Direct Evidence for the Carrier Effect of Nanoplastics in Plants via <i>In Situ</i> Mass Spectrometry Imaging

To provide the direct evidence for comigration of plastic particles and additives in organisms, for the first time, matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) was employed to obtain in situ imaging characterization of the migration behaviors of nanoplastics (NPs) and additives in potted cactus stems. When polystyrene nanoplastics (PS-NPs) loaded with the antioxidant tris(2,4-di- tert -butylphenyl) phosphite (AO168) and flame retardant diphenyl phosphate (DPhP) were continuously exposed directly to the pith for 7 days, the additives comigrated with PS-NPs upward along stems. On the low cross-section, concentrations of PS, AO168 and DPhP were 84.8 ± 7.3, 1.5 ± 0.1, and 7.1 ± 1.9 μg/cm 2, respectively; the corresponding values on the high cross-section were 7.4 ± 0.8, 1.4 ± 0.1 and 3.8 ± 0.2 μg/cm 2 . In contrast, AO168 and DPhP were undetectable in high cross sections of the PS-NPs-free control under identical exposure levels. The mapping degrees of additives to PS-NPs decline from 63.1% at low cross-section to 1.0% at high cross-section, indicating progressive dissociation during translocation. In vitro experiments demonstrated that PS loading can significantly reduce the degradation efficiency of additives within the cactus bleeding sap. The PS-NPs entering the stems exert a carrier effect, thereby facilitating the long-distance translocation of additives to distal plant tissues.