Lateral and temporal variations in Fukushima Dai-ichi NPP-derived 134Cs and 137Cs in marine sediments in/around the Sado Basin, Sea of Japan

Lateral and temporal profiles for concentrations of Cs-134 and Cs-137 were examined in marine sediments obtained from coastal and offshore areas on the Sea of Japan-side of central Honshu. In 2013, concentrations declined sharply from an estuarine (30 Bq/kg-dry for Cs-134) to offshore areas. In the offshore Sado Basin, the concentration of short-lived Cs-134, which was not detected (< 0.3 Bq/kg-dry) in 2010, was 1-15 Bq/kg-dry in 2011-2013. Discharged riverine materials affected by radiocesium derived from the Fukushima Dai-ichi Nuclear Power Plant have been delivered to this offshore basin.