Linear and cyclic oligomers in polybutylene terephthalate for food contact materials

Nano- and Microplastics Migration from Plastic Food Packaging into Dairy Products: Impact on Nutrient Digestion, Absorption, and Metabolism

The ongoing use of plastic polymers to manufacture food packaging has raised concerns about the presence of nano- and microplastics (NMPs) in a variety of foods. This review provides the most recent data on NMPs' migration from plastic packaging into dairy products. Also discussed are the possible effects of NMPs on nutrient digestion, absorption, and metabolism. Different kinds of dairy products, including skimmed milk, whole liquid milk, powder milk, and infant formula milk, have been found to contain NMPs of various sizes, shapes, and concentrations. NMPs may interact with proteins, carbohydrates, and fats and have a detrimental impact on how well these nutrients are digested and absorbed by the body. The presence of NMPs in the gastrointestinal tract may impact how lipids, proteins, glucose, iron, and energy are metabolized, increasing the risk of developing various health conditions. In addition to NMPs, plastic oligomers released from food packaging material have been found to migrate to various foods and food simulants, though information regarding their effect on human health is limited. Viewpoints on potential directions for future studies on NMPs and their impact on nutrient digestion, absorption, and health are also presented in this review.

Migration of oligomers from Tritan™ copolyester: application of hydrolysis for overall oligomer determination

Tritan™ (a kind of glycol-modified polycyclohexylene dimethylene terephthalate) is a novel copolyester mainly in use for the production of sports bottles and food storage containers. Oligomers in three food-grade Tritan™ samples were identified after dissolution-precipitation by high performance liquid chromatography with diode array detection and mass spectrometry and quantified after alkaline hydrolysis to the monomers. The obtained overall oligomer content <1000 Da determined by hydrolysis ranged from 7.2 to 10.6 mg/g material. Three consecutive migration experiments were performed according to the Commission Regulation (EU) No 10/2011. Oligomer migration values decreased from first to third migration during all simulations. Less than 25 µg/kg (third migrate) were detected in bottle migrates when tested under room temperature storage conditions (40 °C, 24 h) with simulants 3% acetic acid, 20 and 50% ethanol and during hot-fill testing (70 °C, 2 h) with simulants 3% acetic acid and 20% ethanol, respectively, while 170 µg/kg were determined in 50% ethanol after migration at 70 °C for 2 h. Food storage containers that were labelled as microwave-suitable by the supplier were tested according to the Joint Research Centre recommendations for microwave dishware. A strong deformation of the containers as well as a loss of transparency were observed during the tests (100 °C, 2 h with 10% ethanol and 3% acetic acid in an autoclave, 121 °C, 30 min with sunflower oil), questioning the suitability of the material for microwave applications. Maximum oligomer migration was 379 µg/kg during the third migration (sunflower oil at 121 °C for 30 min). Based on the migration data and an in silico oligomer evaluation according to the threshold of toxicological concern concept, no exceedances of daily thresholds for oligomers are expected from a proper use of Tritan™ drinking bottles, even with hot drinks.

Poly(ethylene terephthalate), Poly(butylene terephthalate), and Polystyrene Oligomers: Occurrence and Analysis in Food Contact Materials and Food

Polyesters (PES) and polystyrene (PS) are among the most used plastics in the production of food contact materials (FCM). The existence of compounds that could migrate from these materials into food requires a constant analytical control to ensure the safety of consumers due to consumption. It also implies a significant research challenge for their identification and quantification. One of the most important groups of known FCM migrants are the substances known as oligomers. PES and PS oligomers have long been suspected to possess some toxicological effects. The International Agency for Research on Cancer and the European Food Safety Authority alerted recently to the potential carcinogenicity of styrene, with its oligomers consequently being also in the spotlight. At the same time, PES cyclic oligomers are categorized as having Cramer III toxicity. Many recent works on the occurrence of poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), and PS oligomers in FCM and food have been published. The oligomeric chemical analysis requires the use of demanding analytical strategies to address their different physicochemical characteristics (melting points, octanol/water partition coefficients, and solubility properties). Chromatographic methods are normally preferred due to the intrinsic complexity of the target matrices, but the reduced amount of reliable analytical standards still hinders the widespread screening analysis of oligomers in food. This work presents the most relevant recent studies and analytical methodologies used in the analysis of PET, PBT, and PS oligomers in food and FCM, as well as current and future challenges.

