What lies beneath the ice? How gadolinium affects Cyclops abyssorum during Alpine winters.

The increasing anthropogenic release of gadolinium (Gd) from medical contrast agents raises concern regarding its fate and ecotoxicological effects in freshwater ecosystems. Gd may reach alpine lakes through atmospheric deposition, entering environments already fragile due to extreme conditions. This study examined the sublethal effects of Gd on the alpine copepod Cyclops abyssorum under simulated winter conditions (4 °C, darkness). Organisms were exposed for 14 days to 1-150 µg/L Gd, and oxidative stress biomarkers were measured. Glutathione peroxidase activity increased with concentration, while malondialdehyde indicated lipid peroxidation. Superoxide dismutase and glutathione S-transferase showed non-linear responses, suggesting physiological thresholds or enzyme inhibition. The Threshold-based Integrative Biomarker Response (IBR-T) index revealed progressively higher stress at intermediate and high exposures. Overall, the results indicate that Gd can induce oxidative stress in cold-adapted zooplankton, emphasizing the importance of assessing contaminant risks in alpine lakes using non-model species and realistic exposure scenarios.