Radioecological state of the environment in the area of the former Semipalatinsk Nuclear Test Site

Radioactive contamination of the environment in the former Semipalatinsk nuclear test site (Kazakhstan) is caused by the deposition and long-term retention of long-lived radionuclides in soil, water and vegetation, which poses potential risks to ecosystems and public health. The study aimed to assess the levels of contamination of soil, water and vegetation with americium-241, cesium-137 and plutonium-239/240 radionuclides in areas of different radiation risk in the former Semipalatinsk nuclear test site. Radiation and environmental monitoring were conducted at 12 control points using spectrometric analysis to determine the specific activity of the specified radionuclides in environmental samples. The study revealed pronounced differences in the content of radionuclides in soil, water and vegetation in areas with different levels of radiation risk. The maximum concentrations of americium-241 (0.55 ± 0.03 Bq/kg), cesium-137 (1.83 ± 0.15 Bq/ kg) and plutonium-239/240 (0.012 ± 0.0015 Bq/kg) were recorded in the extreme radiation risk zone, while in the least contaminated areas, their levels were 4-7 times lower. In water bodies, the highest activity was recorded for cesium-137, with a concentration of 5.22 ± 0.2 Bq/l, which significantly exceeds the permissible limits. Significant accumulation of all three radionuclides was detected in the vegetation: Am-241 to 1.6 ± 0.3 Bq/kg, Cs-137 to 2.2 ± 0.1 Bq/kg, Pu-239/240 to 0.9 ± 0.1 Bq/kg. The highest levels were recorded in areas of extreme and maximum risk, mainly in pasture cereals. The analysis of the vertical distribution of radionuclides showed their differentiation by depth: Cs-137 and Am-241 were concentrated in the upper soil layer (0-10 cm), while Pu-239/240 partially migrated to 15-20 cm, which confirmed the risk of their inclusion in the trophic chains and the need for further monitoring. The data obtained can be used to plan measures for the environmental remediation of contaminated areas, regulate the agricultural use of pastures and ensure the radiation safety of the population