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):
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.
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.
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.
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.
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.