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

Cs-137 and Pu239+241 data in seawater, sediment and biota from the regional seas of Asia-Pacific extending from 50degrees N to 60degrees S latitude and 60degrees E to 180degrees E longitude based on the Asia-Pacific Marine Radioactivity Database (ASPAMARD) are presented and discussed. Cs-137 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. Pu239+141 levels in surface seawater are much lower, with a median of about 6 mBq/m(3). Pu239+240 appears to be partly scavenged by particles and is therefore more readily transported down the water column. As with seawater, Pu239+240 concentrations are lower than Cs-137 in surface sediment. The median Cs-137 concentration in surface sediment is 1.4 Bq/kg dry, while that Of Pu239+140 is only 0.2 Bq/kg dry. The vertical profiles of both Cs-137 and Pu239+241 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 Cs-137 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 Cs-137 and Pu239+240 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 Cs-137 and Pu239+240 in particular, and other anthropogenic as well as natural radionuclides in seawater, sediment and biota from the Asia-Pacific regional seas. (C) 2004 Elsevier Ltd. All rights reserved.