Migration of heavy metals from recycled polyethylene terephthalate during storage and microwave heating

Agencies such as the Environmental Protection Agency and Agency for Toxic Substances and Disease Registry are pushing for increased use of recycled polyethylene terephthalate. Packaging materials made from recycled polyethylene terephthalate are used for direct food contact in recycled rigid containers and films. Most recycled polyethylene terephthalate packaging materials contain heavy metal catalysts, the most common being antimony. The recycling process has the potential to increase degradation products, chemical additives and polymerization side-products. Recent studies using inductively coupled plasma-atomic emission spectrometry confirmed the presence of cadmium, chromium, lead, nickel and antimony in food packaging. These heavy metals have the potential to migrate onto and into food products, and limited governmental regulation of these contaminants in recycled polyethylene terephthalate packaging materials increases public health risks. In this study, 22 samples of known heavy metal content were tested for heavy metal migration of lead, cadmium, chromium, nickel and antimony into a 5% aqueous citric acid solution or deionized water. Samples were exposed for 5 min to microwaves from a 1700 W microwave oven set to 70% power, or were stored at 7.2 or 22.2℃ for 1, 7 or 14 days before testing. The samples were analyzed for heavy metal content per ASTM E1613-04, the standard test method for the determination of lead by inductively coupled plasma-atomic emission spectrometry. Neither the storage nor the microwave treatments had a significant effect on heavy metal migration, while exposure to 5% aqueous citric acid resulted in a higher rate of heavy metal leaching from the recycled polyethylene terephthalate compared to samples exposed to deionized water. A very low percentage of the samples tested had heavy metals migrate above detectable levels indicating that most recycled polyethylene terephthalate packaging materials are relatively safe for direct food contact.