The transboundary Irtysh River flows through the territory of three states: China, Kazakhstan and Russia.

The paper presents data on the research of the radionuclide contamination redistribution in the ecosystems of natural lakes at the Semipalatinsk test site and adjacent territories. Natural lakes, which are the research objects, are located on the territory of the test sites, in the zone of their influence, in the zone impacted by radioactive fallout or in the "background" territories. Sampling of water, bottom sediments and plants was carried out, in which the content of radionuclides ²⁴¹Am, ¹³⁷Cs, ⁹⁰Sr and ^239+240Pu was determined. Based on the obtained quantitative data, distribution coefficients (K_d) for sediments and water, as well as concentration ratio (F_V) for plants and sediments were calculated.

This article presents research findings on³H in abiotic environmental compartments, specifically, the ‘water-soil-air’ system. All of the research areas are located within the Semipalatinsk Test Site (STS): the perimeter of the ‘Degelen’ site, the riverside zone of the Shagan river and the ‘background’ area–the southeastern part of the STS (SEP). As research progressed, numerical values of³H and its species were revealed in various environmental compartments. The presence of³H was registered not only in underground nuclear test locations but also in the ‘background’ area–SEP. Maximum³H tritium concentrations in the water were detected at the ‘Degelen’ site (up to 57000±5000 Bq/kg) and the Shagan riv (up to 61500±6000 Bq/kg), in the air of the ‘Degelen’ site (up to 56±11 Bq/m³), in the soil of the ‘Degelen’ site (up to 5170±500 Bq/kg) and the Shagan riv (4100±400 Bq/kg) in the free water, at SEP (up to 1710±170 Bq/kg) in the organic constituent. Based upon all of the findings,³H was found to be readily distributed in abiotic environmental compartments depending on certain conditions. Research suggests that water plays a key role in³H migration processes in the natural system of interest. The second most but equally important constituent is soil and microorganisms of plant and animal origin living there. These assumptions are indirectly proven by research findings that show the HTO and HT air concentration dynamics depending on the sampling location.

This study aimed to assess the activity contamination levels and transfer of artificial radionuclides (²⁴¹Am, ¹³⁷Cs, ⁹⁰Sr, and ^239+240Pu) from soils to plants at underground nuclear test borehole locations in the Sary-Uzen site of the Semipalatinsk Test Site. Soil and vegetation samples were collected near warfare boreholes with different contamination patterns, conditionally "background" areas, and fallout plume sites. Peak activity concentrations in soils were recorded near borehole No. 102 for ¹³⁷Cs and near borehole No. 215 for ²⁴¹Am, ⁹⁰Sr, and ^239+240Pu. In plants, the highest ¹³⁷Cs and ⁹⁰Sr were observed near borehole No. 102, and that of ²⁴¹Am and ^239+240Pu near borehole No. 215. Transfer factors indicated that plant uptake followed the order: ⁹⁰Sr > ¹³⁷Cs > ^239+240Pu > ²⁴¹Am. Littoral-aquatic plants accumulated more ⁹⁰Sr, whereas terrestrial plants accumulated more ^239+240Pu. The maximum total exposure dose rate to vegetation reached 74 µGy/day. These findings highlight the influence of test type and contamination pattern on radionuclide behavior in ecosystems and provide a basis for radiological risk assessment in former nuclear test areas.