Novel Single-Particle Analytical Technique for Inhalable Airborne Microplastic Particles by the Combined Use of Fluorescence Microscopy, Raman Microspectrometry, and SEM/EDX.

Abstract

This study presents a novel and efficient method for analyzing inhalable airborne microplastics (AMPs) in ambient PM10 aerosols. Although many studies have been conducted on MPs in a variety of environments, the physicochemical characteristics of AMPs of inhalable size (<10 μm) in ambient PM10 are poorly understood because of the lack of suitable analytical methods. The method employed in this study combines fluorescence microscopy, Raman microspectrometry (RMS), and scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDX) for an efficient and reliable investigation of inhalable AMPs, which constitute a small portion of ambient PM10 aerosol particles. Fluorescence microscopy and staining are used to select particles with high MP potential from ambient urban PM10 aerosols. The combination of RMS and SEM/EDX then allows for a detailed characterization of these particles on a single-particle basis. The results of the study show that ∼0.008% of the particles collected using a PM10 sampler had high MP potential, corresponding to ∼800 particles/m3. Among the stained particles of <10 μm, 27% were determined to be plastic, while the remaining 73% were found to be from tire/road wear. The number of inhalable AMPs was estimated to be 192 (±127) particles/m3. This study provides an important insight into the characteristics of inhalable AMPs in ambient PM10 aerosols that are particularly critical in respect of human health and climate change. The authors highlight that the use of a single fluorescence staining method can overestimate the number of inhalable AMPs in ambient air by including tire/road wear particles. To the best of their knowledge, this is the first study to demonstrate the morphological and spectroscopic characteristics of the same individual inhalable AMPs.