Accumulation and discharge kinetics of radionuclide 137Cs by zebrafish

[Objective] Although nuclear energy provides economic benefits, it releases substantial radioactive substances into nearby waters, thereby affecting the ecological environment. Aquatic organisms in radioactive waters accumulate nuclides, reaching a stable concentration within their bodies over time. At this point, the concentration factor, combined with the nuclide concentration in aquatic organisms, can be used to estimate the radioactivity level in target waters. Radiation doses at other trophic levels can be estimated through the food chain. During the transmission process of the food chain, different degrees of radionuclide accumulation were observed at various fish trophic levels. In addition, at the same trophic level, radionuclide accumulation usually differs in fish individuals with various feeding and metabolic rates. Therefore, the concentration factor of different fish species, especially those with large differences in body size, varies considerably. Direct application of the concentration factor recommended by the International Atomic Energy Agency may lead to large deviations in the calculated results. Zebrafish are commonly used aquatic model organisms in the laboratory. This typically small fish has a length of 3—5 cm and is sensitive to changes in the water environment, making it an ideal indicator organism for environmental monitoring. Therefore, this study considered zebrafish as the research subject to explore the accumulation and discharge kinetics of Cs, which is one of the main radionuclides in the liquid effluents of nuclear power plants, to provide a reference for assessing the impact of nuclear power development on aquatic organisms.[Methods] Zebrafish were bred in radioactive water via a specially designed breeding method and equipment, and 137Cs activity in live zebrafish was measured periodically through high-purity germanium gamma spectrometry. The reliability of the living efficiency scale was verified through the gray treatment of zebrafish postmortem.[Results] The results showed a 8. 16% average absolute relative error between measurements obtained from living and deceased zebrafish, which confirmed the scale's reliability. Accumulation and discharge experiments revealed that under approximately 1 000 Bq/L radioactivity, 137Cs after being rapidly accumulated in the zebrafish during the initiation of the experiment and 13/Cs activity in zebrafish increases linearly. Then, after approximately 50 days, the value remained unchanged and reached equilibrium. At the beginning of the discharge experiment, the 13'Cs activity in zebrafish decreased rapidly. However, from around the 60th day, the decreased trend of 137Cs activity became insignificant, and the curve flattened in later stages.[Conclusions] Zebrafish exhibited relatively low 13'Cs accumulation with a concentration factor of (5. 81 +0. 23)L/kg at equilibrium. The 13'Cs discharged by zebrafish exhibited an initial rapid change, followed by a slow rate of change. When all the zebrafish died on the 198 day, the specific activity of 13, Cs remained at approximately 2 370 Bq/kg. This finding suggests the prolonged discharge of Cs in zebrafish, indicating a relatively low metabolic rate and difficult discharge. Zebrafish are sensitive to changes in the water environment, and the accumulation and discharge characteristics of Cs can provide a reference for investigating the influence of liquid effluents from nuclear power plants on other aquatic organisms and assessing the water environment. © 2024 Tsinghua University. All rights reserved.