Genotoxicity of styrene oligomers extracted from polystyrene intended for use in contact with food

Biomarkers of oxidative stress, inflammation, and genotoxicity to assess exposure to micro- and nanoplastics. A literature review

The increased awareness about possible health effects arising from micro- and nanoplastics (MNPs) pollution is driving a huge amount of studies. Many international efforts are in place to better understand and characterize the hazard of MNPs present in the environment. The literature search was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology in two different databases (PubMed and Embase). The selection of articles was carried out blind, screening titles and abstracts according to inclusion and exclusion criteria. In general, these studies rely on the methodology already in use for assessing hazard from nanomaterials and particles of concern. However, only a limited number of studies have so far directly measured human exposure to MNPs and examined the relationship between such exposure and its impact on human health. This review aims to provide an overview of the current state of research on biomarkers of oxidative stress, inflammation, and genotoxicity that have been explored in relation to MNPs exposure, using human, cellular, animal, and plant models. Both in-vitro and in-vivo models suggest an increased level of oxidative stress and inflammation as the main mechanism of action (MOA) leading to adverse effects such as chronic inflammation, immunotoxicity and genotoxicity. With the identification of such biological endpoints, representing critical key initiating events (KIEs) towards adaptive or adverse outcomes, it is possible to identify a panel of surrogate biomarkers to be applied and validated especially in occupational settings, where higher levels of exposure may occur.

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.

Single and combined potential of polystyrene microparticles and fluoranthene in the induction of DNA damage in haemocytes of Mediterranean mussel (Mytilus galloprovincialis)

In this study, the possible 'vector effect' within the exposure of Mediterranean mussels (Mytilus galloprovincialis) to polystyrene microplastics with adsorbed fluoranthene was investigated by applying the multibiomarker approach. The major focus was placed on genotoxicological endpoints as to our knowledge there are no literature data on the genotoxicity of polystyrene microparticles alone or with adsorbed fluoranthene in the selected experimental organisms. DNA damage was assessed in haemocytes by comet assay and micronucleus test. For the assessment of neurotoxicity, acetylcholinesterase activity was measured in gills. Glutathione S-transferase was assessed in gills and hepatopancreas since these enzymes are induced for biotransformation and excretion of lipophilic compounds such as hydrocarbons. Finally, differences in physiological response within the exposure to polystyrene particles, fluoranthene, or particles with adsorbed fluoranthene were assessed by the variation of heart rate patterns studied by the noninvasive laser fibre-optic method. The uniform response of individual biomarkers within the exposure groups was not recorded. There was no clear pattern in variation of acetylcholinesterase or glutathione S-transferase activity which could be attributed to the treatment. Exposure to polystyrene increased DNA damage which was detected by the comet assay but was not confirmed by micronucleus formation. Data of genotoxicity assays indicated differential responses among the groups exposed to fluoranthene alone and fluoranthene adsorbed to polystyrene. Change in the heart rate patterns within the studied groups supports the concept of the Trojan horse effect within the exposure to polystyrene particles with adsorbed fluoranthene.

Migration of styrene oligomers from food contact materials: in silico prediction of possible genotoxicity

Styrene oligomers (SO) are well-known side products formed during styrene polymerization. They consist mainly of dimers (SD) and trimers (ST) that have been shown to be still residual in polystyrene (PS) materials. In this study migration of SO from PS into sunflower oil at temperatures between 5 and 70 °C and contact times between 0.5 h and 10 days was investigated. In addition, the contents of SD and ST in the fatty foodstuffs créme fraiche and coffee cream, which are typically enwrapped in PS, were measured and the amounts detected (of up to 0.123 mg/kg food) were compared to literature data. From this comparison, it became evident, that the levels of SO migrating from PS packaging into real food call for a comprehensive risk assessment. As a first step towards this direction, possible genotoxicity has to be addressed. Due to technical and experimental limitations, however, the few existing in vitro tests available are unsuited to provide a clear picture. In order to reduce uncertainty of these in vitro tests, four different knowledge and statistics-based in silico tools were applied to such SO that are known to migrate into food. Except for SD4 all evaluated SD and ST showed no alert for genotoxicity. For SD4, either the predictions were inconclusive or the substance was assigned as being out of the chemical space (out of domain) of the respective in silico tool. Therefore, the absence of genotoxicity of SD4 requires additional experimental proof. Apart from SD4, in silico studies supported the limited in vitro data that indicated the absence of genotoxicity of SO. In conclusion, the overall migration of all SO together into food of up to 50 µg/kg does not raise any health concerns, given the currently available in silico and in vitro data.

