Microplastic contamination in commercial milk: Quantification and polymer identification using SEM-EDS and...

Microplastic (MP) contamination in food products has raised global public health concerns, yet standardized methodologies for dairy matrices remain lacking. This study investigated the presence, abundance, polymer composition, and size distribution of microplastics in 30 commercially available milk samples from Tehran, Iran, and evaluated the association between packaging type and contamination levels. MPs were isolated through chemical digestion (30% hydrogen peroxide, 60°C, 24 h) and vacuum filtration (1.2 μm glass fiber filters). Quality assurance included polymer-specific recovery tests (82-96% for five polymer types), procedural blanks (1.2 ± 0.8 particles per filter), and airborne contamination monitoring. Suspected MPs were detected in all samples, with concentrations ranging from 5 to 36 particles per liter (mean: 18.4 ± 8.7 particles per liter). Among the particles subjected to Micro-Raman analysis, polyethylene (32%), polypropylene (24%), polyethylene terephthalate (15%), polyamide (12%), and polyethersulfone (9%) were identified. Packaging type was significantly associated with MP abundance (p < 0.001), with plastic bottles (24.6 ± 7.1 particles per liter) showing higher contamination than Tetra Pak cartons (12.2 ± 5.9 particles per liter). Particle size distribution showed that 72% of particles were <100 μm, with a mean diameter of 68.4 ± 42.7 μm. These findings indicate that commercial milk may represent a potential dietary exposure pathway for microplastics. The observed association between packaging type and MP abundance suggests a possible contribution of packaging-related factors, although the specific sources of the detected particles cannot be established from the present observational design. Further studies using targeted source-tracking approaches and standardized analytical methods are warranted.