A practical method for mass quantification of microplastics in soil media using pyrolysis gas chromatography-mass spectrometry

Microplastic (MP) contamination in soil media presents growing analytical challenges. We introduce a validated method for MP mass quantification using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), targeting polyethylene (PE), polypropylene (PP), and polystyrene (PS) in synthetic and environmental soils. The method achieved low limits of detection (0.02-0.44 µg), strong linearity (R² > 0.995), and high recovery rates-86.1% (sandy), 90.7 % (loamy), and 99.6 % (sandy-loam). Cryomilling improved sample homogeneity and quantification accuracy (+3.2 %). Fourier transform infrared spectroscopy (FTIR) was used to confirm polymer identity with >85% match. The protocol was successfully applied to environmental samples from urban and agricultural soils in Auckland, New Zealand, demonstrating its robustness and field applicability. This practical workflow offers a reproducible, high-sensitivity approach suitable for routine microplastics monitoring across diverse soil matrices. Py-GC/MS method achieved over 90 % accuracy for microplastic quantification. Extraction protocols demonstrated recovery efficiencies of up to 99.6 % FTIR complemented Py-GC/MS, confirming polymer identification with >85 % accuracy.