Liver toxicity in Nile tilapia fish exposed to lithium: oxidative lipidomics and histopathological features.

Lithium (Li) has emerged as a significant environmental pollutant due to its increasing use in electric vehicle batteries, renewable energy storage, and electronics. This study aimed to assess the potential toxic effects of Li exposure (5, 10, and 25 mg/L of Li) over 48 h on lipid peroxidation, fatty acid composition (FA), oxidative status and histopathological alterations in the liver tissue of Oreochromis niloticus (Nile tilapia). Li exposure triggered oxidative stress in the liver of Nile tilapia fish, as demonstrated by increased levels of hydrogen peroxide (H₂O₂), lipid hydroperoxides (LOOH), and malondialdehyde (MDA). This was accompanied by significant biochemical alterations, including elevated activities of superoxide dismutase (SOD) and glutathione-S-transferase (GST), alongside a reduction in reduced glutathione (GSH) levels. Furthermore, exposure to Li led to increased glutathione peroxidase (GPx) activity and protein carbonyl (PCO) content, reflecting intensified oxidative damage and protein oxidation. A significant reduction in saturated fatty acids (SFA) was observed, coupled with an increase in polyunsaturated fatty acids (PUFA) in all Li-treated fish. Notably, there was a substantial rise in n-3 PUFA levels, particularly eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3), which correlated with increased activity of Δ4 and Δ5 desaturases. Additionally, levels of n-6 PUFAs, especially arachidonic acid (ARA, C20:4n-6) and its precursor linoleic acid (LA, C18:2n-6), were significantly elevated. Histopathological examination revealed significant tissue damage and abnormalities in the liver, further confirming the biochemical changes observed. These findings suggest that O. niloticus can adapt to Li-induced stress by modulating its lipid metabolism to maintain membrane integrity. This study provides new insights into the mechanisms of Li toxicity and highlights the fatty acid profile as a sensitive and valuable biomarker for environmental risk assessment in aquatic ecosystems.