Uptake and translocation of nano/microplastics by rice seedlings: Evidence from a hydroponic experiment

Microplastics (MPs) are emerging contaminants in terrestrial systems that cause diverse impacts on plants. However, little is known about whether MPs especially micro-sized MPs can be accumulated and translocated in plants particularly food crops. Hereby, a hydroponic experiment was conducted to verify whether nano-sized (80 nm) and micro-sized (1 µm) fluorescently labeled polystyrene (PS) microspheres can enter rice roots and translocate to aerial parts. Plant samples were taken for detection of PS after 14 days and 40 days exposure, respectively. Both nano- and micro-sized PS microspheres were detected in roots, stems, and leaves of rice seedlings by using confocal laser scanning microscopy. Both 80 nm and 1 µm PS microspheres accumulated in the vascular systems of plant tissues, especially root stele, stem vascular bundles and leaf veins, and mostly aggregated on cell walls and in the intercellular regions. These findings imply that both nano- and micro-sized MPs could be absorbed by rice roots and subsequently translocated to aerial parts, and apoplastic transport may be the main pathway. In conclusion, rice seedlings can accumulate nano/microplastics in their roots and translocate them to aboveground tissues, thereby possibly transferring the accumulated nano/microplastics to higher trophic levels through the food chain.