Analytical protocol assessment for microplastic and microfiber isolation in milk: a preliminary study of contamination in raw milk samples

Microplastics (MPs) and microfibers (MFs) are emerging contaminants in food, with milk representing a critical concern due to its importance in human nutrition, particularly for vulnerable populations. This study aimed to optimize an analytical protocol for isolating MPs and MFs in milk samples and to assess contamination levels in raw milk collected at farms. The digestion method employed hydrogen peroxide (30% v/v) at optimized temperatures (40°C for commercial milk and 50°C for raw milk), followed by vacuum filtration. Method accuracy was evaluated through recovery experiments using spiked reference materials, and then the extraction protocol was applied to raw milk samples from mechanical milking. Results revealed average concentrations ranging from 1.3±0.5 to 5.5±5.0 MPs and synthetic MFs per 100 mL, with natural MFs accounting for 47% of total particles detected. Chemical characterization through Fourier transform infrared spectroscopy identified polypropylene (41%), polyester (6%), and polyvinyl chloride (6%) as the predominant polymer types, suggesting contamination from milking equipment and textile materials. No significant differences in contamination levels were observed across sampling days or among individual cows, indicating systematic contamination along the production chain. This study provides a validated analytical approach for monitoring MP contamination in milk and establishes baseline data for raw milk contamination at farm level, supporting the development of mitigation strategies along the dairy supply chain.