Silver Migrates to Solid Foods and Abiotic Surfaces from Model Plastic Packaging Containing Silver Nanoparticles

Plastic food packaging containing silver nanoparticles (AgNPs) has received a lot of attention due to the antimicrobial properties of AgNPs, but these materials are not yet authorized for use in the United States. An important area of uncertainty is whether AgNPs can migrate to solid foods during prolonged direct contact. We manufactured laboratory-scale model food packages with AgNPs and low-density polyethylene (LDPE) and assessed the migration of Ag to four model foods under simulated long-term storage: cheese slices, wheat flour, spinach leaves, and ground rice. Ag migration was observed for all food types, regardless of the test conditions, with the amount of migration being dependent on both food particle size, food-polymer contact efficiency, and whether the Ag-contaminated food was washed prior to analysis. To explore migration mechanisms, we used laser-ablation ICP-MS and laser-scanning confocal microscopy to show that two types of model NPs (AgNPs and luminescent QDs) readily transfer out of polymers during long-term contact with abiotic surfaces, and transferred NPs were restricted largely to the surface of the material in contact with the NP-containing polymers. These experiments, as well as the migration experiments with foods, demonstrated that a liquid medium is not required to facilitate Ag migration out of AgNP-containing food contact polymers and that migrated Ag is likely located at the surface of contacted foods.