Shapes of Hyperspectral Imaged Microplastics

Area of Science:

• Environmental Science
• Analytical Chemistry
• Materials Science

Background:

• Microplastic shape is critical for understanding their environmental fate and impact.
• Current shape definitions for hyperspectral imaging are ambiguous, hindering data comparability.
• A standardized classification system is needed for microplastic research.

Purpose of the Study:

• To propose and validate a clear, concise set of microplastic shape categories for hyperspectral imaging.
• To assess the distinguishability and representativeness of these categories across diverse environmental matrices.
• To promote harmonization and reproducibility in microplastic research.

Main Methods:

• An expert-based survey was conducted to define microplastic shapes.
• Five experts validated proposed categories (fiber, rod, ellipse, oval, sphere, quadrilateral, triangle, free-form, unidentifiable) on 11,042 microplastic images.
• Images were sourced from indoor air, wastewater, marine water, and stormwater samples.

Main Results:

• Proposed shapes were found to be well-defined, representative, and visually distinguishable, particularly fiber and sphere.
• Ellipse, oval, and rod shapes were less distinguishable but prevalent in water and solid matrices.
• Smaller microplastics (<30 μm) in indoor air frequently appeared as unidentifiable shapes.

Conclusions:

• The proposed shape categories enhance the clarity and consistency of microplastic analysis.
• Assessing category recognizability is vital before data reporting to ensure comparability.
• Standardized shape definitions are essential for advancing microplastic research and policy.