RADIOISOTOPES

In Namie Town, Fukushima Prefecture, decontamination was carried out after the Fukushima Daiichi Nuclear Power Station accident. After remediation, the restricted residential area and the area preparing for the lifting of evacuation orders in the eastern part of Namie Town were lifted, and residents started returning home beginning on March 31, 2017. Various self-consumed crops, including homegrown agricultural crops and edible wild plants, were collected from the decontaminated fields and surrounding areas in 2019 and 2020. Activity concentrations of radiocaesium were measured in 181 samples of grain, potatoes, beans, vegetables, and fruits. Internal radiation exposure to humans from ingestion of the crops were calculated. Activity concentrations of ¹³⁷Cs in the homegrown agricultural crops ranged from 0.18 to 46 Bq kg⁻¹ fresh weight, which were all below the standard limit of 100 Bq kg⁻¹, while in the wild plants collected from around the fields ¹³⁷Cs ranged from 3.2 to 175 Bq kg⁻¹ fresh weight. The additional internal radiocaesium radiation dose for adult males in 2020 from ingestion of the various self-consumed crops was 0.032 mSv, accounting for approximately 5％ of the total additional internal and external radiation dose of 0.64 mSv due to the accident. The internal radiation dose from the intake of the homegrown agricultural crops, excluding wild plants, was 0.012 mSv, which was about 1/3 of that from the intake of both self-consumed crops and wild plants, and well below 1 mSv.