Epigenetic and genotoxic effects of tritium in marine mussels: Comparing waterborne and metal-associated forms

Tritium (³H), an isotope of hydrogen, is a by-product of the nuclear industry. Decommissioning and normal operations of nuclear facilities can generate tritiated stainless-steel particles (T-SSPs) that could be unintentionally released into the environment. Considering tritium's physicochemical properties and the proximity of nuclear facilities to water bodies, assessing the behaviour and potential effects of these particles in the aquatic environment is imperative. In the present study, marine mussels, Mytilus galloprovincialis, were exposed to: (a) hydrogenated, non-radioactive stainless-steel particles (H-SSPs) (10 mg L^-1) (b) T-SSPs (1 and 10 MBq L^-1) and (c) tritiated water (HTO) (0.50 and 5.0 MBq L^-1) for 5 h and 7 d. Exposure to T-SSPs resulted in significant DNA damage in mussel haemocytes. Tritium bioaccumulation was significantly higher in the digestive gland (DG), regardless of the exposure duration to T-SSPs. Positive correlation between tritium in DG tissues and DNA indicates that tritium is internalised in the cell. After 7 d, global DNA methylation increased in gills exposed to both 1 MBq L^-1 of T-SSPs and 5 MBq L^-1 of HTO treatments. In the DG tissue, DNA methylation increased following exposure to tritium (water and particulate forms) compared to H-SSPs, suggesting a tissue-specific and pollutant-dependent response. Our findings highlight the enhanced bioaccumulation of T-SSPs compared to HTO. Multivariate analyses of the results suggested an overall stress response in mussels exposed to T-SSPs compared to HTO exposure and controls. Potential epigenetic effects will require more attention as they can bring knowledge across levels of biological organisation and about the transgenerational impact of radionuclides.