Homogeneity of Sand-Sized Microplastics Concentration and Polymer Assemblage in Beach and Coastal Dune Sediments

Microplastics impact marine and terrestrial environments as vectors of chemical pollution, stunting the growth of dune plants and posing a threat to coastal ecosystems. Because they are more easily transported by wind from the beach environment into the coastal dunes than mineral sand grains, dune sediment ought to be relatively enriched in microplastics. To test this hypothesis, the concentrations and polymer assemblage of sand-sized (0.1-1 mm) microplastics (MPs) in surface sediment were compared between intertidal beach (marine) and coastal dune (aeolian) samples at two different UK coasts (mid-Wales adjacent to the Irish Sea and southeast England adjacent to the English Channel) using FT-IR microscopy. Results show no differences in polymer composition, diversity, or abundance between beach and dune sediments. Average concentrations reached hundreds of MPs/kg, and their composition was dominated by rayon and polyester fibers. The lack of expected microplastics enrichment of the coastal dunes by preferential aeolian transport from the adjacent beach is attributed to the severe supply limitation of these particles at the sediment surface interface compared with the transport-limited movement of wind-blown mineral sand. Our findings suggest that mitigation of microplastics contamination may focus on the beach environment, as its condition is mirrored in the dune sediment.