New Perspective on the Mobilization of Microplastics through Capillary Fringe Fluctuation in a Tidal Aquifer Environment

Abstract

The presence of plastic fragments in the environment is a growing global concern. In this study, we explored the effects of dynamic fluctuations of capillary fringe on the transport of microplastics (MPs) in the substrate combining various environmental and MP properties. Both experimental and Hydrus-2D modeling results confirmed that increasing cycles of water table fluctuation led to the rise of capillary fringe. An increase in the cycles of water table fluctuations did not significantly change the overall MP retention percentages in 0.5 mm substrate but altered the MP distribution along the column. In 1 and 2 mm substrate, the increase in cycle numbers enhanced the MP transport from substrate to the water below. In terms of the size of the MPs, more 20−25 μm polyethylene (PE2) were retained in the substrate compared to 4−6 μm polyethylene (PE1) under the same number of fluctuation cycles. High-density polytetrafluoroethylene (PTFE, 5−6 μm) exhibited higher retention percentages compared to PE1 particles. Ultraviolet aging for 60 days enhanced PE1 transport along the column, while 60 days of seawater aging did not affect PE1 transport greatly. For PTFE, ultraviolet and seawater aging enhanced its retention in the substrate. The retention percentages of both PE1 and PTFE in the column increased with the elevated ionic strength and the decrease of fluctuation velocity. This work highlights that capillary fringe fluctuation can serve as a pathway to relocate MPs to the tidal aquifer.

The Urgent Need to Investigate Microplastic Contamination in Groundwater: Soil and Groundwater Interactions as Key Drivers

“…25 Groundwater flow characteristic is one of the dominant factors that controls the migration and distribution of MPs, especially the sudden change in flow rate. A high water velocity facilitates the longer 25 In addition, the biodegradation and biochemical breakdown of MPs can lead to their fragmentation into smaller particles or nanoplastics. 27 On the contrary, the extent to which changes in groundwater biochemistry resulting from hydrodynamic and hydrochemical variations affect the transformation of MPs remains unclear.…”

“…Specifically, stagnant zones, air–water and water–solid interfaces, have been recognized as effective locations for the retention of MPs within the aquifer . MPs can easily percolate through porous media if the porosity of the matrix is significantly larger than that of the particles, or particles form clogging layers to restrict further movement . Groundwater flow characteristic is one of the dominant factors that controls the migration and distribution of MPs, especially the sudden change in flow rate.…”

“…23 MPs can easily percolate through porous media if the porosity of the matrix is significantly larger than that of the particles, or particles form clogging layers to restrict further movement. 25 Groundwater flow characteristic is one of the dominant factors that controls the migration and distribution of MPs, especially the sudden change in flow rate. A high water velocity facilitates the longer 25 In addition, the biodegradation and biochemical breakdown of MPs can lead to their fragmentation into smaller particles or nanoplastics.…”

Overlooked Role of Bulk Nanobubbles in the Alteration and Motion of Microplastics in the Ocean Environment

“…28,29 The vertical distribution of MPs is also influenced by the tides. 30,31 There have been many studies examining the influence of polymer characteristics and traditional environmental parameters on the behavior of MPs in shoreline environments. 32 However, there are a number of substances present in the ocean that have yet to be investigated, and as such the impact of these substances on the marine environment and the fate and transport of pollutants is not yet well understood.…”

“…Another important factor is the condition of currents and waves. Strong currents can transport MPs over long distances, carrying them from one part of the shoreline to another or out to sea. , The vertical distribution of MPs is also influenced by the tides. , …”