Identification and quantification of common microplastics in table salts by a multi-technique-based analytical method

Microplastics (MPs) are considered as contaminants of emerging concern to the environment and our food chains in recent years. In this study, we presented a multi-technique-based analytical method for detection of MPs through a combination of microscope-FTIR (μ-FTIR) with pyrolysis-GC/MS (Py-GC/MS) to achieve 3-dimensional (3D) information for the identification of polymer type, characterization of particle size and morphology, and quantification of MPs based on both particle number and mass of plastics. Plastics that are commonly used and disposed of, including polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), poly vinyl chloride (PVC), polyamide (PA), and poly(methyl methacrylate) (PMMA), were covered in this study. Sample extraction and separation procedures were optimized for these microplastics in table salts where good recoveries (> 75%) were achieved. To further enhance the detection sensitivity in simultaneous quantification of multiple polymers in a sample, a serial dissolution approach with different solvents was developed for the detection of all 7 types of plastics. The established sample preparation process and multi-technique-based analytical method were validated with polymer standards in table salts, resulting in satisfactory qualification and quantification for all samples tested. A retail survey of MPs in table salts was conducted with the developed analytical method, revealing that MPs were present in all commercially available table salts. The total number of MP particles varied from 20 to 125 particles/kg and the total mass contents of seven types of plastics ranged from 30 to 530 µg/kg in table salts.