Leaf morphology affects microplastic entrapment efficiency in freshwater macrophytes

Context In contrast to marine environments, microplastic pollution in freshwater systems is understudied. Previous research suggests that freshwater macrophytes function as microplastic sinks, which, because they are at the base of food webs, has implications for higher trophic levels. Aim This study compares the ability of freshwater plants with different leaf morphologies to trap downwelling microplastics. Method Microplastics (800–1000 µm polyamide grains) were deposited onto three macrophyte species, namely, Cabomba caroliniana, Egeria densa, and Hygrophila polysperma. Microplastic mass retained was calculated as the percentage of microplastic mass captured by the plant and standardised microplastic retention was calculated as the absolute microplastic mass retained (g) divided by plant dry mass (g). Results The amount of trapped microplastics differed significantly among species, with the highest amount trapped by C. caroliniana (39.3%; 7.91 g g-1), followed by E. densa (28.8%; 5.30 g g-1) and H. polysperma (17.6%; 4.47 g g-1). Conclusion Significant differences in microplastic retention among species may be attributed to variation in leaf morphology. Implications These findings have potential applications in bioremediation and biomonitoring, where freshwater macrophytes could help with the tracking and mitigation of microplastics in the environment.