Genotoxic Effects in Spleen and Bone Marrow of Wistar Rats Chronically Exposed to Tritium Oxide and 3H-Thymidine with Drinking Water

Purpose: The operation of nuclear facilities such as NPPs is accompanied by the formation and release of tritium compounds into the environment. Currently available data on the biological effects of tritium, especially its organic compounds, are very scattered and fragmentary. There is still no consensus on the regulation of the content of inorganic and organic tritium compounds in different environments. This leads, for example, to a wide range of permissible levels of tritium in the environment in different countries, which requires additional experimental and calculated data in order to harmonize standards and ensure the safety of the members of the public living near such nuclear facilities. The purpose of this work is a comparative assessment of molecular cellular biological effects (formation of DNA double-strand breaks and micronuclei) upon exposure to individual tritiated compounds in mammals. Material and methods: An in vivo study was conducted on male rats that received orally drinking water containing tritium oxide (HTO) or 3H-thymidine with a volumetric specific activity of 800 kBq/l for 10, 21 and 31 days. The number of DNA double-strand break (DSB) repair foci in rat splenocytes was assessed by immunocytochemical staining of phosphorylated histone H2AX (γH2AX) foci. An analysis of the frequencies of polychromatophilic erythrocytes (PCE) with micronuclei (MN) in the bone marrow of rats was also carried out. Results: The genotoxic effect of both forms of tritium was determined by a significant yield of DNA DSBs in splenocytes and micronuclei in bone marrow PCE (a more pronounced effect on the 31st day of 3H-thymidine action). With chronic exposure to 3H-thymidine on days 21 and 31, the number of γH2AX foci significantly increases; in the case of HTO, the level of foci on days 31 does not significantly change. Exposure to HTO and 3H-thymidine caused approximately the same induction of PCE with micronuclei on days 10 and 21, but by day 31 the effect of 3H-thymidine was approximately 40 % greater than that of HTO. The experiment revealed a likely genotoxic effect of inhaled tritium in control rats that were kept in the same room as the rats that received HTO and 3H-thymidine orally. However, additional experiments are needed to confirm this effect. Conclusion: The result of this work expands the understanding of the mutation process in mammalian cells exposed to internal ionizing radiation when taking compounds containing tritium. Increased genotoxicity is observed when rats ingest drinking water containing tritium with an activity of 800 kBq/l.