From elements to isotopes: Fingerprinting consumer plastics.

Polymer identification alone rarely informs on additive provenance or metal interactions. We tested whether multi-element profiles and selected metal isotopes provide complementary and reproducible fingerprints of consumer plastics. We analyzed 119 items spanning major polymers and colors after microwave digestion. Forty-one elements were quantified by ICP-MS; Cu, Sr, and Pb isotope ratios were measured by MC-ICP-MS on selected purified subsets. Elemental concentrations span over eight orders of magnitude (from Rare Earth Elements (REE) at μg kg to Ca at >10 μg kg). Non-parametric statistics reveal significant polymer and color effects; polypropylene (PP) shows higher Mg, Si, Cr, and Ni concentrations than polyethylene (PE), while color modulates Cu and some REE. Strontium isotope ratios vary widely (Sr/Sr = 0.70765-0.71320), consistent with contributions from disparate mineral fillers and pigments. Copper isotopes are systematically enriched in Cu with variable values (δCu = +0.18‰ to +1.35‰), supporting the influence of distinct Cu-based pigment formulations. Lead isotope ratios further discriminate legacy Pb-bearing additives observed in a subset of items, consistent with distinct manufacturing and/or recycled streams. Overall, combined elemental-isotopic fingerprints thus provide complementary, integrated and transferable markers of additive provenance beyond spectroscopic polymer identification. These signatures open new avenues for source apportionment and understanding the fate of environmental plastics.