Toxicological responses of Fe3O4 nanoparticles on Eichhornia crassipes and associated plant transportation.

This work investigated the interaction of Fe3O4 nanoparticles (NPs) with a floating water plant (Eichhornia crassipes). The effects of Fe3O4 NPs on E. crassipes physiology and root morphology as well as the migration and transformation of Fe3O4 NPs in plant were studied emphatically. Fe3O4 NPs (200 mg/L) showed significant growth inhibition on E. crassipes roots and leaves after a 21-day exposure, while dissolved Fe3+ ions and Fe3O4 bulk particles had no obvious effect on E. crassipes growth. Scanning electron microscopy showed that the roots of E. crassipes were significantly damaged, the root tips became thin and the root epidermis began to peel off after Fe3O4 NPs exposure. In addition, there was disordered cell arrangement and a destroyed elongation zone of the root tips. The physiology of E. crassipes was also affected. In particular, after exposure to Fe3O4 NPs (200 mg/L), a distinct decrease in chlorophyll content and catalase activity and an increase of malondialdehyde (MDA) content could be seen. Transmission electron microscopy and energy dispersive spectroscopy revealed that Fe3O4 NPs were present in the root epidermis, intercellular space and protoplasts, as well as in the leaf cytoplasm and chloroplasts. Vulcanization in the leaves was also found through diffraction analysis, which may be due to the small number of absorbed nanoparticles, some of which still existed in the original form in the leaves while others were reduced to FeS through interactions with plant components during translocation. These findings are helpful for better understanding the fate of NPs in aquatic plants. Moreover, it is important to evaluate the water environment safety of NPs.