Molecular transformation of synthetic cannabinoids in surface water

Synthetic cannabinoids (SCs) emerging psychoactive substances increasingly detected in aquatic environments, though their occurrence is often limited by low environmental concentrations and rapid in situ transformation. In this study, EDMB-PINACA was selected as a representative SC to investigate its phototransformation behavior in pure and lake water. The results showed that EDMB-PINACA underwent rapid photodegradation with a half-life of 2.33 days under natural sunlight. Under simulated sunlight, a total of ten phototransformation intermediates were identified using liquid chromatography coupled with Q-Exactive Orbitrap high-resolution mass spectrometry. Electron paramagnetic resonance analysis confirmed the generation of hydroxyl radicals and superoxide anion radicals during irradiation, which contributed to the degradation process. Fukui function analysis identified the pyrazole ring, intraring C–N bond, and amide nitrogen as the primary reactive sites, supporting the proposed transformation pathways. Consequently, ester hydrolysis, N-dealkylation, desaturation, ketone formation, hydroxylation, and dihydroxylation were identified as dominant transformation pathways. Structurally related SCs, including ADB-BUTINACA and MDMB-4en-PINACA, exhibited similar photochemical behaviors and bond-cleavage patterns, indicating the broader applicability of the proposed transformation framework. These findings provide systematic insights into the photochemical fate of EDMB-PINACA and support the inclusion of transformation products in environmental monitoring and risk assessment of SCs in aquatic systems.