Detection of Small Microplastics in Milk Powder by Raman Spectroscopy and Environmental Scanning Electron Microscopy: Analytical Challenges and Metrological Perspectives

Microplastic (MP) pollution represents an emerging threat to terrestrial and aquatic ecosystems. These contaminants can easily enter the food chain, raising concerns about their potential impact on human health, the environment, and food safety [1]. Determination of MPs in complex samples has long be challenged by a lack of method harmonization and quality assurance tools such as certified reference materials for MP analysis, hindering data comparability and traceability. The smaller the microplastic particles are, the more challenging it is to isolate and identify them from complex matrices, without compromising their integrity. Another critical aspect is the cross-contamination which can negatively affect analytical performance and reliability. This study focuses on the development of a multi-technique analytical workflow based on μRaman spectroscopy and Environmental Scanning Electron Microscopy [2] for the detection, identification, and quantification of small-sized MPs (SMPs) (10-100 µm) in infant formula powdered milk. . Both primary and secondary particles of polystyrene (PS), polyethylene terephthalate (PET) were considered as representative test materials. In particular, PET reference materials were provided by BAM within the PlasticTrace European project. Cleanroom best practices were implemented developing a multi-step cleaning procedure to minimize cross-contamination. After filtration on silicon filters (5 µm), Raman parameters were fine-tuned to prevent laser-induced degradation. ParticleFinder™ and IDFinder™ software enabled automated particle counting and polymer identification. Matrix removal was achieved through a combined enzymatic digestion and alkaline treatment [3], preserving SMPs integrity. Spiking experiments in milk powder showed excellent recovery rates (85-120%) for all polymers investigated. Further activities will involve the determination of reporting limits based on blank values (ISO/NP 16094-2), analysis of real samples and participation in inter-laboratory testing schemes. [1] M.A. Mir, M.A.A. Khan, B.K. Banik, S.M. Hasnain, L. Alzayer, K. Andrews, S.I. Abba, Emerg. Contam. 11 (2025) 100477 [2] M. Mattarozzi, F. Bianchi, M. Maffini, F. Vescovi, D. Catellani, M. Suman, M. Careri, Talanta 196 (2019) 429-435 [3] P.A. Da Costa Filho, D. Andrey, B. Eriksen, R.P. Peixoto, B.M. Carreres, M.E. Ambühl, J.B. Descarrega, S. Dubascoux, P. Zbinden, A. Panchaud, E. Poitevin, Sci. Rep. 11 (2021) 24046