Interactions of nanoscale plastics with natural organic matter and silica surfaces using a quartz crystal microbalance.

Interactions of nanoscale plastics with natural organic matter (NOM) and silica surfaces were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Polyethylene and polystyrene are the most used plastic polymers and most likely to accumulate in the environment, and thus their nano-scale interactions were investigated in this study. Deposition and release of polyethylene and polystyrene nanoscale plastics were investigated on silica and NOM-coated surfaces in the presence of different salt types (NaCl, CaCl, MgCl) and ionic strengths (IS). Polyethylene nanoscale plastics showed negligible deposition on silica surface, while significant deposition of polystyrene nanoscale plastics was observed on silica surface. However, both polyethylene and polystyrene nanoscale plastics showed significant deposition on NOM-coated surfaces, with polystyrene showing higher deposition. Increased IS resulted in greater deposition of both polyethylene and polystyrene nanoscale plastics on NOM-coated surfaces due to the functional groups, following DLVO theory. Deposited polyethylene nanoscale plastics on NOM-coated surfaces can be remobilized whereas deposition of polystyrene nanoscale plastics was irreversible on both silica and NOM-coated surfaces. Overall, higher deposition of nanoscale plastics on NOM-coated surfaces indicates that fate and mobility of nanoscale plastics in the environment will be significantly governed by their interactions with NOM.