Oligomers in polybutylene terephthalate for food contact-strategies on identification, quantification, and risk assessment

Oligomers are a significant group of migrating substances from food contact materials made of polyesters like polybutylene terephthalate (PBT). Twenty-three cyclic and linear oligomers with different end groups including olefin-terminated oligomers, which are associated with thermal stress of the material, were tentatively identified in PBT extracts by high-performance liquid chromatography with mass spectrometry and diode array detection. Quantification approaches based on chromophore concentration, relative response factors, and overall oligomer determination after hydrolysis to the monomer terephthalic acid were employed. An exhaustive extraction of thirteen PBT samples yielded an overall oligomer content of 1.87-6.10 mg/g material (sum of individual oligomers < 1,000 Da) with a predominant content of cyclic over linear oligomers. Migration experiments were performed according to Regulation (EU) No. 10/2011 using the official food simulants as well as cows' milk. A total of 218 µg cyclic oligomers/L milk were detected in the third migrate relevant for risk assessment of repeated-use articles under hot-fill conditions (70 °C, 2 h). The official food simulant for milk, 50% ethanol, was found to overestimate the actual migration into milk by a factor of four. Frying conditions using sunflower oil as the food simulant (200 °C, 10 min) resulted in a migration of 7.5 mg cyclic oligomers/kg oil. The exposure to migrating oligomers is critical in some scenarios when evaluated by the threshold of toxicological concern concept; however, the toxicological evaluation poses a challenge due to the possible hydrolysis of cyclic oligomers in the human gastrointestinal tract. Our experiments display 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.

Evaluating the food safety and risk assessment evidence-base of polyethylene terephthalate oligomers: Protocol for a systematic evidence map

BACKGROUND

Polyethylene terephthalate (PET) oligomers are ubiquitous in PET used in food contact applications. Consumer exposure by migration of PET oligomers into food and beverages is documented. However, no specific risk assessment framework or guidance for the safety evaluating of PET oligomers exist to date.

AIM

The aim of this systematic evidence map (SEM) is to identify and organize existing knowledge clusters and associated gaps in hazard and exposure information of PET oligomers. Research needs will be identified as an input for chemical risk assessment, and to support future toxicity testing strategies of PET oligomers and regulatory decision-making.

SEARCH STRATEGY AND ELIGIBILITY CRITERIA

Multiple bibliographic databases (incl. Embase, Medline, Scopus, and Web of Science Core Collection), chemistry databases (SciFinder-n, Reaxys), and gray literature sources will be searched, and the search results will be supplemented by backward and forward citation tracking on eligible records. The search will be based on a single-concept PET oligomer-focused strategy to ensure sensitive and unbiased coverage of all evidence related to hazard and exposure in a data-poor environment. A scoping exercise conducted during planning identified 34 relevant PET oligomers. Eligible work of any study type must include primary research data on at least one relevant PET oligomer with regard to exposure, health, or toxicological outcomes.

STUDY SELECTION

For indexed scientific literature, title and abstract screening will be performed by one reviewer. Selected studies will be screened in full-text by two independent reviewers. Gray literature will be screened by two independent reviewers for inclusion and exclusion.

STUDY QUALITY ASSESSMENT

Risk of bias analysis will not be conducted as part of this SEM.

DATA EXTRACTION AND CODING

Will be performed by one reviewer and peer-checked by a second reviewer for indexed scientific literature or by two independent reviewers for gray literature.

SYNTHESIS AND VISUALIZATION

The extracted and coded information will be synthesized in different formats, including narrative synthesis, tables, and heat maps.

SYSTEMATIC MAP PROTOCOL REGISTRY AND REGISTRATION NUMBER

Zenodo: https://doi.org/10.5281/zenodo.6224302.

