Oral Presentation Society of Environmental Toxicology and Chemistry Australasia 2023

Weathering indices for polypropylene, polyethylene, and polystyrene microplastic samples by Pyrolysis Gas Chromatography Mass Spectroscopy (#99)

Tania TA Toapanta 1 , Elvis Dartey Okoffo 1 , Stacey O'Brien 1 , Stephen Burrows 1 , Michael Gallen 1 , Sarah Ede 2 , John Colwell 3 , Andrew Whittaker 4 , Sarit Kaserzon 1 , Kevin Thomas 1
  1. Queensland Alliance for Environmental Health Sciences, Dutton Park, QUEENSLAND, Australia
  2. School of Chemistry and Physics, Queensland University of Technology (QUT), Brisbane , Queensland, Australia
  3. School of Chemical Engineering Faculty of Engineering, Architecture and Information Technology, University of Queensland , Brisbane, Queensland , Australia
  4. Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane , Queensland, Australia

Plastics entering the marine environment can degrade into smaller pieces predomintaly through UV-irradiation and mechanical forces, such as wave action and abrasion with sediment. These pieces or weathered microplastics possess characteristic properties different from their virgin counterparts and their environmental concentrations and fate are still not well understood by using novel techniques such as Pyr-GC/MS. The simulated photooxidation conditions can potentially influence quantitative measurements using Pyr-GC/MS, while the technique can be used to identify weathering markers (oxidation products). The aim of this study was to examine whether photo-oxidation may affect quantitative measurements using a double shot Pyr-GC/MS method, as well as identify weathering markers (oxidation products) to develop a weathering index using Pyr-GC/MS.

Environmental degradation of microplastics was replicated under simulated sunlight (0.68 W/m2). Micro-sized polypropylene, polyethylene and polystyrene of two different forms; beads (size: ~5 mm; shape: oval) and fragments (size: 250-500 µm and 500-1000 µm, shape: irregular) were exposed for up to 84 days.Microplastic degradation was characterised by Pyrolysis Gas Chromatography/Mass Spectrometry (Pyr-GC/MS), Fourier-transform Infrared - Attenuated Total Reflection (FTIR-ATR), micro Fourier-transform Infrared (micro FTIR-ATR) and scanning electron microscopy (SEM).

Results showed a reduction in signal of 49% for polypropylene beads and 42% for polypropylene fragments (after 80 and 37 days, respectively) when analysed by Pyr-GC/MS. We also obtained 5 weathering markers using a low temperature method. This study suggests that under harsh weathering conditions (absence of shade, high temperature and humidity) the plastics are sufficiently oxidised to affect the quantitation of polypropylene microplastics by Pyr-GC/MS and highlights the need for further marine simulation studies and analytical comparisons between virgin and weathered microplastics in order to avoid an underestimation of microplastic in environmental samples.