Small molecules called monomers are the building blocks of polymers, such as plastics, rubber, and silicones. Short chains made up of only a few monomers are called oligomers, and they are formed during the production and degradation of polymers. Recent scientific studies show that oligomers can migrate from food contact materials (FCMs) into food. However, not much is known yet about how exposure to these oligomers might affect our health.
Announced via a peer-reviewed scientific journal article in July 2022, research is underway by scientists in Switzerland, including from the Food Packaging Forum, to collect all the known exposure and hazard information for the oligomers that have been definitively identified migrating from polyethylene terephthalate (PET) FCMs. The new project will “identify and map areas of uncertainty and knowledge gaps in the hazard and exposure evidence-base for 34 PET oligomers [and] make recommendations for future research and chemical risk assessment activities, including toxicity testing and exposure assessments, to support regulatory decision-making.”
Within the research field, oligomers are defined to consist of 2 to 40 monomeric units and can be linear, branched or cyclic. They are formed as a result of either incomplete polymerization or subsequent degradation (thermal or hydrolytic) of polymeric material. The variety of possible oligomers constantly increases with the introduction of novel monomers and monomer combinations on the FCM market. Such a diversity, accompanied by the dearth of appropriate analytical standards, makes both qualitative and quantitative characterization of oligomeric migrants, as well as evaluation of their toxicity, a challenging task.
Detection, identification, and quantification of oligomers are best accomplished by liquid chromatography coupled with mass spectrometry (LC-MS) approaches. To ease identification, theoretical oligomer masses can be calculated from known monomer units. Safety assessment for oligomers has been traditionally based on the respective monomers, since physiological degradation of oligomers to monomers is assumed. However, polycondensate type cyclic oligomers may need to be considered separately; their susceptibility to hydrolysis in the gastrointestinal tract and their toxic properties are incompletely understood so far.
The tendency has been to consider oligomers within the broad group of non-intentionally added substances (NIAS). However, since oligomer chemistry is determined by a polymer manufacturing process, the authors of a 2016 scientific review paper published in the peer-reviewed journal Trends in Food Science & Technology, suggest to consider oligomers as a separate group of polymer-specific substances. The scientists from the Fraunhofer Institute for Process Engineering and Packaging IVV in Germany also provide in the study a comprehensive overview of oligomers potentially migrating from polymeric food contact materials (FCMs), covering their formation pathways, analytical methods, and migration data.
Despite the difficulty in identifying oligomers, research included in Food Packaging Forum’s FCCmigex database has found evidence from over 40 scientific studies of many oligomers migrating from different plastic polymers, silicones, and can coatings. Because of the difficulties and missing reference substances, there is not a lot of research on the effects of these oligomers on human health, though some have been found to potentially cause direct and indirect health effects (FPF reported, also here).
References
Schreier, V. et al. (2022). “Evaluating the food safety and risk assessment evidence-base of polyethylene terephthalate oligomers: Protocol for a systematic evidence map.” Environment International. DOI: 10.1016/j.envint.2022.107387
Hoppe, M. et al. (2016). “Identification and quantification of oligomers as potential migrants in plastics food contact materials with a focus on polycondensates – A review .” Trends in Food Science and Technology. DOI: 10.1016/j.tifs.2016.01.018
