Advanced Computational Approaches for Unraveling Transformation Pathways of Organic Micropollutants in Aquatic Environments: Insights from the Photodegradation of Ciprofloxacin.

Investigating the transformation products (TPs) of organic micropollutants in aquatic environments is crucial for understanding their fate, evaluating ecological and human health risks, and developing effective mitigation strategies to protect water quality. Thus, it is essential to establish an efficient workflow with low technical complexity for high-throughput TP identification. In this study, high resolution mass spectrometry (HRMS), stable isotope-labeled compounds, and similarity analysis were combined to develop an advanced computational approach for investigating the phototransformation processes of ciprofloxacin. A total of 68 tentatively ciprofloxacin-related TPs were extracted through isotope labeling experiments and formula filtering. Furthermore, structural elucidation of 42 TPs was achieved by combining HRMS/MS fragments and stable isotope labeling results, revealing that piperazinyl and cyclopropyl moieties are the key reaction sites of ciprofloxacin under solar irradiation. A novel similarity analysis workflow was developed to map the phototransformation pathways, establishing 80 parent-TP pairings. Dealkylation, oxygen addition, decarboxylation, and defluorination were found to be the dominant phototransformation reaction types of ciprofloxacin. The study highlights the complexity of ciprofloxacin phototransformation and provides a robust computational framework for elucidating the degradation pathways of organic contaminants. The developed methodology can be extended to study other emerging contaminants, supporting the design of more effective water treatment strategies and comprehensive risk assessments.