Accumulation, speciation and uptake pathway of ZnO nanoparticles in maize

Engineered nanomaterials such as ZnO nanoparticles (NPs) will inevitably enter the environment because of the large quantities produced and their widespread application. Plants comprise a fundamental living component of terrestrial ecosystems; thus, understanding the interaction between ENMs and plants is important. In the present study we conducted an integrated study by employing a combination of microscopic and spectroscopic techniques to comparatively investigate the uptake of ZnO NPs and Zn2+ ions by maize in order to further elucidate plant uptake pathways of ZnO NPs. The results demonstrate that the majority of Zn taken up was derived from Zn2+ released from ZnO NPs, and Zn accumulated in the form of Zn phosphate. ZnO NPs were observed mainly in the epidermis, a small fraction of ZnO NPs were present in the cortex and root tip cells, and some further entered the vascular system through the sites of the primary root-lateral root junction. However, no ZnO nanoparticle was observed to translocate to shoots, possibly due to the dissolution and transformation of ZnO NPs inside the plants.