Visual and spectral identification of microplastic particles from soil matrices: a comparison between Stereomicroscope, FTIR and LDIR methods

The research on microplastic pollution is escalating due to greater awareness and concern about this environmental contaminant. Many methods exist to detect microplastics from different matrices, such as soil or water. However, uncertainties remain on how accurate and efficient the detection and identification of the number and types of microplastic polymers are. Specifically for the soil matrices, microplastic identification is challenging due to the frequent high levels of organic matter content. This study aims to compare and highlight the advantages and disadvantages of the following identification methods: stereo-microscope, μFTIR (4x and 15x magnification) and LDIR. These were tested after the extraction of microplastics from soil matrices. Various types of samples were used per method: 16 environmental from agriculture fields; 8 blank chemicals; 12 virgin microplastic polymers including PE, PLA, PVC and PBAT-PLA blend. Half of the environmental and blank samples were spiked with the same virgin microplastic polymers to test the microplastic limit of detection for each method. Data is still under analysis. Preliminary results suggested that the efficiency of each method depends on different factors such as the type of soil, tested microplastic polymers, and specific information on the number, size or type of microplastic polymer. Hitherto, we conclude that there is no single method capable of identifying a wide variety of microplastics to a high degree of efficiency. A combination of different methods would provide more accurate results than a single method of detection for microplastics.