Interaction of nanoplastics with extracellular polymeric substances (EPS) in the aquatic environment: A special reference to eco-corona formation and associated impacts

Nanoplastics (NPs) are plastic particles with sizes ranging between 1 and 1000 nm, exhibiting exceptional qualities such as large surface area, lightweight, durability; therefore, are widely used in cosmetics, paints, electronics, etc. NPs are inevitability released into the aquatic environment where they tend to interact with both, the extracellular polymeric substances (EPS) and other fractions of natural organic matter (NOM), respectively secreted by organisms (e.g., DNA, proteins, and carbohydrates) and degradation byproducts of organic materials (e.g., humic acid and fulvic acid) fluxed into the water bodies. These biomolecules robustly encapsulate NPs to develop an eco-corona layer that alters not only the physicochemical properties but also the fate, bioreactivity, and ecological impacts of NPs. Therefore, this review summarized the documented studies highlighting the eco-corona formation on NPs and associated ecological implications in the aquatic environment. After presenting the precise background information on the occurrence of NPs and EPS in the aquatic environment, we demonstrated the basic difference between eco-corona and bio-corona formation. The reviewed studies showed that the eco-corona formed on NPs have varying sizes and composition, mainly depending on the properties of parent biomolecules, characteristics of NPs, and physicochemical parameters of the aquatic environment. Further, the potential methods for characterization and quantification of eco-corona and its composition have been also highlighted. Moreover, the ecological implications (both toxic and non-toxic) of eco-corona formation on NPs in marine and freshwater environments have been also summarized. Last but not the least, challenges and future research directions are also given, e.g., conducting field studies on eco-corona formation in the aquatic environment, optimizing methods for its characterization and quantification, and considering eco-corona concept in the future toxicity studies on NPs. Finally, understanding eco-corona formation will be critical to unveil the complex NP interactions occurring in natural aquatic systems.