Comprehensive Assessment of Natural Radionuclides in Commercial Fish Feed: Radiological Risk, Food Chain Implications, and Public Health Perspectives

Fish feed can serve as a pathway for radionuclides to enter aquatic food chains, posing potential health risks to both fish and humans. This study investigated the levels of naturally occurring radionuclides—potassium-40 ( 40 K), radium-226 ( 226 Ra), and thorium-232 ( 232 Th)—in fifteen commercial fish feed samples collected from regional markets. Samples were prepared by drying, grinding, and sieving, followed by sealing for 28–30 days to achieve secular equilibrium. Radionuclide activity was measured using high-purity germanium (HPGe) gamma spectrometry with appropriate energy and efficiency calibration. Results revealed that 40 K exhibited the highest activity (range: 98.11–610.87 Bq/kg; mean: 312.3 Bq/kg), followed by 226 Ra (4.32–15.00 Bq/kg; mean: 9.57 Bq/kg) and 232 Th (3.21–11.20 Bq/kg; mean: 7.59 Bq/kg). Statistical analyses indicated moderate variability in 40 K and more uniform distribution for 226 Ra and 232 Th, with a moderate positive correlation between 40 K and 232 Th (r = 0.62). The committed effective dose (CED) for adult consumers, calculated based on radionuclide activity and standard dose conversion factors, remained below the recommended public limit of 1 mSv/year. The findings suggest that, although radionuclide concentrations vary across feed brands, the overall radiological risk from consuming fish fed with these products is within safe limits. This study provides essential baseline data for monitoring radionuclide contamination in aquaculture feeds and highlights the importance of continuous assessment to ensure food safety and public health.