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 134Cs and 137Cs 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 134Cs) to offshore areas. In the offshore Sado Basin, the concentration of short-lived 134Cs, 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.