A simple overflow density separation method that recovers >95% of dense microplastics from sediment

Area of Science:

• Environmental Science
• Analytical Chemistry
• Materials Science

Background:

• Microplastic contamination is a significant environmental concern, necessitating effective isolation techniques from complex matrices like sediment.
• Density separation is a common method, but the choice of solution and protocol complexity impact microplastic recovery rates.
• Zinc chloride (ZnCl2) is used for high-density polymer separation but lacks standardized, simple protocols.

Purpose of the Study:

• To describe and validate a simple, accessible overflow density separation method using zinc chloride for microplastic extraction.
• To evaluate the efficiency and reliability of the proposed method for recovering medium and high-density microplastics from sediment.

Main Methods:

• A three-step overflow method using a 1.7 g cm-3 zinc chloride solution was developed.
• Steps included: agitation and settling of sediment in ZnCl2, overflowing buoyant particles twice, and filtering the overflow.
• Validation involved testing recovery rates with known microplastics: polyamide, rubber, polyvinyl chloride, and polyethylene terephthalate/polyester.

Main Results:

• The developed overflow density separation method demonstrated a high mean recovery rate of 96% ± 0.6% (standard error).
• The protocol proved effective for isolating a range of medium and high-density microplastics, including polyamide, rubber, PVC, and PET/polyester.

Conclusions:

• The described zinc chloride overflow method offers an accessible, reliable, and efficient protocol for microplastic separation from sediment samples.
• This method addresses the need for validated, simple procedures in microplastic analysis, improving consistency and accuracy in environmental monitoring.