Foliar spraying of different size SiO2 nanoparticles affected phenanthrene accumulation in amaranth (Amaranthus tricolor L.): A metabolomics insight

Silica nanoparticles (nSiO 2 ) have attracted considerable attention in agricultural practices. However, their effects on polycyclic aromatic hydrocarbon (PAH) accumulation in plants remain largely unknown. Thus, this issue was tracked here with a 30-d pot experiment with foliar spraying different sizes of nSiO 2 (100 mg L -1 , 10 mL) on Amaranthus tricolor L. (amaranth). Results showed that 30 nm and 100 nm nSiO 2 increased phenanthrene (PHE) contents in amaranth leaves by 242% ± 88.4% and 158% ± 29.6%, respectively, which was more significant than 2 µm particles (96.0% ± 29.2%). Metabolomics indicated that compared to nSiO 2 , 2 µm SiO 2 more significantly boosted oxidative defense in amaranth leaves, enhanced cell membrane fluidity, and upregulated amino acid metabolism, glycolysis, and gluconeogenesis. In addition, the upregulation of discriminating metabolites was the most significant in 2 µm SiO 2 -treatment, followed by 100 nm and 30 nm. This is mainly because nSiO 2 promoted amaranth growth and decreased average PHE content per unit biomass, namely “dilute effect”. Thus, slighter metabolic disturbances were observed in 30 nm and 100 nm SiO 2 -treated group. The present study revealed the possibility of PAHs accumulation enhancement in vegetables with nSiO 2 foliar spayed. The results of this study provide theoretical guidance regarding to particle size selection for the safe agricultural application of nSiO 2 in PAHs-contaminated areas.