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Characterisation of the unknown chemical composition of a commercial biodegradable agricultural plastic mulch film using complementary spectrometric and spectroscopic techniques
Summary
Scientists used an array of advanced chemical analysis techniques to comprehensively characterise the additives and unintended chemical components in a commercially available biodegradable agricultural mulch film made from PLA and PBAT. They discovered not only the expected ingredients but also an unreported polyester component and 83 additional chemical species, including a plasticiser and numerous cyclic oligomers that could leach into soil. This work is important because biodegradable mulch films are promoted as a solution to plastic pollution in farmland, yet they carry their own chemical burdens that need to be fully understood before widespread adoption.
Biodegradable polyester mulch films are a viable alternative for use in agriculture to polyolefin-based films, offering reduced long-term microplastic pollution in agroecosytems with comparable protections for food security. However, these films carry diverse organic additives and non-intentionally added substances (NIASs), representing an underexplored source of anthropogenic chemicals in agroecosystems. Comprehensive chemical characterisation of these films is critical but hindered by restrictions on revealing proprietary formulations. This study presents a non-targeted screening (NTS) workflow employing multiple complementary analytical techniques to elucidate the organic composition of a polylactic acid (PLA)/polybutylene adipate-<i>co</i>-terephthalate (PBAT) mulch film. <sup>1</sup>H nuclear magnetic resonance (NMR) quantified polyester contributions to the blend and revealed an unreported polybutylene sebacate (PBSe) component, likely from polybutylene sebacate terephthalate (PBSeT). Dissolution-precipitation extraction of the film followed by gas chromatography-mass spectrometry (GC-MS) and GC-flame ionisation detection (GC-FID) identified key additives in the extracted soluble fraction, including acetyl tributyl citrate (ATBC) plasticiser (4210 ± 135 μg g<sup>-1</sup>), and 8 cyclic oligoesters up to dimers. High-performance liquid chromatography-Orbitrap-mass spectrometry (HPLC-Orbitrap-MS) and direct infusion (DI)-Orbitrap-MS expanded oligoester detection to 83 additional components beyond the analytical window of GC-MS. The detailed oligoester profiles underscore the need to apply this workflow to biodegradable mulch films from diverse commercial sources and food industry applications to assess their broader chemical variability. These methodologies offer critical tools for the life cycle assessment of biodegradable agricultural plastic mulch films, advancing our understanding of the environmental impact and safety of these new materials.
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