Styrene-acrylonitrile-copolymer and acrylonitrile-butadiene-styrene-copolymer: a study on extractable and migratable oligomers

Styrene-acrylonitrile-copolymer (SAN) and acrylonitrile-butadiene-styrene-copolymer (ABS) are gaining in importance as food contact materials. Oligomers and other non-intentionally added substances can migrate into foodstuffs. Five SAN and four ABS samples from the German market and manufacturers were extracted and the extractable oligomers were characterised by high performance liquid chromatography-mass spectrometry/ultraviolet detection/chemiluminescence nitrogen detection/fluorescence detection and gas chromatography-mass spectrometry. Trimers, formed from acrylonitrile and styrene units, were determined to be the dominating group of extractable oligomers in SAN and ABS in concentrations of about 4900-15800 mg/kg material. Furthermore, styrene-acrylonitrile dimers, styrene oligomers, styrene monomer and ethylbenzene were identified in the sample extracts. Migration testing with three consecutive migrations for multiple use articles was performed for two SAN articles. Migration of trimers into water, 3% acetic acid, 10% and 20% ethanol under hot-fill conditions (70°C, 2 h) was not detectable above 9 µg/dm², while 50% ethanol acting as a food simulant for milk (124 µg/dm² trimers during the third migration) was shown to overestimate the actual migration into milk (< 11 µg/dm² trimers at 70°C, 2 h). 2-Amino-3-methyl-1-naphthalenecarbonitrile (AMNC), an oligomer degradation product and a primary aromatic amine, was detected in all material sample extracts (0.3-17.1 mg/kg material) and was released into food simulants in low amounts (< 0.014 µg/dm² during the third migration into 50% ethanol at 70°C, 2 h).

Diffusion Coefficients and Activation Energies of Diffusion of Organic Molecules in Polystyrene below and above Glass Transition Temperature

General Purpose Polystyrene (GPPS) and High Impact Polystyrene (HIPS) is used in packaging food as well as for technical products. Knowledge of the diffusion behavior of organic molecules in polystyrene (PS) is important for the evaluation of the diffusion and migration process. Within this study, diffusion coefficients were determined in GPPS and HIPS below and above the glass transition temperature. Diffusion coefficients were determined from desorption kinetics into the gas phase using spiked GPPS and HIPS sheets as well as from permeation kinetics through a thin GPPS film. Overall, 187 diffusion coefficients were determined in GPPS and HIPS at temperatures between 0 °C and 115 °C. From the temperature dependency of the diffusion coefficients 45 activation energies of diffusion E_A and the pre-exponential factor D₀ were determined. As expected, the activation energies of diffusion E_A show a strong dependency from the molecular volume of the investigated substances. At the glass transition temperature, only a slight change of the diffusion behavior were observed. Based on E_A and D₀, prediction parameters for diffusion coefficients were established.

