Abundance, distribution, and composition of microplastics in the filter media of nine aged stormwater bioretention systems

• Published in: Chemosphere (Oxford) Vol. 320; p. 138103
• Main Authors: Lange, Katharina, Furén, Robert, Österlund, Helene, Winston, Ryan, Tirpak, R. Andrew, Nordqvist, Kerstin, Smith, Joseph, Dorsey, Jay, Viklander, Maria, Blecken, Godecke-Tobias
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.04.2023
• Subjects: Biofilter; Centre - Centre for Stormwater Management (DRIZZLE); Centrumbildning - Centrum för dagvattenhantering (DRIZZLE); LID; Microplastics; Plastic pollution; Plastics; Rain; Rain garden; Soil media; Urban runoff; Urban Water Engineering; VA-teknik; Soil media; Biofilter; LID; Urban runoff; Rain garden; Plastic pollution
• ISSN: 0045-6535; 1879-1298; 1879-1298
• DOI: 10.1016/j.chemosphere.2023.138103

Bioretention systems are designed for quality treatment of stormwater. Particulate contaminants are commonly treated efficiently and accumulate mainly in the surface layer of the bioretention filter material. However, concerns exist that microplastic particles may not show equal accumulation behavior as other sediment particles. So far only two field and two laboratory studies are available on the fate of microplastics in few relatively newly built bioretention systems. Therefore, this study investigated the abundance and distribution of microplastics in nine 7–12 years old stormwater bioretention systems. It was found that microplastics generally accumulate on the surface of bioretention systems. Microplastic median particle concentrations decreased significantly from the surface layer (0–5 cm) of the filter material to the 10–15 cm depth layer from 448 to 136 particles/100 g, respectively. The distance to the inlet did not significantly affect the surface accumulation of microplastic particles, suggesting modest spatial variability in microplastics accumulation in older bioretention systems. Further, this study investigated the polymer composition in bioretention systems. It was shown that PP, EVA, PS and EPDM rubber are the most abundant polymer types in bioretention systems. Also, it was found that large percentages of microplastic particles are black particles (median percentage of black particles: 39%) which were found in 28 of the 33 investigated samples. This underlines the importance of including black particles in microplastic studies on stormwater, which has been overlooked in most previous studies. [Display omitted] •Occurrence and accumulation of microplastics in aged bioretention systems.•Determination of polymer types including black particles.•Microplastics are accumulated mainly in the filter media top layer.•Highest microplastic concentrations in the forebays.•Up to 59% of the microplastics in the filter media are black particles.