Abstract
This article presents the results of a study of the spatial distribution and occurrence forms of trace elements in the bottom sediments of the Karabulak Stream, located within the Degelen Mountains of the Semipalatinsk Test Site. Bottom sediment samples were collected at 19 points along the main stream channel and its four tributaries. A sequential extraction method was used to determine the occurrence forms of chemical elements. This method allows for the isolation of water-soluble, exchangeable, weakly specifically sorbed, organic matter-bound, iron and manganese oxideand hydroxide-bound, and residual forms. Quantitative determination of elements was performed using ICP-MS and ICP-AES. It was established that the distribution of trace elements in the bottom sediments is characterized by significant spatial heterogeneity due to the hydrological characteristics of the stream and the anthropogenic impact of the former test site. Exceedances of Clarke values were detected for a number of elements, primarily uranium, beryllium, molybdenum, and cadmium. The highest concentrations of Be, Sr, and Cd were observed in the upper reaches of the stream, while Mo and U contents increased in the lower reaches. Uranium in the bottom sediments of the main channel was shown to be predominantly in a watersoluble form, indicating its high migration capacity and potential environmental hazard.