Pyridaben-induced biochemical and molecular stress in Daphnia magna

Pyridaben (PDB) is a widely used acaricide in agriculture, classified as highly toxic to aquatic life (H400, H410; USEPA) because it inhibits mitochondrial complex I. This study aimed to evaluate the subacute toxicity of PDB (0.20-0.80 TU for 48 h) in the model organism Daphnia magna using an integrated molecular and biochemical multi-biomarker approach. To the best of our knowledge, this is the first comprehensive study to integrate molecular and biochemical markers related to oxidative stress and osmoregulation in assessing subacute PDB toxicity in D. magna using the Integrated Biomarker Response index (IBR). PDB exposure altered antioxidant system dynamics, with decreased SOD and GPX activities, increased CAT and GST activities, and elevated GSH and TBARS levels. The increase in Ca²⁺-ATPase activity was positively correlated with antioxidant enzymes, suggesting an adaptive osmoregulatory response to oxidative stress. Reduced total protein levels were negatively correlated with most of the biomarkers. At the molecular level, while the expression of oxidative stress-related genes decreased, miR-153 was significantly upregulated, showing a negative correlation with these genes but a positive correlation with other biomarker levels. The results revealed significant and interrelated alterations at both biochemical and molecular levels, and IBR analysis demonstrated that responses were notably triggered at 0.35 TU, with maximal effects observed at concentrations of 0.50 TU and above. These findings provide new insights into the ecological risk of PDB, supporting the use of multi-biomarker approaches for environmental monitoring, as well as elucidating molecular pathways underlying the adaptive responses of aquatic organisms to stress.