Migration characteristics of microplastics based on source-sink investigation in a typical urban wetland

Although urban wetlands are key transition sub-ecosystems connecting urban microplastic pollution sources to freshwater environments, few studies have reported microplastic migration characteristics in urban wetlands. Recent studies have only focused on the occurrence of microplastics in wetlands. Thus, this study investigated the occurrence of microplastics in sources and sinks (surface water, sediment, effluent, and agricultural waste) and analyzed the migration characteristics of microplastics in a typical urban wetland, namely the Huixian Wetland, Guilin. The abundance of microplastics was in the ranges of 16.5–89.0 items/L, 16.8 × 103–52.8 × 103 items/kg, and 172.0–605.0 items/L in the surface water, sediment, and effluent, respectively. Most of the microplastic settlement at 1–2 km downstream of the source of pollution in this wetland presented with a total decrease of 53.7–61.4% for microplastics in the surface water, whereas microplastics of smaller sizes (100–500 µm) were retained more in surface water than the smallest (50–100 µm) and large (500–5000 µm) microplastics. Clustering analysis and principal component analysis showed that effluent was the major source of microplastics in the urban section of this wetland, and agricultural wastes also played a role in the suburbs. This first quantification of small-sized (50–500 µm) microplastic removal throughout an urban wetland provides key reference information for controlling the environmental risk of microplastics in aquatic environments.