Eco-corona formation on aminated nanoplastics interacted with extracellular polymeric substances from bloom-forming cyanobacteria: Insightful mechanisms with DFT study

Nanoplastics (NPs) with amino functional groups have wide distribution and high toxicity; however, their environmental behaviors remain inadequately understood. This study investigated the mechanisms of eco-corona formation on pristine polystyrene NPs (PSNPs) and aminated PSNPs (PSNPs-NH2) by extracellular polymeric substances (EPS) from a bloom-forming cyanobacterium, Microcystis aeruginosa. Our results revealed that at the two tested concentrations of EPS (5.0 and 30.0 mg/L), the pristine PSNPs initially aggregated and subsequently repelled. In contrast, PSNPs-NH2 showed a more pronounced aggregation at the elevated EPS concentration of 30 mg/L. In addition, the elemental compositions and functional groups on both types of PSNPs were markedly altered after eco-corona formation. Combining with density functional theory, our findings indicated that electrostatic interaction, hydrogen bonding, and Van der Waals force served as the main binding forces between model EPS (polysaccharide) and PSNPs units. Furthermore, the binding energies of pristine PSNPs-, and PSNPs-NH2-polysaccharide were calculated to be -63.25 and -179.43 kJ/mol, respectively, suggesting a greater affinity of PSNPs-NH2 for polysaccharide. This outcome aligned with our experimental observation. Specifically, the xylose branch within polysaccharide was identified as an optimized binding site for interaction with PSNPs. Our research contributes to a deeper understanding of the environmental behaviors of aminated NPs in freshwater systems, particularly during periods of cyanobacterial blooms.