Studies of Np and Pu in the marine environment of Swedish-Danish waters and the North Atlantic Ocean

The long-lived anthropogenic radionuclides Np-237, Pu-239 and Pu-240 were determined in marine environmental samples (seaweed and seawater) collected from Swedish-Danish waters and the North Atlantic Ocean at various locations on different occasions during the period 1991-2001. The measurements were performed with sector field Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and conventional alpha spectrometry. The Np-237 activity concentrations in Fucus vesiculosus and surface seawater from the Swedish west coast and Danish waters ranged from 0.16 +/- 0.02 to 1.02 +/- 0.09 mBq kg(-1) (dry weight) and 0.65 +/- 0.02 3 to 1.69 +/- 0.02 mBq m(-3), respectively, depending on the location and sampling year. Most of the Np-237 in these waters is believed to originate from the Sellafield nuclear reprocessing plant, with some contribution from global fallout. The Pu-240/Pu-239 atomic ratios in F. vesiculosus samples are reported in this study with an overall average of 0.17 +/- 0.03. The Np-237 and (PU)-P-239 activity concentrations observed in surface seawater collected in North Atlantic waters ranged from 0.16 +/- 0.01 to 0.62 +/- 0.08 mBq m(-3) and from 0.64 +/- 0.05 to 4.27 +/- 0.08 mBq m(-3), respectively, and the Np-237/Pu-239 atomic ratios were a good indicator of conservative behaviour of Np in marine waters. (c) 2005 Elsevier Ltd. All rights reserved.