Anthropogenic actinides in seawater and biota from the west coast of Sweden

Abstract: The assessment of the origin of the anthropogenic contamination in marine regions impacted by other sources than global fallout is a challenge. This is the case of the west coast of Sweden, influenced by the liquid effluents released by the European Nuclear Reprocessing Plants through North Sea currents and by Baltic Sea local and regional sources, among others. This work focused on the study of anthropogenic actinides (${}^{236}$U, ${}^{237}$Np and ${}^{239,240}$Pu) in seawater and biota from a region close to Gothenburg where radioactive wastes with an unknown composition were dumped in 1964. To this aim, a radiochemical procedure for the sequential extraction of U, Np and Pu from biota samples and the subsequent analysis of ${}^{236}$U, ${}^{237}$Np, ${}^{239}$Pu and ${}^{240}$Pu by Accelerator Mass Spectrometry was developed. The method was validated through the study of two reference materials provided by the International Atomic Energy Agency (IAEA): IAEA-446 (Baltic Sea seaweed) and IAEA-437 (Mediterranean Sea mussels). The ${}^{233}$U$/{}^{236}$U atom ratio was also studied in the seawater samples. The obtained results indicate that the North Sea currents and global fallout are the major sources for ${}^{236}$U, ${}^{237}$Np and ${}^{239,240}$Pu to the studied area, with any clear evidence of other local sources. Complementary, information on the Concentrations Factors (CF) in biota was obtained, for which the available information is very scarce. For seaweed, CF values of $(4.1 \pm 1.1) \times 10^{3}$, $88 \pm 51$ and $70 \pm 20$ have been obtained for Pu, Np and U, respectively. Lower CF values of $(3.6 \pm 1.2) \times 10^{2}$, $37 \pm 15$ and $15.1 \pm 5.2$ for Pu, Np and U, respectively, have been obtained for mussels.