Identification of persistent substructures in transformation products with zebrafish embryos using cheminformatics...

Substances transform in environmental and biological matrices to produce diverse transformation products (TPs). Some chemical moieties, termed persistent substructures, are retained in these TPs. This study used literature TPs, literature-derived analogous TPs (i.e., TPs inferred by applying literature-reported transformations from structurally similar precursors) and predicted TPs to identify known and novel TPs of five selected data-poor compounds using zebrafish embryos. The workflow was then used to identify persistent substructures in a further 36 persistent, mobile and toxic (PMT) compounds from the triazine, triazole and PFAS classes. The suspect screening workflow in patRoon was applied to liquid chromatography high-resolution mass spectrometry data. This study identified 91 TPs at confidence levels 1 (confirmed) or 3 (tentative): 34 from data-poor parents and 57 from the PMT compounds, including 13 Level 1s. Among data-poor compounds, 17 TPs (52%) were analogous TPs, whereas 17% were exclusively predicted. Among PMT compounds, most TPs (63%) were predicted exclusively using BioTransformer, while 12.3% were solely literature TPs. The combined approach yielded a better TP coverage compared to any single source, revealing extensive biotransformation even for PMT substances - indicating that persistence does not exclude downstream transformation. The transformations included phase I and II metabolic reactions, as well as non-enzymatic processes. The 1,3,5-triazine ring, benzotriazole ring and CF₃ group were conserved in all TPs of their respective parent compounds, while the 1,2,4-triazole ring was found in most, but not all, triazole TPs. QSAR modelling predictions indicated that several TPs were potentially more persistent, mobile and toxic than their parents. The study shows the significance of including the concept of persistent TP substructures in chemical risk assessments.