By comparing five common polymers under ozone- and ultraviolet-aging conditions, the study found that weathering can either strengthen or weaken adsorption depending on the plastic and organic matter type. These findings provide a more detailed basis for predicting how microplastics move, transform, and interact with coexisting pollutants in aquatic environments.
Microplastics are now widely detected in rivers, lakes, oceans, sediments, and engineered water systems. In natural waters, they are rapidly coated by dissolved organic matter, forming an “eco-corona” that can change their surface charge, hydrophobicity, colloidal stability, mobility, and contaminant-carrying capacity. Previous studies have documented that dissolved organic matter can adsorb onto microplastics, but most have focused on bulk adsorption rather than selective fractionation. Because dissolved organic matter contains diverse humic-like, fulvic-like, aromatic, hydrophilic, and molecular-weight fractions, it remains difficult to predict which components will attach to different weathered plastics. These uncertainties call for deeper investigation into how microplastic properties and environmental aging jointly regulate dissolved organic matter fractionation.
A study (DOI: 10.48130/ebp-0026-0004) published in Environmental and Biogeochemical Processes on 30 March 2026 by Tianchi Cao’s team, Nankai University, reports that dissolved organic matter adsorption is governed by the combined effects of polymer chemistry, oxidative aging, and organic matter composition.
The researchers selected five representative microplastics: polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyvinyl chloride (PVC). The plastics were exposed to controlled ozone (O₃) and ultraviolet (UV) aging to simulate oxidative weathering pathways relevant to aquatic environments. Suwannee River fulvic acid (SRFA) and Suwannee River humic acid (SRHA) were used as model dissolved organic matter because they differ in aromaticity, molecular weight, and functional groups. The team then combined adsorption isotherm experiments, dissolved organic carbon measurements, fluorescence excitation–emission matrix analysis with parallel factor analysis, molecular-weight fractionation, surface characterization, and machine-learning-assisted modeling. The results showed that pristine plastics behaved differently depending on the organic matter type. SRFA showed broadly similar distribution coefficients across pristine polymers, whereas SRHA displayed strong polymer-dependent variation. On aromatic or more polar polymers such as PS, PET, and PVC, SRHA generally showed higher adsorption affinity than SRFA, likely because its stronger aromatic character favored hydrophobic and π–π interactions. Aging further complicated this pattern. For example, O₃-aging increased SRFA adsorption on PE, while aging reduced SRFA adsorption on PET, PVC, and some PS samples. For SRHA, aging reduced adsorption on PE, PS, and PVC but enhanced adsorption on PET. Fluorescence and molecular-weight analyses showed that aging also changed which dissolved organic matter fractions were retained. Aged PE and PP tended to enrich low-molecular-weight, more hydrophilic SRFA fractions, while aged PET favored larger and more aromatic SRHA components. Machine-learning analysis identified specific surface area and surface carbon speciation as the leading predictors of adsorption behavior, indicating that both physical sorption capacity and interfacial chemistry are essential controls.
Overall, the study demonstrates that dissolved organic matter fractionation on microplastics cannot be generalized by polymer type or aging state alone. Instead, adsorption reflects a balance between weathering-induced increases in surface area and porosity, which can create new sorption sites, and increased surface oxygenation, which can reduce hydrophobic interactions. By linking measurable surface features to selective organic matter adsorption, the work offers a mechanistic framework for improving models of microplastic transport, stability, contaminant interactions, and ecological risk in real aquatic systems.
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References
DOI
10.48130/ebp-0026-0004
Original Source URL
https://doi.org/10.48130/ebp-0026-0004
Funding Information
This work was supported by the National Natural Science Foundation of China (Grant Nos 22241602 and 22020102004) and Tianjin Municipal Science and Technology Bureau (Grant Nos 23JCYBJC01650 and 23JCQNJC01340). This work was also supported by the Austrian Science Fund, Cluster of Excellence COE7 (Grant DOI 10.55776/COE7 [Thilo Hofmann]).
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