Studies to evaluate methodologies used for determining heavy metal content in polyethylene terephthalate food packaging

Goodlaxson, Bradley
Major Professor
Keith Vorst
Committee Member
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Food Science and Human Nutrition

Increased consumer awareness of contamination in food-contact packaging has raised global concerns due to the potential of environmental contamination from packaging upon disposal after the service lifetime. Contamination in virgin and recycled polymers used for food-contact packaging has necessitated the development of analytical methods that identify and quantify heavy metals. Heavy metal contaminants in food-contact plastics have the potential to cause health issues if leaching were to occur. Sample preparation and analytical methods were evaluated to quantify heavy metal content in polyethylene terephthalate (PET). Since PET is one of the most widely used polymers for food-contact applications, accurate quantification of heavy metal content is essential to ensuring consumer safety. The two published acid digestion methods yielded incomplete sample digestion of PET, thus, additional methods were required for proper PET analysis. To circumvent this, modified microwave-assisted acid digestion methods were developed, which result in complete PET digestion and produce visually clear solutions. Analysis of the complete PET digests by inductively coupled plasma-optical emission spectrometry (ICP-OES) resulted in lead and antimony content values statistically higher than the two previously mentioned methods. To evaluate the ability of non-destructive methods to quantify heavy metal content in PET food packaging, X-ray fluorescence (XRF) was compared with ICP. Traditional analytical methods such as ICP are time-consuming and expensive processes. Moreover, testing if XRF technology can provide a means for monitoring heavy metal content in thin plastics would greatly reduce the frequency of sample testing by traditional methodology. Results from this analysis suggests that it is possible to evaluate thin plastic samples by developing a statistical model that estimates ICP data from XRF outputs. This research shows that XRF technologies can be applied to online systems for real-time monitoring of heavy metal contamination in food packaging plastics. The results of these studies indicate that while food-packaging plastics should be regarded as safe, previously published research has underestimated the 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.