Time dependence of 137 Cs contamination in wild Japanese monkeys after the Fukushima Daiichi nuclear accident.

Over the 10 years immediately after the Fukushima Daiichi nuclear accident, we measured the changes in the muscle 137 Cs concentration (Bq/kg) of wild Japanese monkeys living in Fukushima City, which is located approximately 70 km from the Fukushima Daiichi Nuclear Power Plant. The muscle 137 Csconcentration, which was observed at a maximum of 13,500 Bq/kg immediately after the accident, had decreased to several hundred Bq/kg 10 years later. The muscle 137 Cs concentration was significantly related to the soil contamination levels (10,000-30,000, 30,000-60,000, 60,000-100,000, and 100,000-300,000 Bq/m 2 ), sex, age class (immature, mature), body weight (> 5000 g, 5000-10,000 g, < 10,000 g), and seasons (the cold period from December to April, the warm period from May to November).The value of muscle 137 Cs concentration and the aggregated transfer factor (T ag : calculated by dividing muscle 137 Cs concentration [Bq/kg] by soil 137 Cs deposition density at the capture site [Bq/m 2 ]) apparently decreased with time for several years. However, post hoc pairwise comparisons showed no difference from 2017 to 2020, and the accumulation of 137 Cs in muscle may continue for some time.