Translocation, Bioaccumulation and Environmental Effects of Graphene Materials in Plants

Abstract

Graphene is the most important and applied carbon nanomaterials nowadays. Plenty of graphene products are commercially available, including screen, battery, filter and cloth. With the increase of research, production, application and discharge of graphene based products, graphene would enter the environment and induce unwanted toxicity, which requires thorough investigations. Plants are the producer of biogeochemical cycle and provide the fundament of energy and material for the environment. In the past years, we used 13C labelled graphene as the tracer to investigate the translocation, bioaccumulation and environmental effects of graphene in plants. 13C-labled graphene oxide (GO) and reduced GO (RGO) were prepared by arc discharge method, followed by Hummer’s method and chemical reduction. 13C-labeled graphene was quantified by isotope ratio mass spectroscopy (IRMS). The results indicated that GO was restricted in the roots of plants and hardly migrated to the stem and leaves. On the other hand, RGO could translocate from roots to stems and leaves. GO was toxic to plant roots, indicated by the inhibited root elongation and the changed structure. The toxicity to root further led to the growth inhibition of whole plants. However, GO did not change the photosynthesis parameters. In contrast, RGO showed much lower toxicity to plant roots. The accumulation of RGO in leaves led to the inhibition of photosynthesis. The ultrastructure of leaves did not change upon the exposure to RGO. In addition, due to the strong interaction of GO and soil, the soil cultivation of plants alleviated the toxic effects of GO comparing to that in water cultivation. The shape and size also regulated the toxicity of GO, where hydroxylated fullerene (spherical and smaller) had no toxicity to plants and migrated easier. Further, the toxicity of GO and RGO to plants was attributed to the oxidative stress in plants.