Evaluation of methods for determining heavy metal content in polyethylene terephthalate food packaging

Increased consumer awareness of heavy metal content in virgin and post-consumer recycled polymers for direct food-contact packaging has necessitated developing analytical methods that identify and quantify heavy metals. Two common acid digestion methods incompletely digest polyethylene terephthalate samples and, thus, additional methods are required to properly analyze polyethylene terephthalate. This study developed two modified microwave-assisted acid digestion methods resulting in complete polyethylene terephthalate digestion, which subsequently produced visually clear solutions. Inductively coupled plasma-optical emission spectrometry analysis of the completely digested polyethylene terephthalate resulted in heavy metal concentrations statistically higher for lead and antimony than for the methods that did not completely digest the polyethylene terephthalate polymer. This study indicates that previously published research results might have unintentionally created bias toward lower heavy metal contamination in polymers used for food packaging. This is of concern when considering end-of-life disposal for food packaging with regulatory threshold levels for specific and total heavy metal content.