Pyr-GC-MS analysis of microplastics extracted from farmland soils

Microplastics are an emerging and persistent form of environmental contaminants, and they have been detected in a variety of environments. Most researchers have focused on microplastics in marine environments, but there are relatively fewer studies on farmland soil ecosystems. Therefore, the aim of this study was to investigate feasible and effective methods for the identification and quantification of microplastics in farmland soil using pyrolysis-gas chromatography mass spectrometry (Pyr-GC-MS). In this work, we report on the application of density flotation, filter membranes, and digestion for effective separation and preconcentration of microplastics in soil samples. Subsequently, we optimised the density separation approach according to the number of flotations and the density of the flotation solution. The results showed that flotation twice with NaCl solution and once with ZnCl2 solution achieved a high recovery rate of microplastics at the lowest cost. A recovery percentage of 77.30–94.87% was achieved. The precision of the recovery expressed as the relative standard deviation (RSD) of the peak area was 5.05% for polyethylene (PE) microplastics, 1.71% for polypropylene (PP) microplastics, and 0.78% for polystyrene (PS) microplastics. The above data indicated that the proposed method showed excellent reproducibility and high sensitivity. Among the samples, the main component was PE (60%), followed by PP (20%) and PS (20%). The average concentrations of PE, PP, and PS microplastics in the soil were 685.55, 1069.98, and 864.23 μg/g, respectively. Based on these results, we conclude that our method has the potential for application in routine analyses.