Quantification of nanoplastics uptake and transport in lettuce by pyrolysis gas chromatography-mass spectrometry

Nanoplastics (NPs) can enter the edible parts of crop and threaten human health, which attract widespread attention. However, the precise quantification of NPs in crop is still a tremendous challenge. Herein, a method with Tetramethylammonium hydroxide (TMAH) digestion, dichloromethane extraction combined with pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) quantification was present to quantify polystyrene (PS) NPs uptake in lettuce (Lactuca sativa). 25% of TMAH was optimized as extraction solvent and 590 °C was selected as pyrolysis temperature. Recoveries of 73.4-96.9% were obtained for PS-NPs at spiking level of 4-100 μg/g in control samples (RSD < 8.6%). The method exhibited good intra-day and inter-day reproducibility, detection limits of 34-38 ng/g and linearity with 0.998-0.999. The reliability of Py-GC/MS method was verified by europium-chelated PS using inductively coupled plasma mass spectrometry (ICP-MS). To simulate different environmental conditions, hydroponic culture and soil incubated lettuce were exposed to different concentrations of NPs. Higher levels of PS-NPs were detected in roots and very few was transferred to the shoots. NPs in lettuce were confirmed by laser scanning confocal microscopy (LSCM). The developed method provides new opportunities for the quantification of NPs in crops.