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 0.480.12, PET 0.500.10, PS 0.310.08 g), 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, PEcorrected, 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 PEcorrected 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.