Radionuclide contamination of rivers in Zhytomyr Polissia: analysis of bioaccumulation in hydrobionts

The objective of this study was to conduct a comprehensive radioecological assessment of aquatic ecosystems in Zhytomyr Polissia during the remote period following the Chornobyl Nuclear Power Plant accident, with detailed determination of radionuclide contamination levels in bottom sediments, water, and commercial fish species, as well as analysis of bioaccumulation patterns of radiocesium and radiostrontium in hydrobionts. The research was conducted in January 2025 on water bodies within the Teteriv River basin in Zhytomyr Oblast using modern radiochemical and gamma-spectrometric analytical methods. Samples of bottom sediments from depths of 0.5-1.0 m, surface layer coastal sediments (0-5 cm), and water from the Teteriv River within Zhytomyr city were collected and analyzed, along with samples of muscle tissue and the “head + internal organs” complex from four commercial fish species (silver carp, common carp, Prussian carp, northern pike) from the Zdvyzh River in Brusyliv district. Determination of specific activity of radionuclides 137Cs, 90Sr, and natural 40K was performed in the accredited measurement laboratory of Polissia National University with measurement error not exceeding 15-20% at a confidence probability of 0.95. Significant differentiation of radionuclide concentrations between different components of the aquatic ecosystem was established. The highest concentrations of 137Cs are observed in bottom sediments (25.81 Bq/kg) and coastal sediments (20.26 Bq/kg), which is 71.7 times higher than water indicators (0.36 Bq/kg). Concentrations of 90Sr are characterized by the opposite pattern with maximum values in coastal sediments (8.60 Bq/kg) due to the higher mobility of this radionuclide. Among the studied fish species, the highest 137Cs content was recorded in cyprinid species: carp (3.16-5.45 Bq/kg), silver carp (2.51-4.76 Bq/kg), and the lowest in pike (1.53-3.17 Bq/kg) and Prussian carp (0.95-2.05 Bq/kg). Concentrations of 90Sr in fish tissues ranged from 12.90 Bq/kg in pike to 26.30 Bq/kg in silver carp, which is 2-4 times higher than background values for the region. The identified species-specific bioaccumulation of radionuclides is related to the peculiarities of feeding behavior, ecology, and physiology of the studied species. Concentrations of 137Cs and 90Sr in fish muscle tissue do not exceed current hygienic standards for food products; however, elevated levels in internal organs require their mandatory removal during processing. Concentrations of the natural radionuclide 40K in bottom sediments and fish tissues correspond to literature values for the region. The results demonstrate the necessity of continuing systematic radioecological monitoring of aquatic bioresources in the region and developing scientifically based measures to minimize radioecological risks to ensure safe utilization of aquatic ecosystems in Zhytomyr Polissia