Evaluating the behavior and environmental risks of carbamazepine and its metabolites in soil aquifer treatment: Insights from deconjugation dynamics and toxicity assessment

The presence of pharmaceuticals in the environment has been a growing concern. Recent studies highlight the ecological risks of pharmaceuticals, but most risk assessments focus on the parent drug, neglecting metabolites. This study examines the behavior and environmental risks of carbamazepine (CBZ) and its metabolites in soil aquifer treatment (SAT) for wastewater reclamation. Findings indicate that CBZ metabolites' total concentration exceeds that of CBZ. Notably, carbamazepine-N-glucuronide (CBZ-N-Glu) concentration decreased from 48.12 ng/L to undetectable levels during SAT, while CBZ concentration increased from 64.87 to 95 ng/L, suggesting possible deconjugation of CBZ-N-Glu. Batch and column experiments confirmed the hypothesis, showing a gradual disappearance of CBZ-Glu and a corresponding rise in CBZ concentration when CBZ-N-Glu was spiked into a recirculated SAT system. Quantitative structure-activity relationships (QSAR) analysis revealed that CBZ exhibits higher acute and chronic toxicity, with metabolites showing varying levels of developmental toxicity. The study also evaluates the persistence, mobility, and toxicity (PMT) characteristics of CBZ and its metabolites, highlighting CBZ-N-Glu's particularly adverse PMT characteristics compared to CBZ. In summary, the residual pharmaceuticals in the reclaimed water process should be evaluated systematically, considering both the parent compounds and their metabolites.