A simple method for the selective quantification of polyethylene, polypropylene, and polystyrene plastic debris in soil by pyrolysis-gas chromatography/mass spectrometry

Abstract

The lack of adequate analytical methods for the quantification of plastic debris in soil challenges a better understanding of their occurrence and fate in the terrestrial environment. With this proof-of-principle study, we developed a simple and fast method for the selective quantification of the three most environmentally relevant polymers polyethylene (PE), polypropylene (PP), and polystyrene (PS) in soil using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). In order to facilitate the preparation of calibration series and to better account for the heterogeneity of soil matrix, polymers were dissolved in 1,2,4-trichlorobenzene (TCB) at 120 °C. Thereby, liquid sample aliquots from up to 4 g of solid sample became amenable to pyrolysis without further preparation. To evaluate the performance of this approach, three reference soils with 1.73–5.16 % organic carbon (Corg) were spiked at 50 and 250 μg g−1 of each polymer and extracted with TCB. A prior cleanup step with methanol, flocculation with KAl(SO4)2, and Fenton digestion were tested for their suitability to reduce potentially interfering Corg. Calibration curves responded linearly (adj. R2 > 0.996) with instrumental detection limits of 1–86 ng corresponding to method detection limits of 1–86 μg g−1. The measurement repeatability was 3.2–7.2 % relative standard deviation. Recoveries of 70–128 % were achieved for plastic contents of 250 μg g−1 extracted with TCB without prior cleanup from soils with less than 2.5 % Corg. A higher Corg particularly interfered with the quantification of PE. The addition of non-target polymers (polyethylene terephthalate, polyvinyl chloride, poly(methyl methacrylate), and tire wear particles) did not interfere with the quantification of the analytes highlighting the selectivity of the method. Further research is needed to determine low plastic contents in soils exceeding 2.5 % Corg. With 1–3 h processing time per sample, our method has the potential for routine analyses and screening studies of agricultural systems to be complemented with microspectroscopic techniques for additional information on particle shapes and sizes.

Simply Applicable Method for Microplastics Determination in Environmental Samples

“…Out of these, the most common and abundant is reported to be a trimer, 2,4-dimethylhept-1-en, as the main product of PP splitting [ 28 , 30 ]. This trimer was also identified in Py-GC–MS and TED-GC–MS analyses of PP, and commonly identified thermal degradation products 2,4,6-trimethyl-1-nonene, 2,4,6,8-tetramethyl-1-undecene, and 2,4,6-trimethyl-1-nonene [ 7 , 13 , 18 , 19 , 20 ].…”

“…Destructive methods rely on thermal analytical methods, such as thermogravimetry (TGA), which measure weight loss. Gaseous products may then be analyzed with thermal desorption gas chromatography mass spectrometry (TED-GC–MS) [ 7 , 8 ]; or pyrolysis followed by identification of MPs’ degradation products employing gas chromatography–mass spectrometry (Py-GC–MS) [ 9 , 10 , 11 , 12 , 13 ]. Identification of MPs using destructive methods has been widely exploited for the identification of PET, PS, PVC, PP, and PE.…”

“…Dominated PS thermal decomposition mechanisms are thought to be random and chain-end scissions, followed by depolymerization, intramolecular transfer and bimolecular termination, which lead to the formation of styrene and its larger units (dimers, trimers), aromatics, light hydrocarbons, and some oligomeric fragments [ 8 , 14 , 17 , 18 ]. The main degradation products of TED-GC–MS and Py-GC–MS analyses were identified as styrene, 2,4-diphenyl-1-buten (dimer), and 5-hexene-1,3,5-triyltribenzene, 2,4,6-triphenyl-1-hexene (trimers) [ 7 , 8 , 13 , 18 , 19 , 20 ].…”

Microwave‐Assisted Extraction for Quantification of Microplastics Using Pyrolysis–Gas Chromatography/Mass Spectrometry

“…One of these techniques is pyrolysis coupled to gas chromatography with mass spectrometry (Py–GC/MS; Dehaut et al, 2020). The Py–GC/MS technique was first used in this field for single particle characterization (Doyen et al, 2019; Fries et al, 2013; Hendrickson et al, 2018; Nuelle et al, 2014), similar to spectroscopy; however, it has been rapidly developed for whole sample mass quantification (Fischer & Scholz‐Böttcher, 2017), with a growing interest over the past few years (Funck et al, 2020; Gomiero et al, 2019; Okoffo et al, 2020; Steinmetz et al, 2020).…”

Consistent modelling of material weight loss and gas release due to pyrolysis and conducting benchmark tests of the model—A case for glovebox panel materials such as polymethyl methacrylate

“…The Py-GC-MS is an effective method for quantifying plastic materials and their decomposition products, and has been used in many studies [ 15 – 17 ]. Tubular furnaces have been also used as pyrolizers to support the quantifications [ 18 ]. The tests up to this point have made it possible to consistently evaluate the weight loss and amount of gas released from changes in the temperature of the PMMA or PC.…”