Clay-Mediated Phototransformation Alters the Molecular Composition and Toxicity of Microplastic-Derived Dissolved Organic Matter

Our study showed that montmorillonite (Mt) accelerated the photodegradation of PS and PLA microplastics, increasing the maximum release of MPs-DOM by 50.3% and 27.6%, respectively, while shifting its composition toward greater molecular complexity, fluorescence intensity, and aromaticity.

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that Mt altered the distribution of extractable molecular formulas, increasing the relative contribution of features within more unsaturated and oxygenated compositional regions. Quantitative analysis of reactive oxygen species (ROS) showed that the synergistic interaction between MPs-DOM and Mt influenced ROS production. Specifically, Mt increased [•OH]_ss in PS- and PLA-DOM by 136.8% and 88.7%, respectively, but decreased [¹O₂]_ss by 32.7% and 13.6%, respectively, indicating that •OH was an important contributor to molecular transformation.