Ethanol, not Water, Should Be Used as the Dispersant When Measuring Microplastic Particle Size Distribution by Laser Diffraction

Zheng Fang*, Brett Sallach, Mark Edward Hodson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Size distribution is a crucial characteristic of microplastics (MPs). A typical method for measuring this property is wet laser diffraction. However, when measuring size distributions of MPs, despite it being a poor dispersant for many MPs, water is commonly selected, potentially limiting the reliability of reported measurements. To evaluate dispersant suitability, different aqueous concentrations of ethanol (0, 10, 20, 30, 40, 50, 75, 100 wt%) and aqueous solutions of 0.001 wt% Triton X-100 and a mixture comprising 10 wt% sodium pyrophosphate and 10 wt% methanol were used as dispersants in a laser granulometer (Mastersizer 2000) to determine particle size distributions (PSDs) of granular polyethene MP35, MP125 and MP500 particles (nominally described as < 35, < 125 and, < 500 μm in size). The reliability of the reported PSDs depended on the dispersant used and size of primary MPs. With increasing ethanol concentrations, PSD curves of MP35 particles shifted from multi-modal to mono-modal distributions. The measured size distribution reduced from 1588.7 - 4.5 μm in water to 39.9 - 0.1 μm in 100 wt% ethanol. Generally, as ethanol concentration increased uncertainty associated with the PSD parameters decreased. Although Triton X-100 and the mixed solution also showed better dispersion than water, their measured sizes and COV (%) were notably larger than those for 100 wt% ethanol. Similar trends were observed for larger-sized MP125 and MP500 particles, but differences in PSD curves, PSD parameters, and COV (%) among dispersants were less pronounced. In all dispersants, the volume weighted mean diameters (VWMD) in 100 wt% ethanol (MP35: 14.1 μm, MP125: 102.5 μm, MP500: 300.0 μm) were smallest and close to microscopy results (MP35: 14.6 μm, MP125: 109.0 μm, MP500: 310.6 μm). Therefore, for accurate determinations of the PSDs of MP by wet laser diffraction, ethanol rather than water should be used.
Original languageEnglish
Article number166129
JournalScience of the Total Environment
Early online date11 Aug 2023
Publication statusPublished - 1 Dec 2023

Bibliographical note

© 2023 The Authors


  • MPs
  • Aggregation
  • Floating
  • Laser granulometer
  • PSD
  • Polyethylene

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