In an article published on November 4, 2023, in the journal Recycling, Elisa Mayrhofer from the Austrian Research Institute for Chemistry and Technology (OFI), Vienna, and co-authors assessed if DNA-reactive, mutagenic substances are present in recycled polyolefins compared to polyethylene terephthalate (PET) and polystyrene (PS), using the cell-based Ames in vitro assay.
Currently, the European Food Safety Authority (EFSA) assumes that all unidentified contaminants in recycled plastics are DNA-reactive and mutagenic, and prescribes an exposure limit of 0.0025 µg/kg body weight per day for each of them. Therefore, the authors aimed to assess if that assumption is justified and if the combination of the Ames test with chromatographic analysis allows the detection of these unknown substances.
While EFSA has almost exclusively assessed the safety of PET recycling processes for food contact uses, the European regulation on recycled plastics in food contact, (EU) 2022/1616, now allows novel non-authorized technologies on the market while necessary data for their safety are being collected, prior to safety assessments being carried out (FPF reported and here). Therefore, a toxicological and chemical characterization of polymers other than PET is key.
For their analysis, Mayrhofer and colleagues acquired a total of 119 recycled plastic samples from their industry partners, focusing on polyolefins, specifically low-density polyethylene (LDPE, 14 samples), high-density polyethylene (HDPE, 40), and polypropylene (PP, 37) but also including 10 PS and 12 PET samples for comparison. The samples can be further differentiated into washed flakes from post-consumer waste (input) and recycled granules or finished products made from these (output). Samples were extracted with 95% ethanol at 60°C for one to ten days and pre-concentrated extracts were applied to a miniaturized Ames test to detect DNA-reactive, mutagenic substances.
The researchers detected DNA-reactive, mutagenic substances in 51 of the 119 recycled samples. However, since the sensitivity of the miniaturized Ames test does not allow the detection of substances at the levels of EFSA’s safety threshold (0.0025 µg/kg body weight per day), “additional DNA-reactive, mutagenic effects [of investigated samples] cannot be ruled out.”
The positive samples included all plastic types except for recycled PET which is already widely applied for food contact in Europe. According to the authors, the different polymer structure of polyolefins, where compounds are more easily transferred into the solvent, is one reason for the higher chemical migration compared to PET. Further, six out of the ten PS samples showed reactivity. Previous studies on post-consumer and recycled plastic polymers came to the same conclusion that PET is currently the only polymer that complies with EFSA’s requirements for plastics in a circular economy (FPF reported). However, technical and physical constraints in mechanical recycling also prevent infinite recycling of PET, as revealed by a report published in November 2023 (FPF reported), and recycled food contact PET has been found to contain hazardous chemicals, like bisphenol A (FPF reported).
The comparison of input and output samples showed that DNA-reactive, mutagenic substances were more prevalent in output materials (42 positive samples out of 92) than in input materials (7 positive samples out of 27). Therefore, the authors hypothesized that harmful chemicals are not introduced by consumers but during the recycling processes and called for further characterization of these compounds and their sources. When comparing the bioassay with the analytical screening results, chemicals explaining the observed toxicity could not be identified.
Mayerhofer and co-authors consider their findings concerning and hindering “the progress in plastic recycling especially in sensitive applications such as food contact materials.”
Another article published on October 30, 2023, in the journal Data in Brief supports this conclusion considering the complex (and harmful) chemical mixtures in plastics. Eric Carmona from the University of Gothenburg, Sweden, and co-authors purchased 28 HDPE plastic pellets from recycling facilities in South America, Asia, Africa, and Europe, extracted them with three types of organic solvents using ultrasound, and applied them to gas and liquid chromatography-high resolution-mass spectrometry (GC and LC-HRMS) for targeted and non-targeted chemical screening. Thereby, targeted screenings are used to quantify levels of known (hazardous) chemicals, while non-targeted screenings serve to identify previously unknown chemicals.
The researchers detected and quantified a total of 491 chemicals by targeted analysis. Another 170 compounds were tentatively identified in the non-targeted screening. Classification of these chemicals showed that most were pesticides and biocides (162 compounds), pharmaceuticals (89), industrial chemicals (65), and plastic additives (45). The plasticizer n-ethyl-o-toluenesulfonamide (CAS 1077-56-1) was present in all samples and was the chemical with the highest concentration (up to 24020 μg/L of extract) followed by the rubber additive n,n-dimethyl-p-phenylenediamine (CAS 99-98-9; up to 77463 ng/L of the extract). The whole dataset can be found in a Zenodo repository. The authors write that the “dataset [is] advancing knowledge of the complex chemical composition associated with recycled plastics.”
Not only does the presence of toxic and complex chemical mixtures impede the progress of recycling, but also food and drink companies are not progressing toward its set goals. For instance, DW’s and European Data Journalism Network’s investigations on recycling rates of plastic recycling in Europe published in 2022 revealed that two-thirds of plastic-packaging pledges in Europe failed (FPF reported).
References
Carmona, E. et al. (2023). “A dataset of organic pollutants identified and quantified in recycled polyethylene pellets.” Data in Brief. DOI: 10.1016/j.dib.2023.109740
Mayrhofer, E. et al. (2023). “Safety Assessment of Recycled Plastics from Post-Consumer Waste with a Combination of a Miniaturized Ames Test and Chromatographic Analysis.” Recycling. DOI: 10.3390/recycling8060087
