Nanoplastic transport in aqueous environments: The role of chemo-electric properties and hydrodynamic forces for nanoplastic-mineral interaction.

The fate and transport characteristics of nanoplastic (NP) through different environmental systems is largely governed by physio-chemical processes and their specific interaction with environmental constituents (i.e., minerals, dissolved species, suspended particles). A hydrodynamic component present in almost all terrestrial and marine aqueous environments impact the physio-chemical processes micron-scale is largely overlooked in NP transport studies. Therefore, we tested the interaction behavior of nanosized plastic polystyrene particles of various coatings in the presence of minerals abundant in the Earth crust within a hydrodynamic continuum representing flow rates from groundwater to surface water systems. Our batch experiments show that particle-mineral adsorption is largely driven by the magnitude of opposite charge configurations, which is either produced by mineral type or specific nanoplastic surface coating. Zetapotential serves as a good predictor of adsorption between uncoated and carboxyl-coated polystyrene with minerals. It fails, however, to predict adsorption behavior between NH2 coated polystyrene and apatite or feldspars, due to the more complex and varying compositions of these minerals. Incorporating the hydrodynamic force component into the particle- mineral interaction scheme reproduces those adsorption trends at slow flowrates of 1e-04 m/d. However, increasing flow rates by a factor of 100 modifies charge-driven adsorption between minerals and plastics. This study highlights the unabating importance of hydrodynamic conditions when predicting nanoplastic transport in different subsurface environments, and has implications for nanoplastic behavior in both terrestrial and marine aqueous environments.