Insights into the interaction of microplastic with silver nanoparticles in natural surface water

The combined pollution induced by microplastics (MPs) and other pollutants, such as nanomaterials, has received increasing attention. The interaction between MPs and silver nanoparticles (AgNPs) may affect both their behaviors in natural environments, however, knowledge on these effects remains limited. In this study, AgNPs and three common MPs, polypropylene (PP), polyethylene (PE), and polystyrene (PS), were co-exposed to natural freshwater and brackish water to investigate the interaction between MPs and AgNPs in natural surface water. The results showed that the environmental behaviour of AgNPs in natural freshwater and brackish water is first of all affected by water chemistry and only in second instance affected by MPs. In natural freshwater, AgNPs remained stable largely dominated by dissolved organic matter (DOM), parts of which were subsequently captured by three MPs in the form of single particles without significant difference. In contrast, both ionic strength and DOM contributed to the aggregation of AgNPs in natural brackish water. PE and PP captured a small amount of AgNPs in the form of aggregates in natural brackish water, while the majority of AgNP aggregates were trapped by PS in natural brackish water. Therefore, both water chemistry and MPs types were found to play crucial roles in the interaction between MPs and AgNPs. These observations also revealed that MPs could serve as carriers for AgNP transport and advance the current understanding of combined pollution between MPs and engineered nanomaterials in natural aquatic environments.