Distribution and inventory of fallout Pu and Cs in the sediment of the East Sea of Korea

Sediment samples were collected from the Ulleung Basin in the East Sea of Korea and analyzed for 239, 240 Pu, 238Pu and 137Cs concentrations and excess 210Pb. The apparent sedimentation rate was estimated to be 0·069 cm year -1 for Station 1 sediment and 0·061 cm year -1 for Station 2 sediment. From depth profiles, the maximum concentrations of 239, 240 Pu and 137Cs appeared at 2–4 cm depth in sediments on the continental slope and at 2–3 cm depth in the Ulleung Basin, corresponding to the deposits laid down in the years 1950–1975. The inventories of 239, 240 Pu and 137Cs were estimated to be 59·4 and 338·6 Bq m -2 for Station 1 sediment and 65·5 and 247·4 Bq m -2 for Station 2 sediment. The activity ratios of 238Pu/ 239, 240 Pu in sediments were found to be within the narrow range of 0·028–0·052 with a mean value of 0·041. No significant changes in 239, 240 Pu/ 137Cs ratios occur with depth in the East Sea sediments. The activity ratios of 239, 240 Pu/ 137Cs in the surface sediment were higher than the ratio due to global fallout.