Researchers analyze oligomer in extracts and migrates of polybutylene terephthalate (PBT) food contact articles also comparing levels in food and food simulants; report human exposure to oligomers can exceed daily threshold in some scenarios; express the need for toxicological evaluation of PBT oligomers.
Polybutylene terephthalate (PBT), is a polyester that is used for kitchen utensils and other repeat-use food contact articles. During the production of the polymer, linear and cyclic oligomers can be formed as by-products (i.e., non-intentionally added substances, NIAS) which are present in PBT-based products. In an article published on October 7, 2022, in the journal Food Additives & Contaminants: Part A, Marie Kubicova and co-authors from the Technical University Dresden, Germany, studied linear and cyclic oligomers in PBT food contact articles, their migration potential, and exposure. Oligomer identification and quantification were conducted using liquid chromatography-mass spectrometry-based analytical procedures.
The scientists obtained 15 food-grade PBT samples (pellets and articles) from five suppliers in the European Union between 2017 and 2020. For extraction experiments, the samples were cut and milled before treatment with dichloromethane for 3h ultrasonication. For migration experiments, cut or uncut utensils were incubated in food (sunflower oil and milk) or food simulants (20%, 50%, and 95% ethanol, 3% acetic acid) at different temperatures and durations according to regulation for plastic food contact materials EC 10/2011.
Kubicova and co-authors reported that in exhaustive extracts of the PBT samples 1.87-6.10 mg oligomers/g material were present, with cyclic exceeding linear oligomers. Depending on the PBT, a different pattern of oligomers was observed which the authors “connected to the different manufacturing processes.” 218 µg cyclic oligomers/L milk were detected upon repeated migration (3x), which is relevant for assessing the risk of repeated-use articles, at 70°C for 2 hours. The simulation of frying conditions using sunflower oil at 200° C for 10 min “resulted in a migration of 7.5mg cyclic oligomers/kg oil.”
The scientists also compared the migration levels in food simulants and food. Here, they found that migration in 50% ethanol, which is the official food simulant for milk, leads to a four-times higher migration compared to milk. Using the threshold of toxicological concern (TCC) concept and evaluating cyclic oligomers as Cramer III substances (worst-case scenario) showed that the exposure can exceed the daily threshold of 90 µg, e.g., when consuming two cups of hot milk in PBT. Assuming a best-case scenario, of all migrating oligomers being linear, showed that the Cramer I threshold (1800 mg/day) would probably not be exceeded.
Based on their study outcomes the authors expressed the need “for a toxicological evaluation of PBT oligomers because the migration of cyclic oligomers is expected to exceed the current in silico–based thresholds under foreseeable conditions of use.”
A previous study also analyzed oligomer migration from PBT and considered it safe based on threshold of toxicological concern considerations (FPF reported). Not only from PBT but also from other types of food packaging the migration of oligomers was studied (FPF reported). An ongoing project is evaluating the food safety and risk assessment evidence-base of PET oligomers (see here).