Small Molecules as Markers for Decoding Plastic-Related Information: A Focus on Polymer Composition

Although the relationship between plastics and their embedded small molecules has been previously hypothesized, direct and systematic evidence remains limited. Herein, we introduced an innovative approach to validate this relationship by screening specific small molecules as markers to decode plastic information. Given the mature techniques available for polymer identification, enabling subsequent validation, this study focused on screening polymer-specific small molecule markers. Specifically, plastic samples of various polymer types─including raw plastic pellets and postprocessed plastic products─were collected, extracted, and analyzed with a nontargeted method. Distinct polymer-based features were observed in raw plastic pellets: 21 in polyethylene (PE), 69 in polypropylene (PP), 119 in poly(ethylene terephthalate) (PET), and 14 in polystyrene (PS). Of these, 2, 28, 101, and 10 features were also detected in postprocessed plastic products of the same polymer, indicating these co-occurring features could serve as polymer-specific markers. Representative markers were identified, including Irganox 1010 transformation products in PP-based plastics, PET oligomers in PET-based plastics, and dibenzoylmethane in PS-based plastics. These markers were then used to identify the polymer type of two additional plastic bottles as PET, consistent with results obtained from pyrolysis-gas chromatography/mass spectrometry. This work provides a proof-of-concept for employing small molecule markers to decode plastic-related information.