Gavshin V M, Melgunov M S, Sukhorukov F V, Bobrov V A, Kalugin I A, Klerkx J
Institute of Geology UIGGM, Russian Academy of Sciences, Siberian Branch, Novosibirsk, Russia.
J Environ Radioact. 2005;83(1):61-74. doi: 10.1016/j.jenvrad.2005.02.012. Epub 2005 Apr 20.
The Kadji-Sai abandoned field of U-bearing brown coal on the southern coast of Lake Issyk-Kul (Kyrgyzstan) poses a threat of radioactive pollution to the world's fifth deepest and second largest pristine highland lake. The valleys of ephemeral streams in the lake catchment are filled with coarse-grained sand and clay, with a background U--Ra activity of 35--55 Bqkg(-1). High activity areas vs. this background come from three sources: (1) scarce outcrops of uraniferous brown coal and mining wastes containing fragments of this coal with (238)U/(226)Ra ratios of 0.8 due to uranium losses through weathering; (2) manmade anomalies caused by a radioactive waste dump, where U was extracted from the ash of coal burnt at a coal-fired power plant. As a result, the (238)U/(226)Ra ratios become 0.15--0.25; (3) six catch pools terraced below the mine, where U activity decreases downslope, and (238)U/(226)Ra ratios reach 150--200. Uranium lost in the extraction process may have been retained on the terraces. The distribution pattern of radionuclides in the bottom sediments of the lake is controlled by water depth and offshore distance. The upper section of homogeneous limy--argillic deposits in the lake center remains undisturbed by currents, as indicated by regular sub-exponential distribution of atmospheric (137)Cs and (210)Pb(atm). Sedimentation rate in the lake center for the past century, found from (210)Pb, was 0.32 mmyr(-1). (238)U/(226)Ra in deep-water sediments was about 3. The activity of uranium adsorbed by sediments from the lake water was estimated by subtraction of the Ra-equilibrium component from the total U activity. Thus, the flux of dissolved U to the bottom sediments was as 2.07 x 10(-7)gcm(-2)yr(-1). The upper section of near-shore deposits was disturbed by currents, with (137)Cs and (210)Pb(atm) more or less uniformly distributed in this layer. Peaks of (226)Ra and (210)Pb occur at different depths from 5 to 20 cm below the sediment surface, with (238)U/(226)Ra ratios 0.28--0.44. The presence of mullite in these sediments indicated that radioactive ash penetrated into the lake in the past. At present, (226)Ra in the ash is buried under a non-radioactive cap.
位于吉尔吉斯斯坦伊塞克湖（Issyk-Kul）南岸的卡吉-赛（Kadji-Sai）废弃含铀褐煤田，对世界第五深、第二大的原始高山湖泊构成放射性污染威胁。该湖集水区内季节性溪流的山谷中布满粗砂和黏土，铀-镭本底活度为35 - 55贝可勒尔每千克。与该本底相比，高活度区域来自三个源头：（1）含铀褐煤露头稀少，以及含有该煤碎片的采矿废料，由于风化导致铀损失，其铀-238/镭-226比值为0.8；（2）放射性废料堆造成的人为异常，在那里铀是从燃煤发电厂燃烧煤炭产生的灰烬中提取的。结果，铀-238/镭-226比值变为0.15 - 0.25；（3）矿场下方六级梯田状集水池，铀活度沿下坡方向降低，铀-238/镭-226比值达到150 - 200。在提取过程中损失的铀可能留存于梯田上。湖泊底部沉积物中放射性核素的分布模式受水深和离岸距离控制。湖泊中心均匀的石灰质-泥质沉积物上部未受水流扰动影响，大气铯-137和铅-210大气组分呈规则的次指数分布表明了这一点。根据铅-210测定，过去一个世纪湖泊中心的沉积速率为每年0.32毫米。深水沉积物中的铀-238/镭-226约为3。通过从总铀活度中减去镭平衡组分来估算沉积物从湖水中吸附铀的活度。因此，溶解态铀向底部沉积物的通量为2.07×10⁻⁷克每平方厘米每年。近岸沉积物上部受水流扰动，铯-137和铅-210大气组分在该层中分布或多或少较为均匀。镭-226和铅-210的峰值出现在沉积物表面以下5至20厘米的不同深度处，铀-
