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Spatial heterogeneity of EPS-mediated microplastic aggregation in phycosphere shapes polymer-specific Trojan horse effects
Summary
Researchers investigated how algal communities in water aggregate different types of microplastics through sticky extracellular substances they produce. They found that the binding behavior varied significantly by plastic type and by the layer of the algal colony, with some plastics being captured more effectively than others. The study reveals that these natural aggregation processes can concentrate pollutants on microplastic surfaces, creating a "Trojan horse" effect that increases risks to organisms that consume the clumps.
The pervasive contamination of aquatic ecosystems by microplastics represented a critical environmental challenge. While algal-bacterial symbiosis systems demonstrated potential for microplastic aggregation via extracellular polymeric substances (EPS), prior studies have focused on temporal dynamics rather than spatial heterogeneity in phycosphere. This study systematically investigated the adsorption mechanisms of Polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene (PE) and polystyrene (PS) across stratified EPS fractions, tightly bound (TB-EPS), loosely bound (LB-EPS), and soluble (S-EPS), in phycosphere. Combining controlled aggregation assays with multimodal characterization, we revealed a hierarchical spatial framework governing EPS-microplastic interactions. Adsorption efficiency governed by polymer-specific interfacial energies and EPS organic composition. EPS at distinct hierarchical levels exhibited material-specific adsorption preferences for microplastics. PVC and PET demonstrated higher affinities for hydrocarbon components, while PE and PS were preferentially captured through interactions with polysaccharides and amide I groups, respectively. The adsorption and aggregation behaviors between EPS and microplastics in the phycosphere promoted eco-corona formation and induced the Trojan horse effect. However, the energy barrier of interaction forces and EPS spatial configurations jointly governed the hierarchical stabilization of polymer-specific microplastics. PVC and PET primarily colonized the outermost S-EPS layer, PS preferentially accumulated in the intermediate LB-EPS layer, and PE penetrated into the innermost TB-EPS layer. These findings addressed a key knowledge gap by delineating the ecological niche-specific distribution of EPS-microplastic binding, offering novel insights for optimizing bioremediation strategies and informing regulatory measures targeting particulate plastic pollution in hydrologic systems.