A preliminary study of the interactions between microplastics and citrate-coated silver nanoparticles in aquatic environments

Microplastics and silver nanoparticles (AgNPs) are considered two emerging environmental contaminants that have adverse effects on aquatic environments. Knowledge on the interactions between AgNPs and microplastics may improve our understanding of these pollutants, posing to surrounding environments and public health. However, current knowledge regarding this issue is limited. Here, we investigate, for the first time, the interactions between AgNPs and the microplastics polyethylene (PE), polypropylene (PP), and polystyrene (PS) in aquatic environments. Results showed no significant interactions between AgNPs and PE or PP microplastics. However, AgNPs were efficiently removed by PS microplastics. These differences are mainly attributed to the presence of π-π interactions. Meanwhile, AgNPs aggregations were generated due to higher concentrations of leaching additives derived from PS microplastics. Interestingly, AgNPs are significantly captured on PS microplastic surfaces in the form of Ag0 rather than Ag+. The capture process is a monolayer adsorption and influenced greatly by the mass ratio of AgNPs and PS microplastics. These observations may provide a novel environmental fate of AgNPs, and indicate a new potential method for their removal to some degree. These findings demonstrate the complexities of AgNPs absorption onto microplastics and enhance present understanding of interactions between nanoparticles and microplastics in aquatic environments.