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Microplastics Journey in Wetland Ecosystems: From Air to Microlayer, to Subsurface Water and Sediment
Summary
Scientists studying an Iranian wetland found that tiny plastic particles (microplastics) build up heavily at the water's surface, like a thin plastic "skin", and settle into sediment, with most of it blowing in from road dust rather than washing in from rain. The wetland took in far more plastic than it released, meaning these ecosystems act like sponges that trap and store microplastics for months at a time instead of flushing them away. Since wetlands often connect to drinking water sources and food chains, this buildup matters, it suggests the plastics we breathe in from road dust don't just disappear, they can accumulate in the environments we and
This study provides a short-term, dry-weather multi-compartment assessment of microplastic (MP) contamination in the Choghakhor Wetland, a vital freshwater ecosystem in western Iran. We quantified MPs in air, subsurface water, the surface water microlayer (SML), and sediments and developed a first-order mass-balance framework to clarify transport and fate. The SML showed much higher MP concentrations than the subsurface water when converted to volumetric units, while method-specific SML estimates varied among approaches (4.4–13.8 MP m⁻² using a glass tube; 196–982 MP m⁻² using a sieve; and 130–1754 MP m⁻² using filter paper). Subsurface water contained 0.083–1.5 MP L⁻¹, and the two sediment samples contained 60–400 MP kg⁻¹. Atmospheric deposition during the monitored intervals reached 2363 MP m⁻² h⁻¹. Flux analysis indicated that dry-weather influx exceeded observed outflux by more than three orders of magnitude. Using the conservative combined-outlet scenario, the wetland residence time was at least 168 days, whereas a water-only outlet scenario yielded ∼344 days. FLEXPART suggested that road dust dominated modeled source contributions, with smaller agricultural and soil-related contributions, although site-specific attribution remains model-based. These findings identify wetlands as important sinks and reservoirs of MPs, while emphasizing that the present results represent a dry-weather baseline rather than seasonal or annual conditions.