Nanoplastic in Aqueous Environments: The Role of Chemo-Electric Properties for Nanoplastic-Mineral Interaction

Abstract

The ever-increasing plastic production and its continuous release of primary and secondary nanoplastic particles (NP) (particles <1000µm) to the environment is an emerging contaminant for terrestrial environmental systems. Its fate and transport characteristics in the subsurface are still not fully understood, as those environments are highly complex with high mineral, chemical, biological and morphological heterogeneity. Our study focuses on the interaction between major abundant minerals occurring in the subsurface and NP under simplified water chemical conditions (1mM KCl, pH 5.5). Therefore, potential chemical effects from ions in solution can be excluded, and only the effect of mineral complexity can be assessed. Various surface-modified polystyrene nanoparticles serve as proxies for degradation (-COOH) or protein associations (-NH2) occurring in plastics in environmental settings. Here, we also compare our experimental results to DLVO double-layer force estimates. All minerals studied maintained negative charges across pH changes. Therefore, we hypothesize that adsorption behaviour is mainly “surface charge” driven (Zeta potential). Furthermore, we discuss other mechanisms, such as specific ion-binding interactions occurring in the presence of metal ions, bridging mechanisms and hydrogen bonding. Our study indicates that biogeochemical and mineralogical composition is a controlling factor in NP attachment and release processes in subsurface environments and, thus, crucial for transport in aquifers.

Keywords: nanoplastic, mineral, nanoplastic- mineral interaction, groundwater, adsorption