Humic Acid Acts as a Natural Antidote of Graphene by Regulating Nanomaterial Translocation and Metabolic Fluxes in Vivo

Abstract

Graphene-related research has intensified rapidly in a wide range of disciplines, but few studies have examined ecosystem risks, particularly phytotoxicity. This study revealed that graphene significantly inhibits the number of wheat roots and the biosynthesis of chlorophyll, and altered the morphology of shoots. Humic acid (HA), a ubiquitous form of natural organic matter, significantly (P < 0.05) relieved this phytotoxicity and recovered the sharp morphology of shoot tips. Both graphene and graphene-HA were transferred from wheat roots to shoots and were found in the cytoplasms and chloroplasts. HA increased the disordered structure and surface negative charges, and reduced the aggregation of graphene. HA enhanced the storage of graphene in vacuoles, potentially indicating an effective detoxification path. The content of cadaverine, alkane, glyconic acid, and aconitic acid was up-regulated by graphene, greatly contributing to the observed phytotoxicity. Conversely, inositol, phenylalanine, phthalic acid, and octadecanoic acid were up-regulated by graphene-HA. The metabolic pathway analysis revealed that the direction of metabolic fluxes governed nanotoxicity. This work presents the innovative concept that HA acts as a natural antidote of graphene by regulating its translocation and metabolic fluxes in vivo. This knowledge is critical for avoiding the overestimation of nanomaterial risks and can be used to control nanomaterial contamination.

Toxic effects of graphene on the growth and nutritional levels of wheat (Triticum aestivum L.): short- and long-term exposure studies

“…As an emergent nanomaterial, although the related applications of graphene are rapidly increasing, the current or future concentrations of graphene in the environment have not been determined. Hence, to be comparable with the doses of graphene used in previous phytotoxicity studies [7,8] and combined according to the US EPA toxicity studies on the food crops which commonly carried out at high concentrations (2000-5000 mg L −1 ) of the nanoparticles [14,15], the exposed graphene was prepared at 0-1500 mg L −1 in present study.…”

“…Begum [7] suggested the negative effects of graphene, wherein the growth of leaves of cabbage, tomato, and red spinach plants was inhibited after 20 days of treatment with 500-2000 mg L −1 graphene. Decreasing the concentration of graphene (200 mg L −1 ) for 5 days did not have significant adverse effects on seed germination, root length, or fresh weight of wheat plants [8]. Wang [9] and Zhao [10] showed that GO exposure in the g L −1 range for 8 days did not alter germination, seed development, or shoot and root growth in Arabidopsis plants.…”

“…In particular, information on the impact of graphene materials on plants, the key components of ecological systems, remains scarce. To date, to our knowledge, only five studies have attempted to determine the interactions of graphene materials (graphene and graphene oxide (GO)) with green plants [7][8][9][10][11]. Begum [7] suggested the negative effects of graphene, wherein the growth of leaves of cabbage, tomato, and red spinach plants was inhibited after 20 days of treatment with 500-2000 mg L −1 graphene.…”

Effect of Different Nanoparticles on Seed Germination and Seedling Growth in Rice

“…Meanwhile more investigations reported that nanopaticles had no effect on germination but did influence the growth of plants. For example, graphene had no obvious effects on wheat seed germination, whereas decreaseed the number of wheat roots [9]. CuO nanoparticles have no effects on maize seeds germination, while inhinited the root elongation [10].…”

Effects of humic acid and ionic strength on TiO2 nanoparticles sublethal toxicity to zebrafish

“…Previous research report the influence of humic acid (HA) on toxicity of TiO 2 NPs toward developing zebrafish, indicating that adsorption of HA increased suspensions stability and decreased TiO 2 NPs exposure, and TiO 2 NPs showed higher toxicity in the presence of HA (Yang et al 2013). Moreover, it has been proved that HA can increase the surface negative charges and reduce the aggregation of graphene, and then regulate (Hu et al 2014). Besides, media ionic strength yields visible toxicity of gold nanoparticles to embryonic zebrafish, suggesting that low ionic media induce morbidity and mortality but high ionic media hardly cause biological response (Truong et al 2012).…”