Electrochemical properties of nanoplastics and their importance in transport through terrestrial groundwater ecosystems

, Müller Sascha, Balic-Zunic Tonci, Posth Nicole.

The subsurface is considered a key sink for plastic polymers in the environment. The presence of preferential flow paths, e.g. along cracks and fractures, but also the variety of geochemical and microbiological processes, however, challenge such a hypothesis. This is especially relevant for nanoplastic (NP) transport, as their physical entrapment (straining) may be less effective in subsurface pore space compared to larger microscale plastics. Accordingly, Nanoplastic particle transport is governed by the groundwater ecosystem chemistry that varies with the geological host material. A complex interplay between the NP particle with its surrounding host media (particle-particle, particle-solvent, particle-porous media) is largely driven by hydrogeochemical and microbiological conditions. Electrochemical properties of both the plastic particles and the host medium serve as crucial factors influencing nanoplastic transport behavior. We here use Zetapotential (ZP) to measure the electrochemical properties of nano-sized polystyrene particles in model groundwater systems under changing chemical conditions (pH, different ions, ion valency, ionic strength). Particular focus is on the influence of surface coatings (i.e.,COOH groups) as well as common minerals (i.e., Quarz, Feldspars) and sediment types of the subsurface (i.e., Quartenary sands, Miocene sands). A simple 1D- particle interaction model (DLVO-theory) is used to quantitatively derive potential interaction schemes between NP and subsurface media. Those information can guide us in further upscaling experiments from a 1D space to a 2D space (i.e. column experiments). Taking together, these efforts inform whether NP may be harbored or transported under a variety of subsurface conditions and trace the physical and biogeochemical mechanisms mediating this transport behavior.

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