Invisible plastic release from overlooked usage practices in microwaved food packaging.

Plastic food packaging is an overlooked source of invisible contamination during microwaving. In this study, polyethylene (PE) residues released from microwaveable food packaging, including onigiri wrappers, porridge cartons, and milk cartons, were investigated under microwave conditions representative of routine consumer use. PE release increased markedly with heating duration. Nile Red fluorescence staining showed that microplastic size decreased from 3.88 ± 0.28 μm to 3.18 ± 0.23 μm during prolonged heating. Dynamic light scattering analysis revealed nanoplastic particles within 1-3 min of microwave heating, with sizes ranging from 40 to 240 nm. Surface-enhanced Raman spectroscopy showed that polyethylene residues released from onigiri wrappers reached 1443.78 ± 5.28 μg/mL after 5 min of microwave exposure. Exposure to these residues decreased the viability of Clone 9 normal rat liver cells and increased oxidative stress. These findings suggest that neglected usage patterns may contribute to invisible plastic contamination, raising concerns about food safety.