauchi-mura, average 3100 becquerels/kg of radioactive cesium was detected, while average 790 becquerels/kg was detected from mice caught in Kita-Ibaraki City.

捕獲場所の空気中の放射線量は、川内村が１時間当たり３．１１マイクロシーベルト、北茨城市が０．２マイクロシーベルトで、放射線量が高い場所ではネズミの放射性物質の濃度も高くなる傾向にありました。

Air radiation levels of the locations where the mice were caught were 3.11 microsieverts/hour in Kawauchi-mura and 0.2 microsievert/hour in Kita-Ibaraki City. The higher the air radiation levels were, the higher the density of radioactive materials in the mice.

調査結果について、放射線の動物への影響を研究する放射線医学総合研究所の久保田善久サブリーダーは「ネズミは人間と同じ程度、放射線への感受性が高い。野生生物に対する放射性物質の影響を継続的に調べる必要がある」と話しています。

Commenting on the result, Yoshihisa Kubota of the National Institute of Radiological Sciences, who studies the effect of radiation on animals, says, "Mice have about the same sensitivity to radiation as humans. We need to continuously monitor the effect of radioactive materials on wild animals."

The Forestry and Forest Products Research Institute also did the measurement of radioactive cesium in earthworms in Kawauchi-mura. The result was released in February this year, and they found 19,500 bq/kg of radioactive cesium in earthworms in the same Mitsuishi District of Kawauchi-mura where the layer of dead leaves was found with 319,000 Bq/kg of radioactive cesium and the soil (taken from the surface to 5 centimeter deep) was found with 20,900 Bq/kg of radioactive cesium.

20,900 Bq/kg of radioactive cesium from soil taken from the surface to 5 centimeters deep would translate to 1,358,500 Bq/m2. But the only area in Kawauchi-mura where the human habitation is still restricted (though entering the area is not prohibited) is inside the 20-kilometer radius. So, this location in Mitsuishi District is, as with the rest of Kawauchi-mura, in the areas newly designated as "getting ready for the return of the residents".

1,358,500 Bq/m2, or half that considering only cesium-137, would be a "permanent control zone" in Chernobyl. But in the post-Fukushima Japan, the annual cumulative external radiation of 20 millisieverts is "safe", and the national government is "decontaminating" so that the residents can return to the former evacuation zones in Fukushima. Sooner or later the residents will have little choice but return, as the government doesn't intend to keep paying the compensation now that it's set to effectively take over TEPCO.

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