Understanding microplastic retention in surface flow constructed wetlands: The impact of aquatic macrophytes

Microplastics are increasingly entering both natural and constructed wetlands, but their distribution, retention, and interactions with aquatic macrophytes remain poorly understood. This study investigated the fate and retention of three common types of microplastics — polyethylene microbeads, tire wear particles, and polyacrylonitrile fibers — each introduced at a concentration of 547 particles/L into a laboratory surface flow constructed wetland. The experimental setup included unvegetated and vegetated experiments with four submerged macrophytes of different leaf morphology and a floating macrophyte to evaluate the role of vegetation in microplastic retention and their impact on plant health over 12 days. The results showed that the majority of microplastics are associated with the air-water or sediment-water interfaces after entering the wetland. Fibers and tire wear particles were mainly found in the sediment, regardless of the presence of vegetation. Of the microbeads, 25 % settled in the unvegetated wetland, while 56 % were found in the sediment of the vegetated constructed wetland, suggesting that vegetation promotes the settling of buoyant microplastics. Overall, the constructed wetland exhibited high retention efficiency for all microplastic types, with over 99.9 %, regardless of the vegetation present. Microplastics were observed to attach to macrophytes, and plant morphology was a key factor influencing retention. No significant effects on the electron transport system and only minor, non-particle-specific effects on chlorophyll a content were observed. These results highlighted the effectiveness of constructed wetlands in retaining microplastics and the need for further research on the interactions between plants and microplastics to optimize wetland design for microplastics management. • Surface flow constructed wetlands retained over 99.9 % of microplastics. • Vegetation increased retention of buoyant polyethylene microbeads. • Fibers and tire wear particles predominantly settled in the sediment across all setups. • Leaf morphology influenced retention efficiency of plants. • Presence of microplastics had minor negative effects on plants.