Microplastics in Dutch marine sediments

To gain an indication on the amount of plastic in Dutch marine sediments, for this research project 4 marine sediment locations monitored by Rijkswaterstaat (Vlissingen, Noordwijk2, Kornwerderzand and Bocht van Watum) were chosen. At each location 3 samples were taken. In total 24 samples were analysed. These samples were analysed for the presence of microplastics in the size ranges of 100-300 ?m, 300-1000 and 1000-5000 ?m (according to OSPAR technical specifications). The plastics that were identified were polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), polyurethane (PU), polyvinylchloride (PVC), and polyester. In all 24 samples microplastics were found. For the size fraction from 100-300 ?m the particle numbers stretched over the various locations from 479±386 p/kg dry weight (d.w.) to 13931±4872 p/kg d.w. Various types of plastic (PE, PS, PP, PU, PA, PVC and polyester) were found during this study. However, PU was only found at one location and polyester at two out of eight. All other polymers were found at every location. By far the largest particle number was found for PE followed by PP. The lowest particle numbers were found for PU and PET. In the size fraction from 300-1000 the particle numbers are lower compared to the more tiny size fraction and vary between 134±190 and 619±316 p/kg d.w. In this size fraction no polyester was detected and PU was merely found at one location. Also in this larger fraction PE is the most abundant plastic followed by PP. There were no particles found larger than 1000 ?m in any of the locations. The smallest particle number over the whole range from 100-5000 ?m is 882±732 and largest number is 13931±4872 p/kg d.w. It can been seen that the particle number drops with the particle size mounting. On average, in all size fractions the most abundant polymer with regard to particle number is PE (75%) followed by PP (19%). The other polymers have a mean abundance between nearly 0 and 4%. When the mean particle number of all samples (5558 p/kg d.w.) is translated into mass of plastic per kg, a mean total polymer mass of about 4.5 mg/kg d.w. is found in these samples. The amount of plastic ranges from 0.04 to 22 mg/kg d.w.