In an article published online on August 4, 2021, in the peer-reviewed journal Environmental Science & Technology, Charles N. Lowe from the Center for Computational Toxicology and Exposure, U.S. Environmental Protection Agency, North Carolina, US, and co-authors aimed to characterize the chemical composition of recycled compared to virgin products.
For their study, the researchers purchased 210 household articles made of virgin (56 items) or recycled materials (154) including food contact materials (FCMs), plastic children’s toys, paper products, and construction materials. They extracted the products with dichloromethane (except for 3 samples that used a 94:6 mixture of hexanes:ethyl ether) and performed nontargeted and suspect screening using gas chromatography time-of-flight mass spectrometry (GC × GC-TOF-MS). Mass spectra were compared with the National Institute of Standards and Technology 2014 Mass Spectral Library (NIST) to identify “probable structures” (the approach corresponds to a level 2 of confirmation according to Schymanski et al.). The identity of a subset of chemicals was confirmed using analytical standards (considered a level 1 identification).
A total of 918 chemical structures were tentatively identified in recycled materials and 587 in virgin materials, 112 and 110 of which were confirmed, respectively. In FCMs, a mean of 60 chemicals was identified in the recycled and 57 in virgin products. For paper products and construction materials, the number of chemicals extracted per sample was significantly higher in recycled compared to virgin products. Across all articles, 56% of the chemicals had a higher occurrence in recycled than virgin products. The analysis of functional uses of the confirmed chemicals showed that recycled products “contained greater numbers of fragrances, flame retardants, solvents, biocides, and dyes.” The scientists also performed a hierarchical cluster analysis to identify chemicals occurring in multiple products and to elucidate the potential sources of the chemicals based on chemical use information. For instance, they identified polymer additives in both virgin and recycled FCMs and associated their presence with product manufacturing. The authors highlight that this “identification of source can potentially identify candidate materials, processes, life cycle stages, or issues for targeting for chemical mitigation activities” but that more representative analyses are needed to confirm their proof of concept.
In addition, Charles and colleagues used occurrence, exposure, and bioactivity data to prioritize identified chemicals by calculating a Toxicological Priority Index (ToxPi, FPF reported) and a bioactivity-to-exposure ratio (BER). 2,4-di-tert-butylphenol (CAS 96-76-4), N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (CAS 793-24-8), 2,2′-methylenebis(4-methyl-6-tert-butylphenol) (CAS 119-47-1), 4-(1,1,3,3-tetramethylbutyl)phenol (CAS 140-66-9), and 2,4-bis(1-methyl-1-phenylethyl)-phenol (CAS 2772-45-4) had the highest ToxPi scores; the first four also being identified as “priority hazardous substances” and/or “substance of potential concern” according to the Food Packaging Forum’s Food Contact Chemicals database (FCCdb). In addition, 124 chemicals had a BER < 1 indicating that “it is possible that exposure may exceed bioactive dose”, meaning the dose previously shown to induce in vitro toxicity. The authors clarify that the aim of their study was “to investigate only the presence of chemicals in recycled products and develop approaches for investigating and/or attributing chemical sources.”
Previous reports have highlighted that eliminating chemicals of concern from plastic waste is essential to upscale plastic recycling (FPF reported), and rules have been put together that help to create plastic products that are more easily recyclable (FPF reported).
Another article, published online on August 6, by Ruben Demets and colleagues from the Centre for Polymer and Material Technologies (CPMT), Ghent University, Belgium, in the journal Resources, Conservation and Recycling, proposed a concept to quantify the suitability of a recycled plastic to replace a virgin one in a specific application considering mechanical properties and processability. Assessing the substitution potential of recycled plastic provides crucial information for transitioning to a circular economy. The scientists applied their developed concept to commercially available recycled polyethylene used in different applications such as films or bottles. The results demonstrated “the strong application dependency of the changes in technical quality for a given recycled plastic stream.” The authors emphasize that their proposed approach “is a step forward in the correct determination of the substitutability and consequently the proper assessment of the potential of end-of-life plastics as secondary resource.”
Lowe, C. N., et al. (2021). “Chemical Characterization of Recycled Consumer Products Using Suspect Screening Analysis.” Environmental Science & Technology. DOI: 10.1021/acs.est.1c01907
Demets, R. et al. (2021). “Addressing the complex challenge of understanding and quantifying substitutability for recycled plastics.” Resources, Conservation and Recycling. DOI: 10.1016/j.resconrec.2021.105826