Risk Assessment of Food Contact Materials

Food contact materials (FCM) can contain chemicals that could migrate from the material itself to the foodstuff posing health concerns if ingested in non-safe quantities by the consumer. FCM include containers, packaging, machinery or kitchenware and can be made from different materials like plastics, paper and board, metal or glass. Printing inks are also an important part of FCM. FCM have an important role in preventing damage or spoilage of the foodstuff and are essential along the food chain. Therefore, their safety needs to be carefully assessed in order to reduce the exposure to potentially hazardous substances and protect the health of the consumer. At the EU level, the legislation on FCM establishes general safety requirements for FCM. In addition, for certain materials, specific measures concerning usage and release of substances have been set. For materials or articles not specifically regulated in this harmonised framework, safety must be proven on a case-by-case basis. National legislations and lists of substances evaluated by competent authorities are important data sources in this context. One of the most important databases are the 'BfR Recommendations on Food Contact Materials' and the soon to come German national regulation on printing inks. BfR Unit 74, besides dealing with chemical risk assessment of FCM, is responsible for the evaluation of application dossiers for including substances into the BfR recommendations on FCM or the substance list of the printing inks regulation. Through the proposed work programme the fellow has been involved in risk assessment of substances that migrate from FCM into foodstuff gaining experience in the methodologies used to perform the scientific data evaluation as well as to support the BfR Unit 74s work.

Development and validation of a fast gas chromatography mass spectrometry method for the quantification of selected non-intentionally added substances and polystyrene/polyurethane oligomers in liquid food simulants

A simple, fast, sensitive and reliable method was developed for the simultaneous determination of 13 food contact materials (FCM) regulated substances and non-intentionally added substances (NIAS) migrating into official food simulants. The method has been optimized to quantify the monomers styrene and α-methyl styrene, selected polystyrene oligomers (dimers, trimers) and polyester urethane-based oligomers (PU) cyclic oligomers, as well as cyclic NIAS originating from food packaging such as 2,6-Di-tert-butylbenzoquinone and 7,9-Di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione. The method employs liquid-liquid extraction of aqueous ethanol food simulants with dichloromethane, and analysis with gas chromatography coupled to mass spectrometry (GC-MS) with a total analysis time of less than 16 min, with limits of detections ranging from 0.32 ng mL^-1 (1,1-diphenyl-ethylene) to 14.8 ng mL^-1 for 7,9-di-tert-butyl-1-oxaspiro[4.5]deca-6,9-diene-2,8-dione and respective limits of quantification from 1.0 ng mL^-1 to 41.7 ng mL^-1, for the same analytes. Accuracy and precision results showed that the method is sufficiently accurate for all target analytes, with recoveries ranging between 80 and 110% and relative standard deviations (RSDs) smaller than 16% at the three selected concentration levels. The method has been successfully applied to seven FCM. Results indicated that significant amounts of polystyrene monomers, dimers and trimers are migrating into food simulants; this is also the case for polyester urethane-based oligomers (PU). Exposure assessment estimation was performed using EFSA's approach on the total sum of migrating oligomers. In certain cases, amounts of PS and PU oligomers found to be in some cases higher than the respective limits, for the sum of oligomers with a MW lower than 1000 Da.

Evaluation of the Suitability of Mammalian In Vitro Assays to Assess the Genotoxic Potential of Food Contact Materials

Background: Non-targeted screening of food contact materials (FCM) for non-intentionally added substances (NIAS) reveals a great number of unknown and unidentified substances present at low concentrations. In the absence of toxicological data, the application of the threshold of toxicological concern (TTC) or of EU Regulation 10/2011 requires methods able to fulfill safety threshold criteria. In this review, mammalian in vitro genotoxicity assays are analyzed for their ability to detect DNA-damaging substances at limits of biological detection (LOBD) corresponding to the appropriate safety thresholds. Results: The ability of the assays to detect genotoxic effects varies greatly between substance classes. Especially for direct-acting mutagens, the assays lacked the ability to detect most DNA reactive substances below the threshold of 10 ppb, making them unsuitable to pick up potential genotoxicants present in FCM migrates. However, suitability for the detection of chromosomal damage or investigation of other modes of action makes them a complementary tool as part of a standard test battery aimed at giving additional information to ensure safety. Conclusion: improvements are necessary to comply with regulatory thresholds to consider mammalian genotoxicity in vitro assays to assess FCM safety.

