Flexible Wall Permeameters for Research on Microplastic Transport in Soil: Validity, Advantages, and Constraints

Yifei Gao ¹, Surya Sujathan ¹, Elizabeth A Carter ²

⁰School of Civil Engineering, The University of Sydney, Darlington, New South Wales 2008, Australia.

Environmental Science & Technology +

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July 8, 2025

View abstract on PubMed

Summary

Flexible wall permeameters (FWPs) show promise for studying microplastic (MP) transport in soils, offering better control than rigid columns. FWPs are effective for MP transport of ≤1 μm particles, especially when filter papers are avoided.

Area Of Science

Environmental Science
Soil Science
Environmental Engineering

Background

Microplastics (MPs) are pervasive soil contaminants.
Rigid wall columns have limitations in studying MP transport, particularly in low-permeability soils.
Flexible wall permeameters (FWPs) offer superior control over boundary conditions and leakage, presenting an underexplored alternative for MP transport studies.

Purpose Of The Study

To evaluate the suitability of FWPs for microplastic transport research.
To assess potential artificial retention of MPs by FWPs and its impact on experimental validity.
To provide guidance for effective FWP utilization in soil MP transport studies.

Main Methods

Mass-balance experiments were conducted using FWPs under varying conditions.
Parameters tested included FWP components, pressure gradients, ionic strengths, and MP characteristics (size, concentration).
MP flow-through experiments were performed on sandy and bentonite clay soil samples.

Main Results

Baseline MP mass recoveries exceeded 80%, decreasing for larger MPs (>5 μm) and high ionic strengths.
MP agglomeration and filter paper retention were identified as primary causes of mass loss.
FWPs demonstrated effectiveness for MP transport studies of particles ≤1 μm at ionic strengths <0.03 M, with optimal recovery when filter papers were omitted.
FWPs were confirmed as suitable soil columns for MP transport in sandy and clay soils.

Conclusions

Flexible wall permeameters are a viable tool for microplastic transport research in soils.
Careful consideration of MP size, ionic strength, and filter paper use is crucial for accurate results.
FWPs provide a controlled environment for studying microplastic fate and transport in various soil types.

Keywords:

flexible wall permeameter mass recovery microplastic retention spectrophotometry transport