Liquid chromatography-mass spectrometry method for the determination of polyethylene terephthalate and polybutylene terephthalate cyclic oligomers in blood samples

Food contact materials (FCM) polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) used extensively in food packaging may contain cyclic oligomers which may migrate into food and thus cause toxic effects on human health. A simple, fast, and sensitive ultra-high-performance liquid chromatography method quadrupole time-of-flight mass spectrometer was developed for the analysis of 7 cyclic oligomers in post-mortem blood samples. The targeted analytes were separated on a Waters BEH C18 (150 × 2.1 mm, 1.7 µm) analytical column by gradient elution. Calibration curves were constructed based on standard solutions and blood samples and Student's t-test was applied to evaluate the matrix effect. The LODs ranged from 1.7 to 16.7 μg mL^-1, while the method accuracy was assessed by recovery experiments and resulting within the range 84.2-114.6%. Such an analytical method for the determination of PET and PBT cyclic oligomers in biological samples is reported for the first time. The developed methodology allows the determination of these oligomers in blood providing a useful analytical tool to assess the exposure and thus the potential hazard and health risks associated with these non-intentionally added substances (NIAS) from PET and PBT FCM through food consumption. The method was validated and successfully applied to the analysis of 34 post-mortem whole blood samples. Polyethylene terephthalate trimer was detected in four of them, for the first time in literature.

Bio-based and compostable polyesters in food contact: analysis of monomers and (in)organic fillers

Polyesters labelled as bio-based or compostable are increasingly common among the 'bioplastics' in use as food contact materials (FCM). The knowledge of material composition is mandatory to predict potential leachable oligomers as well as to partly evaluate the correctness of the label 'bioplastic', which is used for promotional purposes. The composition of (bio)polyesters can be determined by alkaline hydrolysis of the entire material and subsequent analysis of the monomers via high-performance liquid chromatography with diode array detection and GC-MS detection. Thirty-three frequently used monomers (polycarboxylic acids, hydroxy carboxylic acids, polyols) including highly polar monomers such as lactic acid were analysed with detection limits below 10 g/kg of the material. Lactic acid enantiomer elucidation was performed using an enzyme assay. The content of non-hydrolysable residue was determined gravimetrically after hydrolysis, and the inorganic residue after washing. The composition of 12 polyesters mostly in food contact, labelled as bio-based or compostable and sampled from the market was elucidated recovering 92-101% of the total mass by summing up the determined monomers and non-polyester contents. Seven different monomers were detected in the 12 samples (up to four different monomers per sample), lactic acid being the most common (9 samples) with contents ranging from a minor component (about 11 mol%) up to the only monomer found in the material. The ratio of d- to l-lactic acid ranged from 0.3:99.7 to 4.7:95.3 (w/w). The non-hydrolysable (in)organic residue was quantified in amounts of up to 390 g/kg. Overall, the presented analytical protocol is a fundamental tool helping both to verify the appropriateness of labelling as biopolyesters as well as to predict potential leachables such as oligomers during an FCM risk assessment.

Safety of Plastic Food Packaging: The Challenges about Non-Intentionally Added Substances (NIAS) Discovery, Identification and Risk Assessment

Several food contact materials (FCMs) contain non-intentionally added substances (NIAS), and most of the substances that migrate from plastic food packaging are unknown. This review aimed to situate the main challenges involving unknown NIAS in plastic food packaging in terms of identification, migration tests, prediction, sample preparation, determination methods and risk assessment trials. Most studies have identified NIAS in plastic materials as polyurethane adhesives (PU), polyethylene terephthalate (PET), polyester coatings, polypropylene materials (PP), multilayers materials, plastic films, polyvinyl chloride (PVC), recycled materials, high-density polyethylene (HDPE) and low-density polyethylene (LDPE). Degradation products are almost the primary source of NIAS in plastic FCMs, most from antioxidants as Irganox 1010 and Irgafos 168, following by oligomers and side reaction products. The NIAS assessment in plastics FCMs is usually made by migration tests under worst-case conditions using food simulants. For predicted NIAS, targeted analytical methods are applied using GC-MS based methods for volatile NIAS and GC-MS and LC-MS based methods for semi- and non-volatile NIAS; non-targeted methods to analyze unknown NIAS in plastic FCMs are applied using GC and LC techniques combined with QTOF mass spectrometry (HRMS). In terms of NIAS risk assessment and prioritization, the threshold of toxicological concern (TTC) concept is the most applied tool for risk assessment. Bioassays with sensitive analytical techniques seem to be an efficient method to identify NIAS and their hazard to human exposure; the combination of genotoxicity testing with analytical chemistry could allow the Cramer class III TTC application to prioritize unknown NIAS. The scientific justification for implementing a molecular weight-based cut-off (<1000 Da) in the risk assessment of FCMs should be reevaluated. Although official guides and opinions are being issued on the subject, the whole chain's alignment is needed, and more specific legislation on the steps to follow to get along with NIAS.

