Evaluating the retention of airborne microplastics on plant leaf: Influence of leaf morphology

Airborne microplastics (AMPs) have been identified in both indoor and outdoor environments and account for a large portion of an individual's daily exposure to microplastics. Thus, it is crucial to find effective methods to capture and control the levels of AMPs and ultimately reduce human exposure. While terrestrial plants have been recognized for their effectiveness in capturing airborne particles, little is known about their ability to capture AMPs. This study investigated the ability of 8 natural plant species and 2 artificial plants to capture AMPs, as well as the influence of leaf morphology on this retention. Plant leaves were exposed to AMPs for two weeks, and deposited MPs were characterized using a Micro-Fourier Transform Infrared spectrometer (μ-FTIR). Selected cleaned leaves were further digested, and the presence of subsurface MPs was confirmed using μ-Raman. Results revealed that AMPs were retained on the leaves of all selected plant species at concentrations ranging from 0.02 to 0.87 n/cm2. The highest average concentration was observed on an artificial plant with fenestrated leaves, followed by natural plant species with trichomes and leaflets. The lowest concentration was observed on a natural plant with smooth leaves. The majority (90%) of retained AMPs were fibres, and the remaining were fragments. PET was the prominent polymer type. Additionally, MP fragments were observed in the leaf subsurface in one selected species, likely retained within the leaf cuticles. The results suggest that plant leaves can indiscriminately retain AMPs on their surfaces and act as temporary sinks for AMPs. Additionally, indoor plants may provide a useful functional role in reducing indoor AMP concentrations, although longer-term studies are needed to ascertain their retention capacity more accurately over time and to evaluate the capability of indoor plants to act as a suitable, cost-effective candidate for reducing AMPs.