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Chemistry for Sustainable Development

2003 year, number 6

Anomalies of Radioactivity on the Southern Bank of the Ysyk-Köl Lake (Kyrgyzstan)

MICHAIL S. MELGUNOV1, VSEVOLOD M. GAVSHIN1, FEDOR V. SUKHORUKOV1, IVAN A. KALUGIN1, VLADISLAV A. BOBROV1 and JEAN KLERKX2
1Trofimuk United Institute of Geology, Geophysics and Mineralogy,
Siberian Branch of the Russian Academy of Sciences,
Pr. Akademika Koptyuga 3, Novosibirsk 630090 (Russia), E-mail: mike@uiggm.nsc.ru
2International Bureau for Environmental Studies, Brusselselteenweg, 210/3 - B 3080 Tervuren, Brussels (Belgium)
Pages: 859-870

Abstract

On the basis of simultaneous gamma spectroscopic determination of radionuclides of the uranium series (238U, 226Ra, 222Rn, 210Pb) and isotopes arriving from the atmosphere (210Pbatm and 137Cs) in rocks and bottom sediments, radiogeochemical background of land sediments represented mainly by granitoid weathering products was obtained (35-55 Bq/kg), along with evidences of the hydrodynamic mode of sediment formation within the recent century. Three types of radioactivity anomalies exceeding the background by one-two orders of magnitude were revealed on the southern bank of the lake: natural uranium and radium anomalies; industry-related radium anomalies (ash obtained from burning uranium-bearing coal); industry-related uranium anomalies. Sedimentation rate was estimated in the deep water region using the decay of 210Pbatm activity to be 0.2-0.4 mm/year during the recent century. On the basis of uranium to radium ratio, it was established that the fraction of uranium in deep water sediments arriving from the lake water is 1.5-2 times higher than the fraction arriving with the suspension. One of the sources of uranium in the lake water was erosion of uranium-bearing coal within the geological time scale. A layer enriched with radium was discovered near the bank at the depth of 5 to 20 cm. The presence of high-temperature mineral mullite in the sediment is an evidence of the penetration of industry-related radioactive ash into the lake in amounts that can hardly be dangerous for the biogeosystem of the lake Ysyk-Kul.