Time dependence of 137Cs 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 Cs-137 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 Cs-137 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 Cs-137 concentration and the aggregated transfer factor (T-ag: calculated by dividing muscle Cs-137 concentration [Bq/kg] by soil Cs-137 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 Cs-137 in muscle may continue for some time.

Automated summary

Over the 10 years following the Fukushima nuclear accident, changes in the muscle Cs-137 concentration of wild Japanese monkeys were measured. The concentration decreased over time, but no significant difference was found between 2017 and 2020, suggesting a continued accumulation of Cs-137 in muscle.