Effects of gadolinium on oxidative stress and oxidative DNA damage in zebrafish ( Danio rerio ) at different temperatures

Rare earth elements (REEs) are widely used in high-tech applications across industries such as electrical and electronics, automotive, renewable energy, medical and defense. Consequently, lobal demand for REEs is increasing, driven by developing economies, green technology, and R&D. As their usage grows, REE waste discharged into the environment accumulates and pollutes aquatic ecosystems. Climate change-induced temperature increases are known to adversely affect the vital functions of organisms. It is hypothesized that the impact of environmental pollutants is exacerbated by rising temperatures. This study aimed to investigate the effects of Gadolinium (Gd), selected as a representative REE, at concentrations of 0 (control), 10, 50, and 250 mg/L on the model organism Danio rerio under different temperature conditions (22, 27, and 32 °C), using biochemical biomarkers and an oxidative DNA damage biomarker. Superoxide dismutase (SOD) and catalase (CAT) levels, glutathione peroxidase (GPx) activity, as well as malondialdehit (MDA) and reduced glutathione (GSH) levels, were measured in whole-body tissue supernatants at 24 and 96 h. Additionally, oxidative DNA damage was evaluated using 8-hydroxy-2′-deoxyguanosine (8-OHdG). Results showed decreased SOD and CAT levels, decreased GPx activity, increased MDA levels, decreased GSH levels, and increased 8-OHdG levels. These findings indicate alterations in antioxidant defense, lipid peroxidation, and oxidative DNA damage following Gd exposure under the tested temperature conditions.