Speakers
Description
The Southern Atlantic continental shelf of Africa is an almost blank area regarding available information on the presence of anthropogenic radionuclides, namely actinides. The coast of Namibia, part of the northern Benguela Upwelling System, was the target of the first two studies reporting 236U, 237Np, 239Pu and 240Pu in seawater [1,2]. The obtained 236U and 237Np inventories and the measured 240Pu/239Pu atom ratios in a seawater column were consistent with the global fallout source. Additionally, evidence of a different geochemical behaviour of 236U and 237Np in coastal seawater was observed.
In this work, new results on the presence of the above-mentioned radionuclides in seawater samples collected from two transects along the shelves of Angola at 10ºS and 17ºS, and one along the Namibian shelf at 22ºS, will be presented. Additionally, the profiles of 233U, 236U, 238U, 239Pu and 240Pu, in a sediment core collected at 120 m depth from the upwelling cell will be presented and discussed. Thus, more information on the Pu, U and Np contamination sources in the region and on the geochemical behaviour of 236U and 237Np in coastal seawater and sediments will be provided.
This study was carried out as a collaborative effort of different institutions and in the frame of the existing agreement between the IAEA Marine Environment Laboratories and the CNA. The seawater samples were collected during the NANSEN expedition in 2019 and the sediment core during the sampling campaign along the Namibian continental shelf in 2014. Sample processing was carried out at the CNA as well as the analysis of 236U, 237Np and 239,240Pu in the seawater samples and of 239Pu and 240Pu in the sediment core at the CNA (Seville, Spain) [3,4]. The 233U/238U and 236U/238U atom ratios in the sediment core samples were analysed on the compact AMS system MILEA at the ETH (Zürich, Switzerland) [5]. The 238U concentrations in the sediment core were determined by ICPMS at the University of Seville.
[1] M. López-Lora, E. Chamizo, M. Rožmarić, D.C. Louw, Presence of 236U and 237Np in a marine ecosystem: The northern Benguela Upwelling System, a case study, Sci. Total Environ. 708 (2020) 135222. https://doi.org/10.1016/J.SCITOTENV.2019.135222.
[2] M. Rozmaric, E. Chamizo, D.C. Louw, M. López-Lora, O. Blinova, I. Levy, B. Mudumbi, A.K. van der Plas, R. Garcia Tenorio, P. McGinnity, I. Osvath, Fate of anthropogenic radionuclides (90Sr, 137Cs, 238Pu, 239Pu, 240Pu, 241Am) in seawater in the northern Benguela upwelling system off Namibia, Chemosphere. 286 (2022) 131514. https://doi.org/10.1016/J.CHEMOSPHERE.2021.131514.
[3] M. López-Lora, I. Levy, E. Chamizo, Simple and fast method for the analysis of 236U, 237Np, 239Pu and 240Pu from seawater samples by Accelerator Mass Spectrometry, Talanta. 200 (2019) 22–30. https://doi.org/10.1016/J.TALANTA.2019.03.036.
[4] M. López-Lora, E. Chamizo, Accelerator Mass Spectrometry of 237Np, 239Pu and 240Pu for environmental studies at the Centro Nacional de Aceleradores, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms. 455 (2019) 39–51. https://doi.org/10.1016/j.nimb.2019.06.018.
[5] M. Christl, P. Gautschi, S. Maxeiner, A.M. Müller, C. Vockenhuber, H.A. Synal, 236U analyses with the ETH Zurich MILEA prototype system, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms. 534 (2023) 61–71. https://doi.org/10.1016/J.NIMB.2022.11.009.
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