Journal of Environmental Radioactivity 214–215 (2020) 106157 Available online 11 January 2020 0265-931X/© 2020 Published by Elsevier Ltd. Impact of Saharan dust events on radionuclides in the atmosphere, seawater, and sediments of the northwest Mediterranean Sea M.K. Pham a, * , E. Chamizo b , M. Lop� ez-Lora b , J. Martín c , I. Osvath a , P.P. Povinec d a IAEA-Environment Laboratories, Monte Carlo, 98000, Monaco b Centro Nacional de Aceleradores, Universidad de Sevilla, Isla de la Cartuja, 41092, Sevilla, Spain c CADIC-CONICET, Bernardo Houssay 200, Ushuaia, 9410, Argentina d Faculty of Mathematics, Physics and Informatics, Comenius University, SK-84248, Bratislava, Slovakia A R T I C L E INFO Keywords: Radionuclides 137 Cs 236 U Pu isotopes Monaco air Water column Sediment DYFAMED station NW mediterranean ABSTRACT In February 2004, anthropogenic radionuclides ( 137 Cs, 236 U, 239 Pu and 240 Pu), transported from the Sahara Desert, were observed in the Monaco air, and later in water and sediment samples collected at the DYFAMED site in the northwest (NW) Mediterranean Sea. While 236 U and 137 Cs in Saharan dust particles showed a high sol- ubility in seawater, Pu isotopes were particle reactive in the water column and in the sediment. The impact of the Saharan deposition was found at 0–1.0 cm of the sediment core for 236 U and 137 Cs, and between 1.0 and 1.5 cm for Pu isotopes. The excess of 236 U was observed more in the water column than in the sediment, whereas the 239þ240 Pu total inventories were comparable in the water column and the sediment. This single-day particle event represented 72% of annual atmospheric deposition in Monaco. At the DYFAMED site, it accounted for 10% ( 137 Cs) and 15% ( 239þ240 Pu) activities of sinking particles during the period of the highest mass fux collected at the 200 and 1000 m water depths, and for a signifcant proportion of the total annual atmospheric input to the NW Mediterranean Sea (28–37% for 137 Cs and 34–45% for 239þ240 Pu). Contributions to the total 137 Cs and 239þ240 Pu sediment inventories were estimated to be 14% and 8%, respectively. The Saharan dust deposition phenomenon (atmospheric input, water column and sediment) offered a unique case to study origin and accu- mulation rates of radionuclides in the NW Mediterranean Sea. 1. Introduction Radionuclides found in ground-level air are of natural or anthropo- genic origin. Naturally occurring radionuclides include cosmogenic ra- dionuclides such as 7 Be and 22 Na, and radiogenic radionuclides such as 210 Pb and 210 Po, which represent radon decay products that emanate from the earth’s crust. Anthropogenic radionuclides including 137 Cs, isotopes of plutonium, and 236 U have been introduced to the atmosphere via nuclear weapons tests, releases from nuclear reprocessing facilities, and accidents such as Chernobyl and Fukushima (e.g. Livingston and Povinec, 2000, 2002). After their release to the atmosphere, radionu- clides rapidly adsorb on micron-sized aerosols and their behavior in the ground-level air is driven by the aerosols (Pham et al., 2003, 2005, 2011; Masson et al., 2009; Sýkora et al., 2012; Povinec et al., 2012; Hirose and Povinec, 2015). Atmospheric radionuclides are deposited onto the land and sea sur- face by wet and dry deposition. In this way, the terrestrial and marine environments are labelled by radionuclides that can be used as tracers of environmental processes. Radionuclide activities and their isotopic ra- tios in the environment can vary due to changes in radionuclide sources, such as releases from nuclear installations or radon emanating from soil. Variability in radionuclide activities in the atmosphere can also arise from processes such as soil resuspension or biomass burning (Amiro et al., 1996; Wotawa et al., 2006; Povinec et al., 2012; Hirose and Povinec, 2015). Saharan dusts events, which can be observed in the atmosphere of the southern Europe, are associated with the re-suspension source term. This transport of dust particles from northern Africa to Europe can have a substantial impact on the atmospheric processes in the southern Europe. It has also been identifed as an important pathway for particle delivery into surface seawater of the northwest (NW) Mediterranean (Moulin et al., 1997; Lee et al., 2002, 2003; Pham et al., 2003, 2005; Menut et al., 2009; Ternon et al., 2010). Similar dust events originating from Mongolian and Chinese deserts have also been reported in Japan * Corresponding author. E-mail address: m.pham@iaea.org (M.K. Pham). Contents lists available at ScienceDirect Journal of Environmental Radioactivity journal homepage: http://www.elsevier.com/locate/jenvrad https://doi.org/10.1016/j.jenvrad.2020.106157 Received 7 October 2019; Received in revised form 2 January 2020; Accepted 2 January 2020