Oligomers can form as a side product during the polymerization or by the degradation of the (final) polymeric material and are one type of non-intentionally added substance (NIAS) that may be present in plastic food contact materials (FCMs). In an article published on July 9, 2023, in the journal Foods, Dimitra Diamantidou from the Aristotle University of Thessaloniki, Greece, and co-authors analyzed the migration of cyclic polyethylene terephthalate (PET) oligomers from four virgin and recycled PET bottles. Since bottles were intended for use in contact with edible oils and beverages they performed migration experiments in 95% ethanol for 10 days at 60 °C as well as storing virgin olive oil in them for one and a half years.
Using ultra-high-pressure liquid chromatography quadruple time-of-flight mass spectrometry (UHPLC-qTOF-MS), the researchers detected no PET oligomers in the olive oil samples. However, in the food simulant PET dimer levels ranged between 38.8 to 198 µg/L, PET trimers between 587 to 2950 µg/L , and PET tetramers between 0.51 and 9.32 µg/L. Generally, “migration from recycled PET was more than doubled compared to virgin PET bottles” and PET pentamers were only detected in migrates of recycled PET. The authors hypothesized that “the production technology could be crucial for the safety characteristics of recycled PET bottles.” Besides cyclic oligomers, they further tentatively identified their linear derivatives.
In a previous study, Diamantidou found PET oligomers to be present in post-mortem blood samples (FPF reported). In May 2023, scientists from several institutions including the Food Packaging Forum mapped the available research on hazards and exposure of 34 oligomers in PET for food contact and pointed out the crucial knowledge gaps concerning the safety of PET oligomers (FPF reported).
On July 01, 2023, Adriana C. Mârşolea and co-authors from the University Politehnica of Bucharest, Romania, reported in the International Journal of Food Science & Technology that bisphenol A (BPA) can also migrate from PET bottles and related the presence of BPA and its migration to cross-contamination during recycling. BPA has also been found to migrate from TritanTM bottles (FPF reported) which are usually considered BPA-free. TritanTM is a glycol-modified polycyclohexylene dimethylene terephthalate that hit the market as a replacement for polycarbonate and was initially mostly used for reusable sports bottles.
In an article published on July 25, 2023, in the journal Food Additives & Contaminants: Part A, Marie Kubicova and co-authors from the Technical University Dresden, Germany, were interested in the migration of oligomers from TritanTM.
The researchers purchased TritanTM pellets, drinking bottles, and microwaveable, machine washable, and freezable storage containers in Germany and performed extraction and migration experiments under different conditions. To test for migration, they used ethanol (10, 20, 50, and 95%) and acetic acid 3% as food simulants and sunflower oil according to EC Regulation (EU) No 10/2011 and repeated each experiment three times. Migrates were applied to high performance liquid chromatography with a diode array detector (HPLC-DAD) to assess oligomer concentrations. The microwaveable containers were tested as recommended by the European Commission Joint Research Center for such dishware.
The authors reported that 170 µg oligomers/kg migrated from the bottles at 70 °C for 3 h in 50% ethanol, whereas for the other conditions, concentrations were below 25 µg/L. Generally, the level of oligomers decreased with the number of consecutive migrations. Microwave dishware deformed and lost its transparency “questioning the suitability of the material for microwave applications.” Oligomer migration reached a maximum at the third migration into sunflower oil at 121 °C and 30 min of 379 mg/kg.
The scientists also assessed the risk of TritanTM oligomers using the threshold of toxicological concern (TCC) concept. Here, they found that “the amount of released oligomers should not exceed the TCC thresholds under foreseeable conditions of use” of the drinking bottles. However, “storage containers made of TritanTM were proven to be non-suitable for heating of food above 100 °C due to a deformation of the material.”
Kubicova and co-authors have previously assessed the migration of polybutylene terephthalate (PBT) oligomers from food contact articles and reported that human exposure to oligomers can exceed the daily threshold in certain scenarios (FPF reported). A review published earlier in 2023 summarized the presence of several types of oligomers in FCMs and food while also looking into their toxicity (FPF reported).
References
Diamantidou, D. et al. (2023). “Analysis of Migrant Cyclic PET Oligomers in Olive Oil and Food Simulants Using UHPLC-qTOF-MS.” Foods. DOI: 10.3390/foods12142739
Kubicova, M. et al. (2023). “Migration of oligomers from Tritan™ copolyester: application of hydrolysis for overall oligomer determination.” Food Additives & Contaminants: Part A. DOI: 10.1080/19440049.2023.2232244
Mârşolea, A. C. et al. (2023). “Migration and leaching behaviour of Bisphenol A from polyethylene terephthalate water bottles under different storage conditions.” International Journal of Food Science & Technology. DOI: 10.1111/ijfs.16583
