A Simple Method for Quantifying and Characterizing Microplastics at Ultra-Low Concentrations

Introduction: Microplastics (MPs) can be defined as synthetic polymer particles ranging in size from 0.1 to 5,000 µm [1]. Currently, a knowledge gap exists in MPs research regarding validation through recovery tests at very low contamination levels (e.g., 0-10 particles) [2–4]. The aim of this study was to develop a simple method for spiking samples with as few as a single particle, while enabling accurate characterization of their size, shape, and morphology.

Methods: Polyethylene MPs (fragments, approximately 30-150 µm in size) were transferred onto filters using an optical microscope and metal tweezers. Particles were then added or removed until the desired number was reached. Counted and photographed MPs were transferred by rinsing the filters with 100 mL of pre-filtered ultrapure water into a separate container. Three particle levels (1, 5, and 10 particles) were prepared in triplicate. Recovery was assessed by filtering the samples and recounting MPs. Characterization was conducted using optical microscopy and scanning electron microscopy.

Results: The recovery testing method was successfully developed, and characterization of MPs was performed. Particle recoveries of 100.00% ± 0.00%, 80.00% ± 20.41%, and 93.33% ± 28.12% were achieved for 1, 5, and 10 particles respectively.

Conclusions: Our method enables sample spiking and full characterization of MPs based on their size, shape, and number, including at the single-particle level. It addresses the current knowledge gap in precise MPs recovery assessment at low contamination levels (e.g., 0-10 particles).

This research was funded by the National Science Center, Poland, OPUS 25 Grant number NR2023/49/B/N29/0061.

Literature:

[1] EFSA CONTAM Panel. EFSA Journal, 2016, 14, 6, e04501

[2] Badzoka et al., 2025. Microplast. Nanoplast., 5, 2

[3] Weis et al., 2021. Appl. Sci., 11, 8529

[4] Sarlin et al., 2024. Discov. Environ., 2, 102