Determining Changes in Permeability Caused by the Retention and Transport of Microplastics in Saturated Sand Columns

Microplastics (MPs), synthetic polymers less than 5 mm in size, are an environmental pollutant of emerging concern. MPs are formed, in part, by fragmentation of plastics released to the environment into smaller pieces. MPs have been detected in ocean, soil, freshwater, drinking water and groundwater. Limited laboratory and field experiments demonstrate that MPs are retained and transported in porous media of a groundwater aquifer. However, a research gap exists regarding the effects that MPs retention and transport have on aquifer physical properties, specifically permeability. The goal of this research is to determine whether the retention and transport of polyethylene (PE) MPs alter the permeability of saturated silica sand by conducting a series of controlled, constant head column experiments . We hypothesize that PE MPs retained in the sand column after the transport will decrease the permeability. Permeability changes are measured by considering the influence of MPs concentration , solution fluid, flow rate and ionic strength. Cylindrical columns are filled with 0.7-0.8 mm coarse silica sand and saturated prior to each MPs transport experiment. A MP solution with a pre-determined concentration of PE microspheres are added into the column using a peristaltic pump. Outflow samples are collected, samples are prepared with vacuum filtration, and final PE concentrations are counted using a reflected light microscope. Changes in permeability are measured by constant-head tests using a Trautwein M100000 Standard Panel permeameter, which will hold a constant hydraulic gradient across the column. T he results of this novel research will increase our understanding of how and under which conditions aquifer properties change during the MPs retention and transport. MPs that enter an aquifer may alter the porous media permeability, thereby decreasing groundwater flow and damaging aquifer viability. This could cause a permanent reduction in the availability of freshwater for human use and consumption, considering that groundwater systems constitute a huge source of drinking water. Thus, this research represents valuable knowledge to determine the transport, fate, and remediation alternatives of MPs in groundwater.