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Six polymers (polypropylene, polyethylene, polystyrene, polyvinyl chloride, polyethylene terephthalate and polyamide) were prepared containing additives chosen to be representative of those typically used in plastic materials and articles intended for contact with food. Test plastics containing the selected additives at concentrations typically used in the manufacture of food contact plastics were moulded into sheets. Control plastics were also prepared in which no additives were incorporated.
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A database of ingredients and similes was prepared and a literature search was carried out to establish any actual or likely reactions of the ingredients and their similes, alone or in combination, under the conditions used to manufacture the test plastics. From this literature search a theoretical list of possible impurities/degradation/reaction products was prepared for each of the plastic/additive combinations.
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A suite of analytical methods focussing on the analysis of substances with molecular weights below 1,000 Dalton, in view of toxicological significance, were applied to the plastics themselves and to extracts of the materials with and without the additives. Analytical methodology used included thermodesorption gas chromatography-mass spectrometry (GC-MS) to detect very volatile substances, GC-MS and GCxGC-time of flight (TOF)-MS to detect semi-volatile substances and liquid chromatography (LC)-TOF-MS and LC-Fourier transform (FT)-MS to detect non-volatile substances. By comparing the chromatograms obtained for the analysis of the plastic and additive samples with those obtained from the analysis of the plastics only, any additional substances present were identified. The additives used in the manufacture of the test plastics were analysed in the same way such that any impurities present in the starting materials were detected. Internal standards were added to the plastics prior to extraction and the concentrations of any NIAS detected were estimated based on their relative responses. All six plastics were also analysed by nuclear magnetic resonance spectroscopy.
Food packaging materials made of plastics may contain substances that are not used intentionally and do not appear in lists of permitted ingredients. These substances may be present as impurities in the starting materials used to make the plastic or as reaction or decomposition products formed during polymerisation to make the plastic or during thermal processing of the plastic to make the packaging. These substances are commonly referred to as NIAS (non-intentionally added substances). The compliance of food contact plastics with existing legislation should take into account both (a) known ingredients and (b) their impurities, reaction products and breakdown products. To date most studies have concentrated on the former and have largely neglected the latter.
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The main aim of this project was to identify and catalogue the NIAS derived from starting substances used to make six major food contact polymers. As there are hundreds of combinations of plastic formulations and manufacturing conditions then the project was carried out to take the lead in the analytical chemistry aspects of risk assessment of reaction products and breakdown products of some of the most commonly used food contact materials. In this way it has provided information about the principles, practicalities and likely outcome of the assessment of this class of substances.
<p>Find more about this project and other FSA food safety-related projects at the <a href="http://www.food.gov.uk/science/research/" target="_blank">Food Standards Agency Research webpage</a>.