Prospective study on macroplastics and microplastics within dredging sediments

Plastic waste and their fragments (microplastics, <5 mm) are a global, persistent, and ubiquitous threat for ecosystems [1]. They are ingested by numerous species, which could cause harmful effects [2], [3]. Only few studies had investigated the presence of microplastics within terrestrial ecosystems [4]. However, soils/sediments may represent an important sink for microplastics [5], [6]. To fill this gap, four pits were dug within a dredging disposal area along the Aa River (France), and samples were taken at four depths with a metal trowel. Macroplastics and microplastics were extracted using sieves (5 and 10 mm) and a gravity separation method (NaI, 1.6 g mL-1), respectively. Plastics were observed under a dissecting stereo-microscope (6-50× magnifications), separated into 5 shape categories (fibers, fragments, micro-beads, films and foams) and analyzed to determine their plastic nature with a FTIR spectrometer. Observations suggest that these sediments are widely contaminated, with 1 to 77 macroplastics per kilogram and between 1 and 2822 microplastics per kilogram. No clear patterns were observed between sediment features and plastic concentrations. Films were the most abundant macroplastic shape, whereas microplastics were mainly fibers and fragments. FTIR results indicated that plastics were mainly made of polyethylene, polypropylene, polyvinyl chloride, polyamide and polyester.