Health effect by radioactive contaminants of wild Japanese monkeys in Fukushima city. Research achievements for 4 years and future challenges

The objective of this study was to determine the change in concentration of radiocesium ¹³⁴Cs and ¹³⁷Cs over time in the muscle of Japanese monkeys inhabiting Fukushima City located 70 km from the Fukushima Daiichi Nuclear Power Plant (NPP), and their health effect of radioactive materials. Cesium concentration in the muscle of monkeys was 6,000-25,000 Bq/kg in April 2011 and decreased over 3 months to around 1,000 Bq/kg. However, the concentration increased again to 2,000-3,000 Bq/kg in some animals during winter before returning to 1,000 Bq/kg in April 2012. After that, the concentration decreased gradually up to the present date. From 2012, we carried out a one-year hematological study on a population of Fukushima City and the Shimokita Peninsula located approximately 400 km from the NPP as a control. Total muscle cesium concentration was below the detection limit in all Shimokita monkeys. Compared with Shimokita monkeys, Fukushima monkeys had significantly low white and red blood cell counts, hemoglobin, hematocrit (p<0.01), and the white blood cell count in immature monkeys showed a significant negative correlation with muscle cesium concentration (p<0.05) in 2012. After 2013, blood cell counts were increased gradually over time, these results suggest that the exposure to some form of radioactive material contributed to hematological changes in Fukushima monkeys. (author)