Microplastics in urban and highway stormwater retention ponds

Urban and highway stormwater runoff seems an obvious pathway for conveying microplastics from land-based sources to the aquatic environment. The significance of this pathway is however largely unknown. This study presents first results on microplastics in urban and highway stormwaters by analysing microplastics (10-2000 mu m) in the water phase of stormwater treatment ponds in the North of Jutland, Denmark. The stormwater of seven ponds treating runoff drained from different landscapes were studied. Ponds serving highway and residential areas had the lowest microplastic concentration, while ponds serving areas with industry and commerce had the highest. The stormwater of the ponds contained 490-22,894 items m(-3), corresponding to an estimated 85-1143 mu g m(-3). The dominating polymers were polypropylene, polyvinylchloride, polyester, polyethylene and polystyrene. There was a tendency towards polyvinylchloride particles being the largest in size, while a mixed group of less common polymers were the smallest. Residential ponds generally held the largest microplastic particles and were in many aspects quite comparable to one another, in terms of concentrations, sizes, and polymer composition. This study shows that land-based sources are significant contributors to MP in the environment. It demonstrates that the stormwater retention ponds act not only as pollution hotspots, but also play a role in the transport of MP from land to the aquatic environment. (C) 2019 The Authors. Published by Elsevier B.V.