Comparison and uncertainty evaluation of two centrifugal separators for microplastic sampling

Area of Science:

• Environmental Science
• Analytical Chemistry
• Oceanography

Background:

• Filtration-based microplastic sampling faces challenges balancing high throughput with size discrimination.
• Small microplastics (<100 µm) are often underrepresented in sampling studies.
• Accurate quantification of microplastics is crucial for understanding environmental impact.

Purpose of the Study:

• To introduce and evaluate two novel centrifugal separators (hydrocyclone and continuous flow centrifuge) for efficient microplastic sampling.
• To assess the retention efficiency of these separators for particulate plastics in estuarine waters.
• To conduct the first expanded uncertainty calculation in microplastic research using established metrology guidelines.

Main Methods:

• Development and optimization of hydrocyclone and continuous flow centrifuge methods for microplastic separation.
• Application of optimized methods in an extensive sampling study of estuarine waters.
• Identification and quantification of microplastic polymer types and size distributions.
• Bottom-up uncertainty evaluation based on the "Guide to the expression of Uncertainty in Measurement" (JCGM 100:2008).

Main Results:

• Microplastic concentrations in estuarine waters ranged from 193 to 2072 particles/m³.
• Dominant polymer types identified include polypropylene, acrylates, polyvinyl chloride, and polyethylene.
• Over 95% of sampled microplastic particles were smaller than 100 µm.
• Relative expanded uncertainty varied significantly (24% to >200%), highlighting the importance of uncertainty assessment.

Conclusions:

• Centrifugal separators offer an efficient alternative to filtration for sampling small microplastics.
• Significant uncertainty in microplastic measurements necessitates critical reevaluation of existing literature data.
• Standardized uncertainty evaluation is essential for reliable microplastic research and policy-making.