Cryogrinding and sieving techniques as challenges towards producing controlled size range microplastics for relevant...

Area of Science:

• Environmental science
• Ecotoxicology
• Materials science

Background:

• Microplastic (MP) pollution impacts aquatic organisms, necessitating realistic laboratory assessments.
• Pearl oysters (Pinctada margaritifera) in French Polynesian lagoons encounter MPs from degraded farming equipment.
• Accurate characterization of MP size is crucial for understanding their ecological effects.

Purpose of the Study:

• To produce microplastics (MP) within a specific size range (20-60 μm) for Pinctada margaritifera ingestion studies.
• To evaluate an established method for generating MPs from environmental plastic waste.
• To accurately characterize the size distribution of generated MPs, including smaller microplastics and nanoplastics (MNP).

Main Methods:

• Mechanical cryogenic grinding and liquid sieving were used to process plastic pearl farming equipment.
• Coulter counter analysis (2 μm cut-off) and laser diffraction analysis (0.4 μm cut-off) were employed for particle size distribution.
• Scanning electron microscopy was used for microstructure characterization and to investigate particle self-assembly.

Main Results:

• The protocol generated MPs in the target 20-60 μm range but also produced a significant excess of smaller particles (<3 μm).
• Laser diffraction revealed that 80-90% of particles were <1 μm, indicating a substantial nanoplastic fraction.
• Scanning electron microscopy suggested spontaneous particle self-assembly into superstructures, explaining the discrepancy between expected and observed size distributions.

Conclusions:

• The applied method for MP production requires refinement due to the overproduction of small particles and nanoplastics.
• Particle self-assembly is a significant technical challenge that can lead to underestimation of micro- and nanoplastics (MNP).
• Precise characterization of MNP size distribution is essential for reliable ecotoxicological assessments and avoiding overestimation of effects.