Radiocesium in seawater, sediments, and marine megabenthic species in coastal waters off Fukushima in 2012–2016, after the 2011 nuclear disaster

In bottom-sediment samples collected in 2012 from a coastal strip (∼30 km × 120 km) off the Fukushima Daiichi Nuclear Power Plant (FDNPP), radiocesium activity concentrations were generally higher south of the FDNPP, with high activity concentration patches in the north. In periodic surveys conducted at nearshore sites during 2012–2016, no clear temporal trends were observed in radiocesium activity concentrations in seawater or bottom sediment, and activity concentrations were higher in fish than in invertebrates. During 2012–2014, radiocesium activity concentrations tended to decrease in fish, but during 2012–2013 in the south, some increases were observed. Radiocesium activity concentrations were significantly higher in some fish (e.g., Okamejei kenojei) directly offshore and south of the FDNPP than in the north. Activity concentrations in fish stomach contents were significantly correlated with those in muscle tissue, suggesting that the consumption of contaminated prey contributed greatly to radiocesium contamination in demersal fish. •Distribution of radiocesium in sediment near the FDNPP was examined in October 2012 (83).•Radiocesium temporal trends in seawater and sediment from 2012 to 2016 were unclear.•A temporal increase of radiocesium in fish was observed in 2012–2013 in the south.•Among fish, radiocesium levels were significantly higher in Okamejei kenojei.•Radiocesium levels were significantly higher in fish east and south of the FDNPP.