Abundances of large microplastics (L-MP, 500-5000 µm) in surface waters of the Weser estuary and the German North Sea (April 2018)

In order to assess pollution with large microplastics (L-MP, 500-5000 µm) in the Lower Weser and transition to the German North Sea, surface water samples were collected with the RV Otzum (ICBM, Institute for Chemistry and Biology of the Marine Environment), as well as with the RV Uthörn (AWI, Alfred-Wegener-Institute) in April 2018. Sampling was performed using a microplastic net (mesh size: 300 µm), followed by filtration in the laboratory over a 500 µm stainless steel sieve. Putative MP items in the size range 500-5000 µm were analysed by means of Attenuated Total Reflection - FTIR in order to determine the underlying synthetic polymer. Dominant polymer type in the L-MP sample fraction was polyethylene. Concentrations ranged between 1 × 10⁻² m⁻³ and 9.8 × 10⁻¹ m⁻³. The highest MP concentration was measured upstream the Weser Weir.