Oxidative Stress Responses and Antioxidant Gene Regulation in Daphnia pulex Following Chronic Benzyl Alcohol Exposure

Benzyl alcohol was evaluated for its short-term and long-term toxicity in Daphnia pulex, with an emphasis on oxidative stress biomarkers and antioxidant-related gene expression. Acute toxicity was evaluated over 48 h to estimate the LC50, and two sublethal concentrations (11.5 and 23 mg/L) were subsequently selected for a 21-day exposure. Activities of catalase (CAT), superoxide dismutase (SOD), and glutathione S-transferase (GST), and the expression profiles of cat and sod were measured, and associations between biochemical and molecular responses were examined. Mortality increased with concentration, yielding a 48 h LC₅₀ of 229.68 mg/L. Prolonged exposure produced contrasting responses moderate stress stimulated antioxidant enzymes and gene expression, whereas higher exposure suppressed enzymatic activity, depleted glutathione reserves, and reduced transcriptional responses. Enzyme activities were positively correlated with gene expression, indicating coordinated regulation of the antioxidant defense system. These patterns indicate that oxidative imbalance develops at concentrations well below lethal thresholds and precedes overt mortality, supporting the use of biochemical and molecular biomarkers as sensitive indicators of chronic toxic stress in freshwater invertebrates.