A novel, highly efficient method for the separation and quantification of plastic particles in sediments of aquatic environments

Although plastic debris is constantly accumulating in aquatic environments, the impact on aquatic ecosystems is not yet fully understood. A first important step to assess the consequences of plastic debris in aquatic ecosystems is the establishment of a reliable, verified, and standardized method to quantify the amount of plastic particles in the environment. We improved the density separation approach by the construction of the so called Munich Plastic Sediment Separator (MPSS). It enables a reliable separation of different ecologically relevant size classes of plastic particles from sediment samples. A ZnCl2-solution (1.6-1.7 kg/L) as separation fluid allows for an extraction of plastic particles ranging from large fragments to small microplastic particles (S-MPP, <1 mm). Subsequent identification and quantification of the particles with spatial resolution down to 1 μm can be performed using Raman microspectroscopy. Our study is the first providing validated recovery rates of 100% for large microplastic particles (L-MPP, 1-5 mm) and 95.5% for S-MPP. The recovery rate for S-MPP, using the MPSS, was significantly higher than the value obtained by application of classical density separation setup (39.8%). Moreover, our recovery rates were significantly higher than those based on froth flotation (55.0% for L-MPP) commonly used in recycling industries. Hence, our improved method can be used for a reliable and time-efficient separation, identification and quantification of plastic fragments down to S-MPP. This will help foster studies quantifying the increasing contamination of aquatic environments with microplastic particles, which is a crucial prerequisite for future risk assessment and management strategies.