Transport of micron-sized polyethylene particles in confined aquifer: Effects of size, aging, and confining pressure

Contamination of groundwater by microplastics (MPs) is increasingly reported and attracts a growing attention due to their potential risks. To understand how MPs migrate into groundwater, many previous works have investigated their transport using man-made microspheres of few microns or smaller as models. However, MPs observed in the environment are more diverse in size, shape, and type, which may have different migration behaviors. In this work, the transports of irregularly shaped polyethylene (PE) particles in the sand packed column were studied. Small MPs (22-37 μm) generally have high mobility than large MPs (44-74 μm) but can also be affected by aging. Aging decreased the hydrophobicity of the MPs and increased their surface negative charge, which can facilitate the transport of MPs. However, the physical barrier of space in the porous media might have a greater influence on their transport. The retention of the MPs was enhanced with the increase of pressure due to compression that decreased pore size. Results from this study showed that MPs of environmental features can also be transported in the groundwater but the processes could be governed by different factors, such as physical interception and steric hindrance.