Value and limitation of in vitro bioassays to support the application of the threshold of toxicological concern to prioritise unidentified chemicals in food contact materials

Some of the chemicals in materials used for packaging food may leak into the food, resulting in human exposure. These include so-called Non-intentionally Added Substances (NIAS), many of them being unidentified and toxicologically uncharacterized. This raises the question of how to address their safety. An approach consisting of identification and toxicologically testing all of them appears neither feasible nor necessary. Instead, it has been proposed to use the threshold of toxicological concern (TTC) Cramer class III to prioritise unknown NIAS on which further safety investigations should focus. Use of the Cramer class III TTC for this purpose would be appropriate if amongst others sufficient evidence were available that the unknown chemicals were not acetylcholinesterase inhibitors or direct DNA-reactive mutagens. While knowledge of the material and analytical chemistry may efficiently address the first concern, the second could not be addressed in this way. An alternative would be use of a bioassay capable of detecting DNA-reactive mutagens at very low levels. No fully satisfactory bioassay was identified. The Ames test appeared the most suitable since it specifically detects DNA-reactive mutagens and the limit of biological detection of highly potent genotoxic carcinogens is low. It is proposed that for a specific migrate, the evidence for absence of mutagenicity based on the Ames test, together with analytical chemistry and information on packaging manufacture could allow application of the Cramer class III TTC to prioritise unknown NIAS. Recommendations, as well as research proposals, have been developed on sample preparation and bioassay improvement with the ultimate aim of improving limits of biological detection of mutagens. Although research is still necessary, the proposed approach should bring significant benefits over the current practices used for safety evaluation of food contact materials.

Mutagenicity assessment of food contact material migrates with the Ames MPF assay

A major challenge in the safety assessment of food contact materials (FCM) is the evaluation of unknown non-intentionally added substances (NIAS). Even though consumer exposure levels may be quantitatively low, these substances are considered to be of high toxicological concern if they act as DNA reactive mutagens. From a safety assessment perspective, it is therefore important to detect their presence in FCM migrates. The present study applied the Ames MPF assay to assess the mutagenicity of migrates obtained from 30 food contact material samples out of 3 categories: plastics, composite materials and coatings. As a food simulant, 95% ethanol (EtOH) had a superior performance to less volatile simulants when evaluating recovery rates of representative model substances in different volatility categories. To monitor possible interference of the FCM matrix with Ames MPF results, migrates were spiked with reference substances and recovery rates were established. Out of 30 samples tested, two caused significant inhibition of revertant formation in the presence of the spiking control. Overall detection limits of the applied test method were estimated by determination of the lowest effective concentrations (LEC) for 10 Ames-positive substances. Even though the current limits of detection are not sufficient to entirely fulfil regulatory and safety requirements, three out of 30 FCMs showed evidence of dose-dependent effects in the Ames MPF assay. Overall, the data obtained supported the relevance of testing FCM migrates for DNA reactive contaminants and showed the value of the Ames MPF assay for the safety assessment of FCMs.

Suitability of the Ames test to characterise genotoxicity of food contact material migrates

Non-intentionally added substances (NIAS) are chemical impurities which can migrate from packaging materials (FCM) into food. Safety assessment of NIAS is required by European law, but currently there is no comprehensive testing strategy available. In this context, one key element is to get insight on the potential presence of genotoxic NIAS in FCM migrates. This raises questions about the limit at which genotoxins can be detected in complex mixtures such as FCM migrates, and if such limits of detection (LOD) would be compatible with safety. In this context, the present review assesses the suitability of the Ames assay to address genotoxicity of FCM migrates. Lowest effective concentrations of packaging-related and other chemicals in test media were retrieved from scientific literature and used as surrogates of LODs to be benchmarked against a value of 0.01 mg kg^-1 (10 ppb) in migrates. This is a pragmatic threshold used in FCM safety evaluation to prioritise substances requiring proper identification and risk assessment. The analysis of the data shows that only potent genotoxins can theoretically be detectable at a level of 0.01 mg kg^-1 in migrates or food. Only a minority (10%) of genotoxic chemicals reported to be associated with FCMs could be picked up at a level of 0.01 mg kg^-1 or lower. Overall, this review shows that the Ames test in its present form cannot be used as standalone method for evaluating the genotoxic potential of FCM migrates, but must be used together with other information from analytical chemistry and FCM manufacturing.

