Concentrations of radioactive cesium from the Fukushima nuclear disaster in wild game animals in nine eastern Japanese prefectures have been dropping, but remain higher than the government-mandated limit for shipment to market in many areas
The upper limit for cesium concentrations in meat is 100 becquerels per kilogram. Shipments of seven types of wild game from areas of Fukushima, Miyagi, Yamagata, Ibaraki, Tochigi, Gunma, Chiba and Niigata prefectures have remained restricted since the March 2011 meltdowns at the Fukushima No. 1 nuclear plant as cesium contamination has yet to fall consistently below the government-set maximum.
For example, wild boar meat examined at a processing plant in Nakagawa, Tochigi Prefecture, registered as much as 1,100 becquerels per kilo in fiscal 2012, and a high of 340 becquerels in fiscal 2015.
According to ecology expert and Chiba University associate professor Masashi Murakami, the cesium fallout was deposited on fallen leaves by repeated rainfall. However, as time passes the radioactive element will be absorbed by clay particles in the forest soil, removing it from animals' food sources. As such, says Murakami, cesium levels in wild game animals will fall faster than the element's natural decay rate.
However, "there are large differences between the cesium concentrations of individual animals, so it will take a long time to 'consistently fall under the maximum concentration' as the government demands to lift shipment restrictions," says Murakami. For example, "even in Nakagawa, it may take 10 more years."
A Ministry of Health, Labor and Welfare official in charge of the issue stated, "The only way for shipments to go ahead again is for every animal to be tested."