Spatiotemporal distribution of radioactive cesium released from Fukushima Daiichi Nuclear Power Station in the sediment of Tokyo Bay, Japan

The spatial and temporal distribution of ¹³⁴Cs and ¹³⁷Cs released from Fukushima Daiichi Nuclear Power Station in the Tokyo Bay sediments were investigated. The total radioactivity of ¹³⁴Cs and ¹³⁷Cs detected in the Tokyo Bay sediment ranged from 240 to 870 Bq/kg-dry in the estuary of Arakawa River, but the activities detected in other sites were about 90 Bq/kg-dry or less. These results suggested that radioactive cesium, which precipitated to the ground, was carried to the river along with clay particles by rainfall and transported to the estuary. The vertical distribution of radioactive cesium showed that it invaded deeper than estimated based on the accumulation rate of the sediment. It was described that the vertical distribution of radioactive cesium was affected by physical mixing of sediments by tidal current, flood, and bioturbation of benthos. (author)