Microplastic abundance in beach sediments of the Kiel Fjord

We assessed the abundance of microplastic (0.2 - 5 mm) in drift line sediments from three sites in Kiel Fjord, Western Baltic. The first site is intensively used by beach visitors, the second is in close proximity to a sewage plant and the third is polluted with large-sized plastic litter. Samples were split into three grain size classes (0.2 – 0.5, 0.5 – 1.0, 1.0 – 5.0 mm), washed with a calciumchloride solution and filtered at 0.2 mm. Filters were then visually inspected and a total of 180 fragments were classified as microplastic, of which 39 % were analysed using Raman spectroscopy. At the site with intense beach use as well as at the site that is close to a sewage plant 1.8 and 4.5 particles (fibers plus fragments) per kg of dry sediment were found, respectively, while particle abundances reached 30.2 per kg of dry sediment at the site with high litter loads. Our data suggest that intensity of human use and proximity to a sewage plant are not necessarily reliable predictors for high loads of microplastics in beach sediments, while the fragmentation of large plastic debris at site seems to be a relevant contamination source.