Radioactive cesium measured in samples of silt taken from Tokyo Bay has increased to 1.5-13 times the amount detected in similar samples last August, according to a survey conducted by Kinki University.
The cesium is believed to have entered the bay via rivers after its release from the Fukushima No. 1 nuclear power plant following last year's accidents there.
The research group led by Prof. Hideo Yamazaki analyzed silt samples taken on April 2 at three places in the bay, including one place near the estuary of the Arakawa river.
Samples taken from a one-meter-deep layer of silt contained 7,305-27,213 becquerels per square meter, up from 578-18,242 becquerels announced on Aug. 20 last year after a similar survey.
Samples taken from a six-centimeter- deep layer contained 321-397 becquerels per kilogram of silt, up from the previous 75-320 becquerels.
Cesium apparently accumulated in the silt of rivers and entered the bay gradually, the researchers said.