Investigation of radionuclides in the Yenisey River floodplain systems: Relation of the topsoil radionuclide contamination to landscape features V.G. Linnik a,c , E.M. Korobova a, ⁎, J. Brown b , V.V. Surkov c , V.N. Potapov d , A.V. Sokolov a a Vernadsky Institute of Geochemistry and Analytical Chemistry, Kosygin Street 19, 119991 Moscow, Russia b Norwegian Radiation Protection Authority, Grini Naeringspark 13, P.O. Box 55, N-1332 Østerås, Norway c Moscow State University, Geographical Department, 119991 GSP-1, Moscow, Russia d Technopark, RRC “Kurchatov Institute”, Kurchatov Square, 1, 123182 Moscow, Russia abstract article info Article history: Received 4 October 2013 Accepted 4 March 2014 Available online 21 March 2014 Keywords: Yenisey Landscape 137 Cs 152,154 Eu Radionuclide burial patterns Landscape–radiometric survey and soil sampling performed in the islands of Beriozovy and Balchug (20 km downstream the Krasnoyarsk Mining and Chemical Combine), and in the Mikhin Island (180 km downstream) showed that the distribution of technogenic radionuclides depends upon the history of contamination and land- scape features of the floodplain. Contamination densities of 137 Cs appeared to be significantly higher than could be expected from global fallout (1.75–2.5 kBq/m 2 ): in 2000 the maximum value for 137 Cs in the Beriozovy Island equaled 663 kBq/m 2 , in the Balchug site — 577 kBq/m 2 and in the Mikhin Island — 518 kBq/m 2 ). 137 Cs contam- ination density was practically independent of the remoteness from the KMCC that proved its considerable mi- gration in the water-soluble or fine particulate forms. Vertical distributions of man-made nuclides in soil cores depended upon the different half-life of the studied radionuclides, the soil profile relative altitude, its structure and texture. The two main burial depths of 137 Cs activity depended upon the intensity of sedimentation and var- ied from 5 cm to 20–25 cm. In 2000 maximum contamination by 60 Co and 152,154 Eu isotopes was associated with the top layer and decreased exponentially with depth. Obtained data is believed to be important for ecological monitoring of the flood plains subjected to radionuclide contamination. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The Krasnoyarsk Mining and Chemical Combine (KMCC) was con- structed for the production of weapons-grade plutonium and is located in the hard-rock area on the right side of the Yenisey River 60 km down- stream of Krasnoyarsk. The startup of the first water cooled channel reactor was in 1958, the second one in 1961, and the third in 1964. The KMCC enterprise also included a radiochemical plant. Cooling water was discharged to the Yenisey River. In 1992 two reactors pro- ducing plutonium were shut down, and in 2010 the last reactor used also for the production of electric power, hot water supply and for heating the town of Zheleznogorsk was also decommissioned. KMCC operation in the period from 1958 to 1992 led to the contamination of the Yenisey floodplain and bottom sediments by artificial radionuclides including radioisotopes with different half-lives including 137 Cs, 60 Co, 152 Eu, and 154 Eu (the corresponding half-lives are equal to 30.2, 5.3, 13.3 and 8.6 years). After the shutdown of the two once-through reac- tors radionuclide discharge to the river decreased by a dozen times and for the period from 1975 to 2000 137 Cs disposal approximated 19,636 GBq (530 Ci) accounting for radionuclide decay (Vakulovsky et al., 2001). Initial information on the considerable radionuclide contamination of the Yenisey River was obtained at the beginning of the '70s of the pre- vious century (Vakulovsky et al., 1995), but the results of these studies at that period were not available to the scientific community for security purposes. By now there is no published data on annual discharges to the Yenisey River basin in the 1960–1975 period. Radioactivity measure- ments in the floodplain areas performed in the '70s have been sporadic (Tertyshnik, 2007). It was not earlier than the '90s when the large-scale systematic radionuclide studies of the Yenisey River floodplain from the town of Zheleznogorsk to the Kara Sea (covering the distance of over 2000 km) started. The results allowed the conclusion that maximum contamination of the bottom sediments and floodplain soils took place in the '60–'70s of the last century in areas adjacent to KMCC (Bolsunovsky, 2004; Linnik et al., 2000; Nosov and Martynova, 1996; Nosov et al., 1993; Sukhorukov et al., 2000, 2004; Vakulovsky et al., 1994, 1995). Radioactive contamination in the lower reaches of the Yenisey River down to its inflow into the Kara Sea was firstly registered at the begin- ning of the '70s (Vakulovsky et al., 1994), its traces in this segment of Journal of Geochemical Exploration 142 (2014) 60–68 ⁎ Corresponding author. E-mail addresses: linnik@geokhi.ru (V.G. Linnik), korobova@geokhi.ru (E.M. Korobova), Justin.Brown@nrpa.no (J. Brown), potapov_v@mail.ru (V.N. Potapov). http://dx.doi.org/10.1016/j.gexplo.2014.03.007 0375-6742/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Geochemical Exploration journal homepage: www.elsevier.com/locate/jgeoexp