When antioxidant defences collapse: Gen-X induced oxidative stress in Procambarus clarkii hepatopancreas and gills.

Gen-X (ammonium salt of hexafluoropropylene oxide dimer acid) was introduced as a safer alternative following restrictions on perfluorooctanoic acid. Although its short-chain structure reduces its bioaccumulation potential, research suggests it may mimic some toxic effects of legacy perfluoroalkyl substances. Its persistence and high mobility in freshwater ecosystems amplify concerns about impacts on biota. This study investigates whether sub-chronic Gen-X exposure can induce oxidative stress, leading to cellular damage and antioxidant responses in the hepatopancreas and gills of Procambarus clarkii, a resilient, invasive crayfish. Individuals were maintained for 28 days in four experimental tanks: three Gen-X doses (0.5, 1, 10 µg/L) and one control. Chemical analyses revealed dose-dependent accumulation in tissues, mostly in the hepatopancreas. Oxidative biomarkers showed evidence of cellular damage, including early lipid peroxidation in the hepatopancreas at 1 µg/L and protein and lipid oxidation in both organs at the highest concentration. Enzymatic assays revealed tissue-specific responses. In the hepatopancreas, superoxide dismutases (SODs) activity was inhibited at the two highest doses, suggesting enzyme impairment, while it was activated in gills. In both organs, Se-dependent glutathione peroxidases (Se-GPxs) exhibited a biphasic response, with activation at low exposure and collapse at higher doses, coinciding with macromolecular injury. Catalase was alternatively inhibited at 0.5 µg/L in the hepatopancreas and activated at 1 µg/L in gills, indicating compartment-specific detoxification. These results demonstrate that Gen-X disrupts redox homeostasis in P. clarkii through organ-specific accumulation and differential antioxidant modulation, with enzyme inhibition marking critical thresholds beyond which antioxidant defences fail and oxidative damage becomes irreversible.