Use of bioassays to assess hazard of food contact material extracts: State of the art

This review focuses on the use of in vitro bioassays for the hazard assessment of food contact materials (FCM) as a relevant strategy, in complement to analytical methods. FCM may transfer constituents to foods, not always detected by analytical chemistry, resulting in low but measurable human exposures. Testing FCM extracts with bioassays represents the biological response of a combination of substances, able to be released from the finished materials. Furthermore, this approach is particularly useful regarding the current risk assessment challenges with unpredicted/unidentified non-intentionally added substances (NIAS) that can be leached from the FCM in the food. Bioassays applied to assess hazard of different FCM types are described for, to date, the toxicological endpoints able to be expressed at low levels; cytotoxicity, genotoxicity and endocrine disruption potential. The bioassay strengths and relative key points needed to correctly use and improve the performance of bioassays for an additional FCM risk assessment is developed. This review compiles studies showing that combining both chemical and toxicological analyses presents a very promising and pragmatic tool for identifying new undesirable NIAS (not predicted) which can represent a great part of the migrating substances and/or "cocktail effect".

Are styrene oligomers in coastal sediments of an industrial area aryl hydrocarbon-receptor agonists?

Effect-directed analysis (EDA) was performed to identify the major aryl hydrocarbon receptor (AhR) agonists in sediments collected from a highly industrialized area (Lake Shihwa, Korea). Great AhR-mediated potencies were found in fractions containing aromatic compounds with log Kow values of 5-8, and relatively great concentrations of styrene oligomers (SOs) and polycyclic aromatic hydrocarbons (PAHs) were detected in those fractions. Until now, there was little information on occurrences and toxic relative potencies (RePs) of SOs in coastal environments. In the present study; i) distributions and compositions, ii) AhR binding affinities, and iii) contributions of SOs to total AhR-mediated potencies were determined in coastal sediments. Elevated concentrations of 10 SOs were detected in sediments of inland creeks ranging from 61 to 740 ng g(-1) dry mass (dm), while lesser concentrations were found in inner (mean = 33 ng g(-1) dm) and outer regions (mean = 25 ng g(-1) dm) of the lake. Concentrations of PAHs in sediments were comparable to those of SOs. 2,4-diphenyl-1-butene (SD3) was the predominant SO analogue in sediments. SOs and PAHs were accumulated in sediments near sources, and could not be transported to remote regions due to their hydrophobicity. RePs of 3 SOs could be derived, which were 1000- to 10,000-fold less than that of one representative potent AhR active PAH, benzo[a]pyrene. Although concentrations of SOs in sediments were comparable to those of PAHs, the collective contribution of SOs to total AhR-mediated potencies were rather small (<1%), primarily due to their smaller RePs. Overall, the present study provides information on distributions and AhR binding affinities for SOs as baseline data for degradation products of polystyrene plastic in the coastal environment.

Qualitative impact of salinity, UV radiation and turbulence on leaching of organic plastic additives from four common plastics - A lab experiment

Four common consumer plastic samples (polyethylene, polystyrene, polyethylene terephthalate, polyvinylchloride) were studied to investigate the impact of physical parameters such as turbulence, salinity and UV irradiance on leaching behavior of selected plastic components. Polymers were exposed to two different salinities (i.e. 0 and 35 g/kg), UV radiation and turbulence. Additives (e.g. bisphenol A, phthalates, citrates, and Irgafos® 168 phosphate) and oligomers were detected in initial plastics and aqueous extracts. Identification and quantification was performed by GC-FID/MS. Bisphenol A and citrate based additives are leached easier compared to phthalates. The print highly contributed to the chemical burden of the analyzed polyethylene bag. The study underlines a positive relationship between turbulence and magnitude of leaching. Salinity had a minor impact that differs for each analyte. Global annual release of additives from assessed plastics into marine environments is estimated to be between 35 and 917 tons, of which most are derived from plasticized polyvinylchloride.