The time-dependent transfer factor of radiocesium from soil to game animals in Japan after the Fukushima Dai-ichi nuclear accident

Since the Fukushima Dai-ichi accident, monitoring of tissues from hunted game animals ensures compliance with the standard food limits for radionuclides in Japan. We quantified the transfer of 137Cs from contaminated land to game animals using the Aggregated transfer factor (Tag = activity concentration in meat [Bq kg–1 fw]/amount in soil [Bq m–2]) of 137Cs for Asian black bear, wild boar, sika deer, green pheasant, copper pheasant and wild duck, collected between 2011 and 2015. Open data sources were used from Fukushima, Miyagi, Ibaraki, Tochigi, and Gunma prefectures. Our initially compiled data showed that the maximum reported 137Cs activity concentration in wild boar after the Fukushima Dai-ichi accident were lower than those reported after the Chernobyl accident. The geometric mean Tag values (m2kg–1 fw) of 137Cs in 2015 for Asian black bear, wild boar, sika deer and copper pheasant were similar (1.9–5.1) × 10–3 while those for green pheasant and wild duck were about 1 order of magnitude lower at (1.0–2.2) × 10–4. Effective half-lives were 1.2–6.9 y except for sika deer and copper pheasant where no decreases were found. In contrast to the Chernobyl accident, no seasonal change occurred in the meat 137Cs activity concentrations of the wild animals during the study period.