In the background, from left, the No. 1, 2, 3, and 4 reactor buildings of the Fukushima No. 1 Nuclear Power Plant are seen, in Okuma, Fukushima Prefecture, on Oct. 31, 2016. In front are tanks used to store contaminated water. (Mainichi)

The Ministry of the Environment announced on Aug. 14 that it has lost about 10 kilograms of contaminated soil that was shipped from a sender in the city of Fukushima after the 2011 nuclear disaster.

The ministry says it probably disposed of the soil mistakenly. The contamination level of the soil is low and it's highly unlikely to affect human health, ministry officials said.

The soil packed in small cardboard boxes was sent to the ministry on Nov. 8 and 16, 2011, by home delivery service from Fukushima and included the sender's name. A letter attached to the box read, "The ministry should keep and dispose of the soil, which was taken at my house in the city of Fukushima." At that time, the radiation dose of the soil was 0.6 microsieverts per hour and the concentration of radioactive materials was estimated to be about 4,000 becquerels per kilogram. These levels are currently estimated at 0.2 microsieverts and 2,000 becquerels, respectively, according to the ministry.

The soil had been kept in an aluminum case in the ministry building but there is a high possibility that officials threw it away when they disposed of disused articles in January this year. Commenting on the incident, Environment Minister Masaharu Nakagawa said, "It's really regrettable that there's a chance the soil was discarded due to inappropriate management."

(Japanese original by Norikazu Chiba, Science & Environment News Department)