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

Data on concentrations and distribution of tritium in soils of the “Atomic” Lake excavation explosion area of Semipalatinsk Nuclear Test Site (Kazakhstan, East Kazakhstan oblast) are discussed. The concentrations of tritium in surface soil horizons and in soil profiles have been determined in the bulk soil samples and in different particle-size fractions. Tritium concentration in soils reaches 240 000 Bq/kg. A correlation has been found between tritium and europium concentrations in soils. Presumably, tritium formation is controlled by two mechanisms. One of them is the neutron activation process, i.e., nuclear reactions with lithium, boron, and nitrogen isotopes present in the soil; the other mechanism is related to the capture of tritium that was initially in the charge of mineral particles formed upon condensation from the red-hot explosion zone.

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.

The timely identification of areas where man-made radionuclides migrate through water streams is highly important for the territory of the former Semipalatinsk Test Site since the aquatic environment is currently a source of secondary contamination of environment. This article presents research findings on radioactively contaminated Lake Kishkensor located at the Semipalatinsk Test Site territory. As a result of this research, a new locally contaminated spot was discovered in the vicinity of the “Balapan” test site. Lake Kishkensor was found to be contaminated with man-made ³H and ⁹⁰Sr. The ³H activity concentration in surface waters reached 430 kBq/L, and the concentration of ⁹⁰Sr reached 100 Bq/L. In the sediments, the ³H activity concentration reached 700 kBq/kg, while that of ⁹⁰Sr and ^239+240Pu reached 310 Bq/kg and 250 Bq/kg, respectively. Ground water was found to be a source of surface water and sediment contamination. The monitoring results showed that the contamination level of the lake largely depended on the season and the inflow of contaminated ground water.

Tightly bound tritium (TBT) in soil is poorly studied in terms of its bioavailability. This paper presents the results of long-term studies (2018 through 2023) on the bioavailability of tightly bound tritium in soil. Field studies were conducted in the epicentral zones of the Semipalatinsk test site (STS), using dominant and subdominant species. Laboratory tests were carried out in a greenhouse using different vegetable crops. The TBT concentration in the soil over the research period (2018-2023) significantly decreased from 57 to 28 кBq kg^-1 (a total decrease is 29 кBq kg^-1). TBT losses due to nuclear decay amounted to 14 кBq kg^-1 (48 %) and due to leaching, they were 15 кBq kg^-1 (52 %). It was found that the main leaching factor is water regime. The tritium concentration of soil solution is correlates with soil moisture (r = 0.47, p = 0.05). The obtained linear regression model can explain 48 % of the variation in tritium concentration in soil solution depending on soil moisture. The assessment of species differences in the uptake and incorporation of TBT from the soil under laboratory conditions, as well as the established values of the OBT_plant/HTO_soil и OBT_plant/TFWT_plant ratios indicate that plant roots are able to mobilize TBT into bioavailable forms. Thus, TBT in soil can be converted to a bioavailable form and migrate. This study is of great importance for comprehension of the mechanisms of tritium migration in the soil-plant system, which can help predict its behavior not only in ecosystems of STS but also in radioactive waste disposal areas.