Collaborative Research: Surface Properties and Transport of Micro- and Nanoplastics in Unsaturated Soil

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Plastic pollution of terrestrial ecosystems is an emerging threat to soil health. While there is much known about plastics pollution in marine ecosystems, little is known about fate and transport of micro- and nanoplastics in terrestrial systems. Micro- and nanoplastics may be held up in soil, thereby negatively impacting soil organisms, or they may move through soil, potentially contaminating groundwater and drinking water resources. This project aims to characterize the fate of micro- and nanoplastics in terrestrial systems, so that the environmental hazards posed by micro- and nanoplastics can be assessed. Plastic particles in soil will be tracked over time to determine whether their chemical properties change and how they move.Four commonly used plastics will be used: polyethylene, polypropylene, polystyrene, and a typical biodegradable plastic. The plastics will be subjected to environmental weathering by exposing them to UV and rainfall. Micro- and nanoplastics will then be thoroughly characterized for size, shape, and surface and colloidal properties. It is expected that the weathered micro- and nanoscale plastics particles form an "eco-corona", i.e., a covering with extracellular substances, soil organic matter, and clay minerals, which makes the particles more hydrophilic and mobile in soils. Surface and colloidal properties of the plastics will be characterized. Further, transport of the plastics in soils and groundwater will be quantified to determine whether micro- and nanoplastics are held up in soils or aquifers. The specific objectives of this project are to (1) understand the creation of secondary micro- and nanoplastics during weathering, (2) determine the role of weathering on the surface and colloidal properties of micro- and nanoplastics, and (3) identify the fundamental mechanisms involved in transport of micro- and nanoplastics in unsaturated porous media and soils. The project will provide mechanistic information on mobility of micro- and nanoplastics under saturated and unsaturated flow conditions. The project will also provide valuable information for policy makers on the degradation of biodegradable plastics in terrestrial environments. Biodegradable plastics are a promising alternative to conventional plastics, particularly for single-use applications. The results will help inform legislation on the use of biodegradable plastics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.