Abstract
This research provides a radioecological assessment of surface waters and bottom sediments in the vicinity of conserved and reclaimed uranium mining sites in Northern Kazakhstan. Activities of natural radionuclides were determined, and distribution coefficients, radiological hazard indices, committed effective dose, and ecological contamination indices were calculated to evaluate radionuclide mobility and associated environmental risks. Gross alpha activity increases downstream along the Kutunguz River, while uranium isotope activities exceed background levels by 8–10-fold, indicating ongoing radionuclide migration from the conserved Shantobe uranium deposit. In contrast, the Balkhashin quarry, a closed hydrological system, demonstrates substantial accumulation of ²²⁸Ra attributable to limited water exchange. Distribution coefficient analysis indicates high uranium mobility in flowing river systems and enhanced retention in closed water bodies. Although most radiological hazard indices remain within internationally accepted limits, localized radiological risk is observed in the quarry area. The committed effective dose from drinking water at the background site exceeds the WHO screening level but remains below the ICRP recommended limit. The obtained results indicate differences in the behavior of radionuclides in flowing and closed hydrological systems, as well as the persistent impact of conserved uranium mining facilities on aquatic ecosystems.