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Gradient columns to measure the density of microplastics.
Jessica L Stead1, Luan de Souza Leite2, Tom Bond1
1School of Sustainability, Civil and Environmental Engineering, University of Surrey, Guildford GU2 7XH, UK.
The Science of the Total Environment
|September 11, 2024
Summary
Density gradient columns accurately measured environmental microplastic density. Most plastics, primarily polyethylene, showed wide density variations, often linked to manufacturing additives rather than environmental factors.
Area of Science:
- Environmental Science
- Materials Science
- Analytical Chemistry
Background:
- Density gradient columns are a standard industrial technique for plastic density measurement.
- Application of density gradient columns to environmental plastic debris remains limited.
- Accurate density data is crucial for understanding microplastic behavior and fate.
Purpose of the Study:
- To assess the applicability and effectiveness of density gradient columns for environmental microplastics.
- To generate an extensive dataset on the density of microplastics from an urban beach.
- To investigate factors influencing microplastic density, including polymer type, additives, and environmental processing.
Main Methods:
- Utilized 14 density gradient columns to measure the density of 150 environmental plastic particles and 100 known microplastics.
- Established a density range of 800-1418 kg·m⁻³ for the columns.
- Calculated error margins for individual particles (≤0.27 kg·m⁻³) and polymer types (≤±1.78 kg·m⁻³ for 75% of polymers).
Main Results:
- Successfully measured the density of 92% of investigated environmental plastic particles.
- Polyethylene pellets exhibited a broader density range (823.47–1143.47 kg·m⁻³) than previously reported.
- Colored microplastics frequently showed altered densities, suggesting manufacturing additives/impurities are key factors, not environmental weathering or biofilm.
Conclusions:
- Density gradient columns offer a promising, accurate, and high-throughput method for analyzing microplastic density.
- This technique can significantly enhance understanding of microplastic characteristics and distribution.
- Manufacturing processes, specifically additives and impurities, play a more significant role in microplastic density variation than environmental degradation.
