New insights into actinides sources to the Baltic Sea
Dr Mercedes López-lora1, Mats Eriksson1, Grzegorz Olszewski2, Elena Chamizo3, Per Törnquist1, Håkan Pettersson1, Marie Karlsson1, Patric Lindahl4, Victoria Lérida3, José María López-Gutiérrez3
1Linköping University, Linköping, Sweden, 2University of Gdańsk, , Poland, 3Centro Nacional de Aceleradores, Sevilla, Spain, 4Swedish Radiation Safety Authority, , Sweden
The Baltic Sea is a semi-enclosed and shallow sea with an increased accumulation of radioactive materials compared to open oceans. The main sources of artificial radionuclides to this marine environment are: i) fallout coming from atmospheric nuclear weapon testing (1945-1980), ii) fallout coming from Chernobyl accident (1986), iii) liquid releases form Sellafield and La Hague nuclear reprocessing facilities transported through the North Sea, iv) authorized radioactive discharges occurring during the routine operation of nuclear installations in the Baltic Sea region and v) possible leakages from the multiples radioactive wastes dumping sites within this marine region . Because of the specific situation and characteristic of this marine environment, the Baltic Sea is one of the most studied areas regarding the distribution of radioactive radionuclides. However, radionuclides such us 233U, 236U and 237Np, possibly only mensurable by AMS, have been scarcely studied and their sources to the Baltic Sea remain unknown. Recent studies have revealed the still open question about 236U sources to the Baltic Sea .
The aim of this work is the study of actinides (i.e. 233U, 236U, 237Np and Pu isotopes) from a series of samples (i.e. seawater, sediments, seaweed and biota) collected from different regions at the Baltic Sea in order to get better insights into their input sources to this oceanic environment. Two study areas are included here: i) an area close to Gothenburg, which has not been previously studied even though radioactive wastes were dumped there in 1964, and ii) the Tvären Bay, directly impacted by the liquid releases from Studsvik Nuclear Plant whose actinides isotopic composition have not been documented. We have found out that: i) there are not significant evidences of possible leakages from the dumped wastes at the Gothenburg area; and ii) our results from Tvären clearly indicate an important contribution of Studsvik releases, especially for 236U, 239Pu and 240Pu. Dated sediment cores from Tvären Bay have been used to study the historical releases. Furthermore, the study of the isotopic composition of Pu in those sediments is extended to the most minor Pu isotopes, 241Pu and 244Pu.
 J. Herrmann, T.K. Ikäheimonen, E. Ilus, G. Kanisch, M. Lüning, J. Mattila, S.P. Nielsen, I. Osvath, I. Outola, Baltic Sea Environment Proceedings No. 117 Radioactivity in the Baltic Sea, HELCOM Themat. Assess. Balt. Sea Environ. Proc. (1999).
 J. Qiao, H. Zhang, P. Steier, K. Hain, X. Hou, V. Vartti, G.M. Henderson, M. Eriksson, A. Aldahan, G. Possnert, R. Golser, Baltic Sea revealed by multi-isotope fingerprints 236U, Nat. Commun. (2021). https://doi.org/10.1038/s41467-021-21059-w.
Mercedes López-Lora finished her PhD thesis in December 2019 in the group of AMS at the Centro Nacional de Aceleradores (CNA, University of Seville, Spain). Currently, she holds a postdoctoral position at the Linköping University. Therein, she is part of the radioecology group at the Department of Health, Medicine and Caring Sciences. Her research focuses on the analysis of actinides by AMS in environmental samples. Now, she is involved in different projects for the study of Baltic Sea. She works in the different stages along this kind of studies: sampling, sample preparation, AMS technique and discussion of the results.