A03054: An investigation into the reaction and breakdown products from starting substances used to produce food contact plastics

Study Duration: September 2005 to August 2007

Contractor: Central Science Laboratory (Lead Contractor) TNO Nutrition and Food Research (Additional Scientific Contact)

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.

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.

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.

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.

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.

Many peaks were detected in the chromatograms of the test plastics that were not in the control samples. Some could be attributed to the additives themselves, others were present as impurities in the additive starting substances and several were predicted reaction/breakdown products that would previously have been reported as unknowns. However, for some plastics there remained a large number of substances that did not fit into any of these categories. It can be concluded that for surveillance and official enforcement laboratories this will be the situation too – the full elucidation of all NIAS cannot be achieved to date using analytical chemistry alone.

The analytical approach would provide a useful demonstration of due diligence. However, it may need to be considered along with other complementary approaches. These could include concepts advocated elsewhere, such as toxicological evaluation of the whole migrate (if feasible) and/or threshold concepts such as threshold of regulation or thresholds of toxicological concern. However, all these would need to be formally assessed by the European Authorities to ensure the resulting combined evaluation approach is appropriate, scientifically sound and reliable.

The final report is available from the Agency’s Information Centre.
To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@foodstandards.gsi.gov.uk)

For any enquiries concerning this research project, please contact the relevant Programme contact or email: science@foodstandards.gsi.gov.uk