Bioaccumulation of 40K in different fish species of river ecosystems of Zhytomyr Polissia

The article presents the results of a comprehensive study of bioaccumulation of the natural radionuclide 40K in tissues of four commercial fish species (silver carp Hypophthalmichthys molitrix, common carp Cyprinus carpio, crucian carp Carassius auratus, pike Esox lucius) caught in the Zdvyzh River of Zhytomyr region in January 2025.A comparative analysis of 40K concentration in different anatomical parts of fish – edible part (muscle tissue) and head with internal organs – was conducted. Measurement of specific activity of 40K was performed by gamma spectrometry using certified equipment according to international standards. It was established that the highest indicators of specific activity of 40K were recorded in predatory fish species – pike (156.00 Bq/kg in muscle tissue and 113.00 Bq/kg in head with internal organs), while in herbivorous and omnivorous species (silver carp, common carp) these indicators were significantly lower (85.80 and 62.90 Bq/kg in muscle tissue, respectively). A pattern of 0K concentration predominantly in muscle tissue compared to the head and internal organs was revealed for all studied fish species, which differs from the distribution pattern of technogenic radionuclides. The greatest difference in concentration between anatomical body parts was recorded in pike (38.1 %) and silver carp (43.5 %), while for common carp and crucian carp this difference was 17.1 % and 18.8 %, respectively. It has been demonstrated that, unlike technogenic radionuclides (137Cs, 90Sr), which typically accumulate in bone tissue and internal organs, 40K as a physiologically active element concentrates mainly in muscle tissue. Statistical analysis of the data confirms the species specificity of 40K accumulation, which is related to trophic specialization and metabolic characteristics of different fish species. The recorded levels of 40K content are within the regional background values for water bodies of Ukrainian Polissia. The obtained results are important for assessing the radioecological state of aquatic ecosystems in the long term after the Chornobyl accident and can be used for monitoring the quality of aquaticbioresources and developing recommendations for their safe use.