Radioactive Cesium Contamination of Sika Deer in Oku-Nikko Region of Tochigi Prefecture in Central Japan

137Cs concentrations in the muscles and the rumen and rectal contents of sika deer and in dwarf bamboo and other plants as the main winter food source of the sika deer were investigated in the Oku-Nikko, Tochigi Prefecture, Japan. The 137Cs concentration of the 5-year residual winter leaves of dwarf bamboo from 2012 decreased over the years, but the Tag of dwarf bamboo from the soil to dwarf bamboo did not change. The average 137Cs concentrations of the muscles of the deer decreased from the winter of 2012 to that of 2016, and those of the rumen contents and the rectal contents collected from 2012 to 2014 have decreased over time. The 137Cs concentration of the rectal contents was 2.4 times that of the rumen contents and 3 times the muscle, suggesting that sika deer may excrete most of 137Cs taken from foods while concentrating it in the digestive tract. The Tag has been decreasing with year: from the dwarf bamboo to the deer muscles, 21.5–31.3 m2 kg−1 dwt, and from the soil to the deer muscles, 0.02–0.01 m2 kg−1 dwt.