Analysis of PBT and PET cyclic oligomers in extracts of coffee capsules and food simulants by a HPLC-UV/FLD method

A HPLC-UV/FLD method was validated for the quantification of six polyethylene terephthalate (PET) and four polybutylene terephthalate (PBT) oligomers. PBT oligomers are EU regulated, while the PET ones are considered non-intentionally added substances (NIAS). LOQs were higher than 0.4 and 3.5 μg kg-1 for the simulants and in the polymer extracts, respectively. Recoveries ranged from 95 to 114 % with RSDs below 12%. Migration testing of PBT and polypropylene coffee capsules were performed with H2O and simulant C, and extracts were obtained with accelerated solvent extraction (ASE). For the latter legislative limits weren't surpassed. As no migration limits are existing for the analytes, both EFSA's toxicological threshold of concern (TTC) and sum of oligomers approaches were applied. The majority of oligomers were below the TTC (90 µg/person/day), but the limit value of 50 µg/kg food was surpassed for some capsules, which indicates a significant intake in both single and multiple consumption.

Development and validation of an UHPLC-qTOF-MS method for the quantification of cyclic polyesters oligomers in pasta by applying a modified QuEChERS clean-up

An Ultra High-Performance Liquid chromatography method quadruple time-of-flight mass spectrometry has been developed for the analysis of 11 cyclic polyesters oligomers, following a modified QuEChERS clean-up with alumina/primary secondary amine, in pasta. Target analytes were polyethylene terephthalate (PET) 1^st series cyclic dimer to heptamer, polybutylene terephthalate (PBT) dimer to pentamer and a polyurethane oligomer. Standard addition method was applied for the calibration, and the limits of quantification ranged from 3.2 to 17.2 ng g^-1. Recoveries ranged from 86.4 to 109.8%, RSDs were lower than 12% for all analytes, and matrix effect never exceeded ± 2.5%. The method was successfully applied to real commercial pasta samples, where the PET 1^st series cyclic trimer was the most abundant oligomer, being found in all tested samples. The 1^st series PET cyclic dimer and tetramer, as well as 1,4,7-trioxacyclotridecane-8,13-dione, were found in considerable amounts. Traces of the 2^nd and 3^rd series PET cyclic dimers were also found.

Characterisation, release and migration of phenolic compounds from resoles used in polyester-phenol coatings intended for food contact materials

Resoles are multifarious pre-polymeric resins produced by the condensation of basic chemicals phenols, formaldehyde and optionally aliphatic alcohols like butanol. They are widely used as cross-linkers to form resistant internal coatings on metal surfaces of cans, containers or closures. Although the application of resoles is common in food contact, usually little is known about their exact composition, the toxicological hazards of their individual constituents and the migration of phenolic compounds, e.g., of the potentially endocrine-disrupting chemical bisphenol F. Our study fills major gaps of knowledge in risk assessment, using the example of a two-layer polyester-phenol coating system, which is based on three different resoles and is commercially used for closures of infant food glass jars. Various analytical approaches, namely size-exclusion chromatography, nuclear magnetic resonance spectroscopy, liquid chromatography coupled to mass spectrometry, fluorescence and diode array detection as well as gas chromatography-mass spectrometry were evaluated to quantitatively characterise resoles. Additionally, derivatisation with dansyl chloride as well as Folin-Ciocalteu colorimetric assay was adapted first times to determine the total phenol content from technical resoles. Individual mono- and bisphenols were determined in resoles up to about 120 mg/g, while the concentration of bisphenol F isomers was below 10 mg/g. Migration from the coating system was determined after sterilisation (121°C, 1 h, 20% ethanol). Results were ~2 µg/dm2 for identified individual mono-phenols like 2-hydroxybenzyl alcohol and up to ~120 µg/dm2 for total phenolic compounds, representing approximately 7% of the overall migration. The migration of bisphenol F isomers was negligible below 0.3 µg/dm2. Potential exposure to migrating phenols was assessed based on the threshold of toxicological concern concept to be significantly below for individual phenols and in the same order of magnitude for total phenols compared to the respective thresholds calculated for infants.

