Contribution of the root system of Cyperus papyrus and Pontederia sagittata to microplastic removal in floating treatment Wetlands in two urban ponds

Microplastic pollution represents a global challenge that threatens ecosystems and human health. Because of this, there has been an increased interest in evaluating the use of phytotechnologies as a natural alternative for the removal of microplastics in water bodies. This study assessed the microplastic removal by Floating Treatment Wetlands (FTWs) consisting of linear arrays planted with Cyperus papyrus and Pontederia sagittata, installed in two urban ponds (“Pond 1” and “Pond 4”) located in the center of the city of Xalapa, Veracruz, Mexico. The results indicated that the two linear arrays of FTWs in Pond 1 (FTW1 and FTW2) efficiently removed microplastics in water column and sediments, with total removal rates of 82.4% and 81.1% respectively, despite having a high initial microplastic concentration. On the other hand, the effectiveness of the two FTWs in Pond 4 was mainly attributed to the first line of plants (FTW3), where the highest removal rates were observed, showing 61.6% in water column and 72.6% in sediments. However, the total removal of the two lines was 64.6% in water and 48.8% in sediments. C. papyrus and P. sagittata plants strongly retained microplastics in their roots, with concentrations of 16.4 and 11.9 mg/g respectively for FTW1 and FTW2 in Pond 1, and 2.1 and 6 mg/g for FTW3 and FTW 4 in Pond 4. These results suggest that the main removal microplastic mechanism was root retention, which facilitates microplastic removal from the aquatic environment by periodical root harvesting. Therefore, the crucial role of roots in the stabilization and reduction of these pollutants is highlighted. This study represents the first report in Mexico on the efficiency of FTWs in removing microplastics in urban water bodies.