Effect of storage time on release of microplastics (MPs) from different milk packaging

The growing detection of microplastics (MPs) in the human body has raised concerns about the potential entrance of MPs into the food chain and subsequently into humans. Due to wide consumption of milk by different age groups, investigating the MPs release into milk during storage time from different commercial milk packaging materials is crucial. MPs release in three common packaging types of ESL milk (bottles and packets) and sterilized milk (multi-layer carton) during storage periods (expiration date) was studied. The milk samples were digested with KOH, passed through a vacuum filter, and the filter paper was examined under a microscope to investigate the characteristics (size, color, and shape) of the MPs. The MPs were transferred to copper adhesive glue by sterile insulin needle, and the polymer type and surface morphology of the particles (elemental composition) were determined by confocal Raman spectroscopy and SEM-EDX, respectively. The MPs release increased with storage time in all packaging types. The detection of no MPs in Raw milk confirmed the contamination from processing and packaging. Raman spectroscopy identified polyethylene, polypropylene, and polycarbonate as the dominant polymers, originating from packaging materials, caps, and processing equipment. Also, high-fat sterilized milk released significantly more MPs than low-fat milk, suggesting that milk fat enhances polymer degradation. The estimated daily intake ranged from 0.090–0.934 (adults) to 0.253–2.616 (children) MPs particles/day/kg BW, indicating higher intake in children. The findings indicate the need for improved packaging quality, shorter recommended storage periods, and regulatory standards for MPs in dairy products.