Foliar uptake and in-leaf translocation of micro(nano)plastics and their interaction with epicuticular wax

Abstract

The pollution of micro(nano)plastics (MNPs) in agroecosystems is of increasing concern for its negative impact on living organisms. However, the information on how MNP size and leaf characteristics influence the bioaccumulation, cellular localization and translocation of MNPs in crop leaves is seriously lacking. Here, soil-grown maize and soybean plants were foliar exposed to nano-sized (80 nm) and micro-sized (500 nm) polystyrene (PS) MNPs. Smaller size and trichomes favored higher accumulation of PS MNPs on the crop leaf surfaces. Regardless of crop species, 500 nm PS remained mainly on the leaf epidermis with little present in the apoplast or cytoplasm. 80 nm PS migrated to the maize leaf interior via stomatal and cuticular pathways, while their penetration into the soybean leaves was observed via a single cuticular pathway due to the presence of trichomes. Subsequently, 80 nm PS appeared within the apoplast and in the cytoplasm, and penetrated deeper into the vasculature via apoplastic and symplastic pathways. The interaction of 80 nm PS with n-alkanes and esters demonstrated that the deposition of 80 nm PS on the leaves induced a remarkable ‘wax degradation’, i.e., a phase transition of wax ultrastructure from crystalline to amorphous structures. These findings provide a scientific basis for in-depth understanding of the environmental behaviors and physiological effects of MNPs in air–vegetation systems, which are valuable for assessing their potential risks to food safety.