Development and validation of analytical methods to detect small microplastics (10 -100 µm) in infant formula milk powder

It has been proven that microplastics (MPs), plastic particles less than 5 mm (ISO GUIDE 35:2017(E)), can be found in various food items (e.g., milk, drinking water) demonstrating the potential risk of human exposure via the food chain. Among these products, milk, being a staple in many diets, has garnered attention due to its widespread consumption and nutritional significance. The sources of MPs contamination in milk are multifaceted: environmental pollution, agricultural practices and processing methods (e.g., plastic packaging and equipment used during milking). However, the potential health implications of MPs ingestion through milk consumption remain a subject of ongoing research. Various analytical techniques have been employed to detect and quantify MPs in milk. Neverthless, metrologically validated analytical methods for MPs detection, identification and quantification in complex food matrices are still lacking. In this work, in the framework of 21GRD07PlasticTrace project, a new methodology was developed to accurately determine and characterize MPs in infant formula milk powder using vibrational spectroscopy techniques, micro-Raman and micro-FTIR. Before the analysis, both enzymatic and chemical (alkaline conditions) digestion, and a final filtration step through a silicon filter (pore size 5 mm) were conducted to remove the organic matter of the milk matrix. This methodology was developed and validated for different polymers using both commercially available reference materials with defined sizes and morphologies (polyethylene, polystyrene) and a more representative polydisperse reference material obtained by milling procedures (polyethylene terephthalate). These reference materials were used to spike the milk matrix to optimize the different sample pre-treatment steps, and to demonstrate their negligible effect on the characteristics and polymer compositions of the MPs. This methodology will be further applied in commercial infant formula sourced from supermarket shelves to evaluate the MPs contamination of real samples. Also see: https://micro2024.sciencesconf.org/558867/document