Proficiency test on the determination of polyethylene and polybutylene terephthalate cyclic oligomers in a food simulant

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Migration of food contact material substances.

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Mass fractions of PET and PBT cyclic dimers/trimers in food simulant D1.

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First proficiency test on polyester oligomers.

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Validation of analytical method.

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Assessment of analytical capabilities of EU NRLs and OCLs.

The outcome of a proficiency test (PT) organised by the European Union Reference Laboratory for Food Contact Materials (EURL-FCM) is presented. The PT was set up to assess the analytical performance of National Reference Laboratories (NRLs) and Official Control Laboratories (OCLs) in the determination of mass fractions of polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) cyclic dimers and trimers in the official food simulant D1 containing ethanol and water (50:50 v/v).

The EURL-FCM had developed and validated an analytical method based on HPLC-UV to monitor the homogeneity and stability of the target oligomers in the PT test items and to determine the respective assigned values, as prescribed in ISO 17043, 2010ISO 17043, 2010. The standard operating procedure of the method was provided to the participants and could be used instead of their own routine methods. Laboratory results were rated using z, z' and ζ scores in accordance with ISO 13528, 2015. The standard deviation for proficiency assessment, σ_pt, was set to 20 % of the respective assigned value, for all the four studied oligomers, based on the perception of experts.

A total of 36 participants from 26 countries have registered to the exercise. They received two test items. Solution 1 consisted of food simulant D1 fortified with a known mass fraction of the four oligomers, while Solution 2 was obtained by a migration experiment with PET bottles and food simulant D1 and further fortification of the resulting solution with the four oligomers.

The majority of the participating laboratories presented satisfactory results for the four PET and PBT oligomers. For the analysis of Solution 1, 79–88 % of the participants obtained |z (or z')-scores| below 2, while the satisfactory performances ranged from 71 to 85 % for Solution 2. This PT has been organised for the first time at EU level for the analysis of polyester oligomers and confirms that most of the NRLs are able to monitor properly these oligomers in the frame of Regulation (EU) No 10/2011.

Quantification of PET cyclic and linear oligomers in teabags by a validated LC-MS method - In silico toxicity assessment and consumer's exposure

Determination of polyethylene terephthalate (PET) dimer up to heptamer 1st series cyclic oligomers, applying an LC-qTOF-MS method, has been developed and validated. Recoveries ranged between 80 and 112% with RSDs lower than 15%. An innovative semi-quantitative approach has been applied for 2nd and 3rd series cyclic oligomers, using the closest structural-similar 1st series cyclic oligomer standard as analytical reference. Oligomers from the three series were quantified in PET teabags after migration experiments with water and food simulants C (20% v/v ethanol in water) and D1 (50% v/v ethanol in water). No legal migration limits exist currently for these substances. In silico genotoxicity assessment of all identified oligomers has been performed and showed no genotoxicity alert for linear or cyclic molecules. Exposure assessment was performed using EFSA's approach on the total sum of migrating oligomers and on toxicological threshold-of-concern. Amounts found in water were in some cases significantly higher than the respective limits, especially in the worst-case scenario of multiple consumption.

