Investigating microplastics and nanoplastics released from food bag ziplock using SEM and Raman imaging

Abstract Microplastic contamination is a concern in our daily lives, such as being released from self-sealing ziplock (sliderless zipper) plastic bags that are commonly used for food storage. That is because during the closure and opening process, due to friction and deformation, the male rim inserting into or separating from the female rim can release debris as micro- and nanoplastics (MNP). Herein, we initially observed the released debris using scanning electron microscopy (SEM). Subsequently, Raman imaging was employed to directly visualise the debris, either scratched on the rim surface or fallen down from the rim, from molecular spectrum perspective. Raman imaging analyses MNP from hundreds to thousands of spectra rather than from a single spectrum or peak, enhancing the signal-to-noise ratio statistically and providing morphological information for quantification. The confocal Raman-based mapping of MNP may be susceptible to be false images, which can be improved through terrain 3D mapping. Additionally, the weak signal of nanoplastics can be enhanced by reducing scanning pixel size and deconvoluting with surface-fitting algorithm. Consequently, we estimated that approximately 5(±3) MNP per millimetre along the ziplock length may be released during each closure/opening process. Given the use of these plastic bags for food storage, this level of contamination is concerning, warranting careful risk assessment alongside other potential MNP sources of plastic items used in our kitchens. Overall, Raman imaging can be effectively analyse MNP and more broadly nanomaterials, with help of algorithms and SEM.