Fluxes, residence times, and the budget of microplastics in the Curonian Lagoon

This study examines the distribution and abundance of microplastics (MPs) in the Europe's largest coastal lagoon, Curonian Lagoon, and adjacent Baltic Sea, focusing on water, surface sediment, and atmospheric deposition. Fibrous MPs, predominantly 1000-5000 μm in size, were the most prevalent across all environments. White/transparent MPs dominated sediment and atmospheric deposition, while blue/green MPs were most abundant in water. Low-density polymers accounted for 70 % of MPs in water, whereas high-density polymers were dominant in sediment (62 %), with equal proportions found in atmospheric deposition. The average MP concentration was higher in the lagoon (1.7 ± 1.2 MP L^-1) compared to the Baltic Sea (1.3 ± 0.4 MP L^-1), with an estimated 66.7 × 10⁹ MP year^-1 Flowing from the lagoon into the sea. Atmospheric deposition introduced a substantial MP influx, estimated at 27.8 × 10¹² MP year^-1, exceeding the river influx of 20.7 × 10⁹ MP year^-1. MP deposition was higher in terrestrial environments (72.5 MP m^-2 day^-1) than in aquatic environments (60.4 MP m^-2 day^-1 in the sea and 48.3 MP m^-2 day^-1 in the lagoon). The estimated MP budget in lagoon water was 10.8 × 10⁹ MP particles, with a residence time of approximately 27 days. MP concentrations in surface sediment (405.7 ± 192.9 MP kg^-1) indicate long-term accumulation, suggesting substantial MP deposition in lagoon sediments. Atmospheric transport modeling (FLEXPART) identified Europe, Russia, and oceanic sources as key contributors, alongside local inputs from agriculture, sea spray, and road dust. Understanding MP dynamics in coastal ecosystems is urgent to inform mitigation strategies, regulatory policies, and risk assessments, particularly given the long-term accumulation in sediments and potential for ecological harm.