Assessment of the Impact of Accelerated Migration Testing for Coated Food Cans Using Food Simulants

In this study, an accelerated migration test on food can coatings into food simulants was investigated. Food simulants covering a wide range of polarity were used to conduct migration tests at 60 °C with storage times ranging from 4 h to 30 days. Epoxy-resins, acrylic-phenolic, polyester, and vinyl coatings were exposed to water, 3% acetic acid, 50% ethanol, and Miglyol 812®. Using liquid chromatography coupled to a variety of detectors (UHPLC-Q-Orbitrap-MS, UFLC-MS/MS, and HPLC-DAD), migration of several monomers and previously identified oligomers, as well as some unidentified migrants, were determined during the experiment. The data from this study was compared to our findings from previous long-term migration studies with storage times ranging from 24 h to 540 days at 40 °C using the same can coating applications. The results illustrate that performing migration experiments for short time periods at 60 °C may mimic migration results that would be obtained at 40 °C after long-term migration tests (up to 1.5 years) from food can coatings into food simulants.

Release and migration of cyclic polyester oligomers from bisphenol A non-intent polyester-phenol-coatings into food simulants and infant food - a comprehensive study

Coatings for cans or closures are essential to protect the metal from corrosion and the food from migration of hazardous metal ions. Since coatings are no inert materials, they can release substances of potential health concern into food. In the present study, a comprehensive analysis is presented for a complex two-layered polyester-phenol-coating commercially used for metal closures of complementary infant food in sterilised glass jars. Focussed on the identity and migration of cyclic polyester oligomers as a kind of predictable non-intentionally added substances, polyester resin raw materials (n = 3) as well as individual coating layers (n = 3) were characterised by several analytical strategies (size exclusion chromatography, high-performance liquid chromatography mass spectrometry, diode array detection, charged aerosol detection, monomer determination after alkaline hydrolysis, overall migrate). The main polyester monomers were terephthalic acid, isophthalic acid, trimellitic acid, ethylene glycol, diethylene glycol, neopentylglycol, 2-methyl-1,3-propanediol, 1,4-butanediol and tricyclodecanedimethanol. The coatings were extracted with solvents acetonitrile and ethanol (24 h, 60°C), food simulants 50% ethanol, 20% ethanol and water (1 h, 121°C) as well as homemade and commercial baby food (1 h, 121°C). The released total polyester content determined by alkaline hydrolysis ranged from 288 µg/dm² (water, 1 h, 121°C) to 6154 µg/dm² (acetonitrile, 24 h, 60°C). However, individual cyclic oligomers, mainly dimers, were released from the coating to up to about 140 µg/dm². Migration into infant food was best represented by the food simulants water (up to 1% fat) and 20% ethanol (up to 5% fat). Cyclic polyester oligomers are classified as Cramer III substances by the threshold of toxicological concern concept associated to an exposure threshold of 1.5 µg/kg body weight per day. Exposure to cyclic polyester oligomers might be a potential concern for highly exposed infants.

Oligomers in polyethylene furanoate - identification and quantification approach via LC-UV LC-MS response ratio

Polyethylene furanoate polymer is intended to be used as a food contact material. A PEF polymer sample was investigated for its oligomer composition by solvent extraction and using HRLC-MS. The 20 oligomers found were divided into four groups: group I contains cyclic oligomers consisting of furandicarboxylic acid and monoethylene glycol units, group II comprises cyclic oligomers consisting of furandicarboxylic acid, monoethylene glycol units and one diethylene glycol unit, group III are cyclic oligomers were two monoethylene glycol units are substituted by diethylene glycol units and group IV are linear oligomers consisting of furandicarboxylic acid and monoethylene glycol units. Oligomers of group I account for around 87% of the total oligomer content, group II oligomers 12% and group III oligomers 1%. The contribution of group IV oligomers is very small: less than 0.05%. MS-MS experiments showed similar fragmentation patterns for all oligomers. The results of this study demonstrate that oligomers are abundant in the PEF material and are potential migrants to foods that are in contact with the polymer. Oligomers of group I and group II have the same absorption maxima in UV detection which was used to develop a quantification approach for these oligomers using dimethyl 2,5-furandicarboxylate as external standard.