Plastic quantification and limitations in different soil types using large-volume pyrolysis and TD-GC-MS/MS

It is a continuing challenge to analyze plastic in soil on an environmentally relevant level given the large variety and complexity of soil composition. Improvement of methods is required to: increase sample volume to meet soil heterogeneity, and simultaneously detect and quantify different types of plastic with high accuracy and precision independent of soil properties. A new combination of large-volume pyrolysis with thermal desorption-gas chromatography-tandem mass spectrometry (TD-GC-MS/MS) was used to detect a variety of polymer types without prior clean-up in larger (>1 g) soil samples. Characteristic MS/MS profiles for PA, PBAT, PE, PET, PLA, PMMA, PP, and PS were derived from plastic pyrolysis. Specifically developed rectangular, volume-defined reference micro-particles with respective weight (PE 0.48±0.12, PET 0.50±0.10, PS 0.31±0.08 µg), which can be directly introduced into solid samples for pyrolysis, were used as internal standards. For PE quantification in soil, we suggest a mathematical correction, PE_corrected, when analyzed without clean-up to account for organic matter contribution. In soil with organic carbon >1.5%, PE detection would require removal of organic matter. With a standard addition method, we quantified PS, PET and PE_corrected in complete soil matrices. To evaluate the reproducibility of plastic quantification for soils with different properties, sandy, clayey, oxide-rich and soils rich in organic matter were tested. We can now give recommendations for a simplified, more time-efficient quantification of various plastic types in a range of soil matrices and, hence, provide a robust base for future studies on the fate and effect of plastic in the environment.