137Cs and 239+240Pu levels in the Asia-Pacific regional seas

Abstract

137Cs and 239+240Pu data in seawater, sediment and biota from the regional seas of Asia-Pacific extending from 50° N to 60° S latitude and 60° E to 180° E longitude based on the Asia-Pacific Marine Radioactivity Database (ASPAMARD) are presented and discussed. 137Cs levels in surface seawater have been declining to its present median value of about 3 Bq/m 3 due mainly to radioactive decay, transport processes, and the absence of new significant inputs. 239+240Pu levels in surface seawater are much lower, with a median of about 6 mBq/m 3. 239+240Pu appears to be partly scavenged by particles and is therefore more readily transported down the water column. As with seawater, 239+240Pu concentrations are lower than 137Cs in surface sediment. The median 137Cs concentration in surface sediment is 1.4 Bq/kg dry, while that of 239+240Pu is only 0.2 Bq/kg dry. The vertical profiles of both 137Cs and 239+240Pu in the sediment column of coastal areas are different from deep seas which can be attributed to the higher sedimentation rates and additional contribution of run-offs from terrestrial catchment areas in the coastal zone. Comparable data for biota are far less extensive than those for seawater and sediment. The median 137Cs concentration in fish (0.2 Bq/kg wet) is higher than in crustaceans (0.1 Bq/kg wet) or mollusks (0.1 Bq/kg wet). Benchmark values (as of 2001) for 137Cs and 239+240Pu concentrations in seawater, sediment and biota are established to serve as reference values against which the impact of future anthropogenic inputs can be assessed. ASPAMARD represents one of the most comprehensive compilations of available data on 137Cs and 239+240Pu in particular, and other anthropogenic as well as natural radionuclides in seawater, sediment and biota from the Asia-Pacific regional seas.