Label-free detection and characterization of secondary microplastics from tea bags

Microplastics impose a major threat to the environment and biota. Reported release of secondary microplastics from tea bags while brewing tea results in their direct ingestion into the human body. The results reported here indicate the presence of variety of plastic materials and point to further need for investigations on the presence of micro- and nanoplastics from plastic packaging materials. In this work, the presence of microplastics from tea bags diffused into boiled water is explored using a multimodal approach comprising of digital holographic microscopy (DHM) and micro-Raman spectroscopy. The leachates derived from the tea bag into water while brewing was analyzed using DHM and micro-Raman spectroscopy, which helped in the detection, characterization, and identification of the detected microplastics. A systematic analysis of 11 teabag samples indicates the presence of plastic materials such as polyethylene, polyvinyl chloride, nylon, etc. in a variety of shapes within micrometer sizes. The morphology, size, concentration, and chemical structure of the microparticles are characterized using nondestructive techniques with minimum sample preparation. The imaging results are complemented and validated using scanning electron microscopy. DHM and micro-Raman spectroscopy are sufficient for the detection and identification of secondary microplastics demanding only a very small volume of samples.