A comparison of microscopic and spectroscopic identification methods for microplastic analysis

Abstract

The analysis of microplastics in various environmental samples requires the identification of microplastics from natural materials. The identification technique lacks a standardized protocol. Herein, stereomicroscope and Fourier transform infrared spectroscope (FT-IR) identification methods for microplastics (< 1 mm) were compared using the same samples from the sea surface microlayer (SML) and beach sediment. Fragmented microplastics were significantly (p < 0.05) underestimated and fiber was significantly overestimated using the stereomicroscope both in the SML and beach samples. In the fragment, many transparent or white fragments were identified as synthetic polymers, such as polyethylene (PE) and polypropylene (PP) by FT-IR, but were not counted as microplastics using the microscope. And less than 1 mm sized fragment had a limitation of identification by microscope. In the fiber, plastic-like fibers such as sea grass and cotton were apparently miscounted as microplastics. The total abundance by FT-IR was higher than by microscope both in the SML and beach samples, but they were not significantly different because of the offset of the fragments and fiber in abundance. Depending on the number of samples and the microplastic size range of interest, the appropriate identification method should be determined selecting a suitable identification method for microplastics is crucial for evaluating microplastic pollution.nfrared spectroscope (FT-IR) identification methods for microplastics (< 1 mm) were compared using the same samples from the sea surface microlayer (SML) and beach sediment. Fragmented microplastics were significantly (p < 0.05) underestimated and fiber was significantly overestimated using the stereomicroscope both in the SML and beach samples. In the fragment, many transparent or white fragments were identified as synthetic polymers, such as polyethylene (PE) and polypropylene (PP) by FT-IR, but were not counted as microplastics using the microscope. And less than 1 mm sized fragment had a limitation of identification by microscope. In the fiber, plastic-like fibers such as sea grass and cotton were apparently miscounted as microplastics. The total abundance by FT-IR was higher than by microscope both in the SML and beach samples, but they were not significantly different because of the offset of the fragments and fiber in abundance. Depending on the number of samples and the microplastic size range of interest, the appropriate identification method should be determined selecting a suitable identification method for microplastics is crucial for evaluating microplastic pollution.