Comparing Methods for Optimising Microplastic Extraction in Sediment Through Density Separation

Abstract

Oceans constitute a sink of microplastics, mostly accumulating in sediment. Microplastic extraction in sediment is challenging leading to diverse methodologies. However, a standardised methodology that facilitates comparison among studies is needed. We compared the efficiency of commonly used solutions for density separation and two transferring methods for microplastic recovery. A CaCl2-saturated solution with the spill method was the most efficient, recovering 90 ± 1% of microplastics regardless of the polymer, size and shape; being safer, cheaper, and faster than the second-best alternative, ZnCl2 with the spill method. Recovery of high-density polymers was challenging, especially for low-density solutions (e.g. NaCl) or the overflow method. Although size ranges did not influence microplastic recovery for CaCl2 with the spill method, overall, larger microplastics had better extractions. Shape influenced PET fibres recovery, being especially low for NaCl and to some extent for ZnCl2 and CaCl2. Adding H2O2 or NaCl + H2O2 enhanced fibre extraction. We propose employing CaCl2 and the spill method as a standard protocol to maximise MP extraction from sediment and comparability among studies. If H2O2 has been used as a pretreatment could be used in an initial extraction run. This methodology could be used in similar matrices, such as soil.

Keywords: Hydrogen peroxide, Spill method, Overflow method, Extraction method comparison, Bio-based microplasticss