Aggregation of original and UV-aged polypropylene microplastics under the intervention of glomalin-related soil protein

Glomalin-related soil protein (GRSP) plays vital role in the soil aggregate development, and its interaction with microplastics may affect the migration behavior of plastic particles in the environment. However, the binding of GRSP with the microplastics and the physicochemical characteristics of their composite remain poorly understood. Here, the binding behavior and potential mechanism of GRSP with micron-grade original polypropylene (OPP) and aged polypropylene (APP) were investigated using morphological characterization and microscopic analysis techniques. The aggregation of microplastics occurred with the addition of GRSP, and the aggregation of APP particles was more evident owing to the 24.5 % higher adsorption capacity of APP than that of OPP. The adsorption of GRSP on microplastics led to fluorescence quenching, indicating that the interaction between GRSP and microplastics resulted in the transformation of the molecular structure of GRSP. Calculations of binding sites and constants suggested that microplastics and GRSP exhibited strong binding affinities and that aged microplastics were more likely to bind with GRSP. These binding sites involve the carboxylic acid and alcohol hydroxyl groups of the polysaccharide components of GRSP. Furthermore, aged microplastics reacted with GRSP through the newly formed C-O/C O bonds and enhanced hydrogen bonding interactions, increasing the ability of the microplastics to interact with GRSP. These findings revealed the interaction characteristics and mechanisms between GRSP and microplastics at the macro and molecular scale, providing new insights into the environmental behaviors of microplastics and soil remediation strategies related to GRSP regulation. • GRSP mitigates the migration risks of microplastics by promoting their aggregation. • Aging of microplastics enhances GRSP adsorption by providing more binding sites. • Microplastics cause GRSP molecular transformation and fluorescence quenching. • C-O/C O and hydrogen bonding play vital role in the GRSP binding to microplastics.