Retrospective non-target screening reveals the occurrence and environmental risk of pharmaceutical transformation products in the Pearl River Basin.

Pharmaceutical transformation products (TPs) can pose greater environmental risks than parent compounds, yet their occurrence in surface waters remains inadequately characterized. This study employed retrospective analysis of non-target screening (NTS) data, literature mining, and molecular networking to characterize pharmaceutical TPs in the Pearl River Basin (PRB). Suspect screening against TP databases identified 74 TPs, while molecular networking revealed 62,387 feature pairs sharing common MS/MS fragments. Structural annotation suggested 51 TPs derived from 28 parent pharmaceuticals, including 26 previously unreported compounds. Hydroxylation, methylation, demethylation, and oxidation were the dominant transformation pathways, showing minimal sub-basin variation-indicating structural control over transformation processes. Predictive assessment revealed 65% of TPs exhibited enhanced mobility and 23% showed increased toxicity relative to parent compounds. Notably, the TP SR-49498 showed a significantly higher environmental risk quotient (RQ = 13.271) than its parent Irbesartan (RQ < 0.0001). Toxicological Priority Index (ToxPi) analysis prioritized 12 high-risk TPs. Overall, this study systematically characterized the occurrence and environmental risks of pharmaceutical TPs in the PRB, thereby advancing the understanding of their environmental fate and providing a scientific basis for future water pollution monitoring and risk management strategies.