Pu and Am sorption to the Baltic Sea bottom sediments
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Pu and Am sorption to the Baltic Sea bottom sediments G. Lujanien_e • P. Benesˇ • K. Sˇtamberg K. Joksˇas • I. Kulakauskait_e
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Received: 6 August 2012 / Published online: 4 October 2012 Ó Akade´miai Kiado´, Budapest, Hungary 2012
Abstract Sorption of Am and Pu isotopes to bottom sediments of the Baltic Sea has been studied under natural and laboratory conditions. Data obtained from sequential extraction, sorption of Am(III), Pu(IV) and Pu(V) as well as oxidation state distribution experiments have shown that Pu(V) sorption mechanism includes a very fast Pu(V) reduction (reaction rate B 2.33 9 10-3 s-1) to Pu(IV) by humic substances and/or by Fe(II) to Pu(IV) and partly to Pu(III). Following reduction Pu isotopes were bound to various components of bottom sediments via ion exchange and surface complexation reactions and a slow incorporation into the crystalline structure of Fe minerals. Kinetics experiments showed that the sorption of Pu(V), Pu(IV) and Am(III) to bottom sediments from natural seawater was controlled by the inert layer diffusion process. Keywords Pu(IV) Pu(V) Bottom sediments Seawater Sorption
Introduction Radioactive contamination of the Baltic Sea arises from various sources: global fallout, the Chernobyl accident,
G. Lujanien_e (&) I. Kulakauskait_e SRI Center for Physical Sciences and Technology, Vilnius, Lithuania e-mail: [email protected]; [email protected] P. Benesˇ K. Sˇtamberg Department of Nuclear Chemistry, CTU, Prague 1, Brehova 7, Czech Republic K. Joksˇas SRI Nature Research Centre, Vilnius, Lithuania
discharges from nuclear power and reprocessing plants. Pu in the Baltic Sea is mainly derived from the global fallout after the nuclear tests, while the Chernobyl accident contributed less than 10 % of the total value estimated to be around 16–18 TBq [1]. Among the other possible sources, the inflow of contaminated North Sea seawater and nearly 250 rivers, e.g. the amount of Pu which rivers bring to the Gdansk basin of the Baltic Sea, was estimated to be 312 MBq/year whereas wet ? dry depositions constituted only 126 Bq/year [2, 3]. The activity concentrations of 239,240Pu in water samples of the southern Baltic comprise dissolved (2.8 9 10-6– 145 9 10-6 Bq/L) and suspended particles (1.6 9 10-6– 4.0 9 10-6 Bq/L) and colloidal (0.8 9 10-6–1.0 9 10-6 Bq/L) fractions [4]. The largest activities of total 239,240 Pu (150 9 10-6 Bq/L) were found for Pomeranian Bay area. The average activity concentration of 239,240Pu in the Baltic Sea water for the year 2000 was reported to be about 1.5 9 10-6 Bq/L [5]. The estimated sedimentation rate based on measured 239,240Pu in bottom sediments ranged from 0.2 to 8 mm/year, maximum activities (4–12 Bq/kg) were detected at the depth from 6 to 30 cm [6, 7]. The published data on Pu activity concentration distribution in the Baltic Sea are rather scarce and there is only one available publication on the speciation of Pu isotopes in the Baltic Sea although chemical speciation may strongly affect the sorption behavior and migration of
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