Distribution of Am and Pu isotopes in the Curonian Lagoon and the south-eastern Baltic Sea seawater, suspended particles, sediments and biota.

Distribution trends and temporal variations of Am and Pu isotopes in the south-eastern Baltic Sea during the study period of 1999-2001 and 2011-2015 were investigated with the aim to study temporal changes of radionuclide levels in seawater, suspended particles and sediment, to estimate Am and Pu levels in marine biota and to assess the radiation doses received by the biota. The activities of Am and Pu were measured by alpha spectrometry after radiochemical purification. Pu was determined radiometrically via the ingrown daughter Am after 10-12 years of storage, while the Pu/Pu atom ratio of was measured by accelerator mass spectrometry. The Pu activities in suspended particles collected in the coastal waters of the Baltic Sea decreased by a factor of ∼3 during the study period, while they decreased about fourfold in the Curonian Lagoon. This could indicate a decrease in the influx of particles containing Pu isotopes into the Baltic Sea. While in the Curonian Lagoon, the Pu activities in the sediment samples varied insignificantly during the study periods, in the Baltic Sea, the maximum activity decreased by a factor of 6, and the mean/median values decreased by ∼4 times. The assessment tool ERICA was used to calculate the dose rates for biota. The total dose rate from all analysed radionuclides was <0.1 μGy/h, therefore no risk to organisms was identified.