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Clay-Mediated Phototransformation Alters the Molecular Composition and Toxicity of Microplastic-Derived Dissolved Organic Matter
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In lab experiments, a clay mineral called montmorillonite sped up sunlight-driven breakdown of two microplastics (PS and PLA), releasing more dissolved organic matter with more complex chemical makeup. This clay-altered matter produced different reactive oxygen species and showed greater effects on bacteria than microplastic breakdown products formed without the clay.
Abstract Microplastics (MPs) release complex dissolved organic matter (MPs-DOM) during environmental weathering, yet how clay minerals regulate MPs-DOM release, molecular composition, and associated biological effects remains unclear. 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. The Mt-amended MPs-DOM exhibited a broader profile of detectable additive-related candidates and induced greater bacterial effects than Mt-free systems. These findings demonstrate that clay minerals critically regulate the environmental fate of MPs-DOM by modulating radical generation, potentially amplifying the persistence and risks of MP pollution.
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