Chemical characterisation of the extractable organic components of agricultural plastic mulch films and their environmental fate

Abstract

Plastic mulch films are used globally in agriculture to enhance crop growth, with conventional films primarily composed of low-density polyethylene (LDPE) and biodegradable alternatives comprising polyesters like polylactic acid (PLA) and polybutylene adipate-co-terephthalate (PBAT). Plastic mulch films contain various chemical additives to enhance material properties, alongside transformation products termed non-intentionally added substances (NIASs). Direct film application to soils introduces anthropogenic chemicals into agroecosystems, some of which may pose environmental risks, yet many remain unregulated or poorly characterised. This thesis develops non-target screening (NTS) methodologies to characterise the organic chemical composition of LDPE and PLA/PBAT mulch films, assesses chemical release behaviour in leaching studies, and investigates selected additive degradation in agricultural soils.
Optimised solvent extraction and gas chromatography-mass spectrometry (GC-MS) analyses for LDPE established that hindered phenol and organophosphite triester antioxidants (11%), fatty acid amide and ethoxylated alkyl amine slip agents (50%) and n-alkane (4%) contribute most to the overall extract content, alongside uncharacterised components (30%). For PLA/PBAT film, NTS combining multiple analytical techniques revealed a complex oligoester composition. Dissolution-precipitation extracts screened with GC and GC-MS characterised 8 cyclic oligoesters up to dimers with cumulative concentrations of 2,905 ± 16.1 μg g−1 mulch film, and complimentary analysis with direct-infusion (DI)-Orbitrap-MS and high-performance liquid chromatography (HPLC)-Orbitrap-MS, identified an additional 83 oligoester components. Oligoester concentrations were comparable to the primary plasticiser content acetyltributyl citrate (ATBC; 4210 ± 135 μg g−1), emphasising oligoesters as key mulch film components.
Leaching experiments found rapid initial release of additives within seven days, with LDPE leachate dominated by surface-active lubricants and PLA/PBAT films releasing oligoesters and plasticisers that reflected the solvent extract composition. Biodegradable films released only ~4% of their solvent-extracted content over 21 days, warranting long-term leaching investigations. Soil degradation studies of 10 priority additives revealed disparities in degradation dynamics, and robust data for tested phthalate plasticisers suggested that degradation was unchanged between mixed and individual additive incorporation at the tested concentrations (500 ng g−1 soil per analyte). However, due to the varying chemistries of the additives investigated and interference from contaminants, conclusive results could not be obtained for all analytes, necessitating future optimisation of the methodology.
These findings advance understanding of plastic mulch film chemistry, demonstrating the need for holistic analytical approaches to assess the material’s organic composition. Furthermore, this thesis contributes knowledge to the environmental risk assessment of plastic mulch films, which seeks to ensure cultivational benefits are not accompanied with significant detrimental chemical effects to agroecosystem functioning.

Date of Award	9 Dec 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Michaela Reay (Supervisor), Charlotte E M Lloyd (Supervisor) & Richard P Evershed (Supervisor)