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

Density separation can isolate microplastics from environmental samples containing sediment. Typically, a solution added to sediment causes microplastics with lower densities to float. The solution of choice can influence the recovery of different particles since denser solutions can separate a greater range of microplastics. The equipment and procedural complexity further influence density separation protocols and microplastic recoveries. Zinc chloride (ZnCl₂) is frequently used to isolate high-density polymers from environmental samples yet is rarely validated with simple, well-described protocols. A simple overflow method using ZnCl₂ to isolate microplastics from sediment samples is described following a 3-step process: (1. Separation) ZnCl₂ (1.7 g cm⁻³) solution is added to a sediment sample, agitated then settled; (2. Overflows) buoyant particles at the surface of the solution are overflowed twice; (3. Filtration) the overflowed solution is filtered. In a validation experiment with polyamide, rubber, polyvinyl chloride and polyethylene terephthalate/polyester, the mean recovery using this overflow method was 96 % ± 0.6 (standard error). This overflow density separation method proposes an accessible and reliable protocol to extract medium and high-density microplastics.