Combination of microplastics-derived DOM with natural humic/fulvic acids accelerates atorvastatin photodegradation in freshwater environments.

Microplastics-derived dissolved organic matter (MPs-DOM) in aquatic environments inevitably interacts with natural organic matter (NOM), yet their interaction kinetics and underlying mechanisms remain underexplored. Herein, we investigated the combination of DOM derived from polypropylene (PP) and polylactic acid (PLA) MPs with NOM (Suwanee River humic acid (SRHA) and Suwanee River fulvic acid (SRFA)) in freshwater systems. Results demonstrated that under UV irradiation, MPs-DOM derived from PP and PLA MPs could combine with coexisting SRHA/SRFA in water, forming MPs-DOM-SRHA and MPs-DOM-SRFA complexes. Notably, these complexes exhibited a differential structural composition and higher molecular weight compared to individual PP-DOM and PLA-DOM, particularly in the range of 10³ to 10⁴ Da. In addition, compared with the sole SRHA and SRFA, the MPs-DOM-SRHA/SRFA complexes significantly accelerated the photo transformation of atorvastatin (ATV). This phenomenon is attributed to the presence of highly unsaturated and phenolic compounds in MPs-DOM-SRHA/SRFA, which generated more oxidatively reactive oxygen species (ROS)-including hydroxyl radicals (•OH), superoxide anions (O₂•⁻), and singlet oxygen (¹O₂)-than SRHA and SRFA alone, thereby enhancing the photodegradation of ATV in water. These findings highlight that MPs-DOM-SRHA/SRFA complexes possess a distinct structural composition compared to individual MPs-DOM or natural organic matter (NOM), and may exhibit uncharacterized environmental behaviors and ecological risks in aquatic ecosystems.