Nanoplastic and microplastic contamination in Australian carbonated beverages: Measurement by pyrolysis-GC-MS and the challenge of poly(ethylene terephthalate) oligomer interference

Bottled beverages are increasingly recognised as an important source of dietary exposure to nanoplastics (NP) and microplastics (MP), with source water speculated to contribute to contamination. This study assessed the extent to which the fingerprint of local water sources contributes to NP and MP contamination of Australian carbonated beverages, and examined the utility of the method proposed in the Draft ISO Standard: Water quality — Analysis of microplastic in water —Part 3: Thermo-analytical methods for waters with low content of suspended solids including drinking water for application to carbonated beverages. Pyrolysis-gas chromatography-mass spectrometry (Pyr-GC-MS) was used to quantify NP and MP in bottled and soda-fountain beverages manufactured in Australia. In bottled beverages, polypropylene (<MDL - 0.45 µg/L), poly(methyl methacrylate) (0.003 - 0.09 µg/L), polycarbonate (<MDL - 1.4), nylon 6 (<MDL - 1.12), and nylon 6,6 (0.11 - 7.2 µg/L) were detected across all size fractions analysed (>2.7 µm, 2.7 - 1.0 µm, and 1.0 - 0.3 µm). Polypropylene, poly(methyl methacrylate), polystyrene, nylon 6 and nylon 6,6 were also detected in soda fountain carbonated beverages. Comparison of NP and MP concentrations revealed no similarity between bottled carbonated beverages and bottled water from the same manufacturer, or between soda fountain beverages and tap water collected at the same location. Quantification of poly(ethylene terephthalate) (PET) was further assessed for accuracy due to frequent detection of high concentrations of pyrolysis products. PET oligomers (repeating units of ethylene terephthalate) were identified as an important interference for PET analysis by Pyr-GC-MS, as they form the same pyrolysis products in both single and double shot mode, providing a false positive PET detection. PET could not therefore be confidently quantified. This study provides preliminary evidence of MP and NP in store bought carbonated beverages, and also provides the first evidence of oligomer interference, further highlighting the challenges of quantifying PET in water using Pyr-GC-MS.