Metabolomics reveals that engineered nanomaterial exposure in soil alters both soil rhizosphere metabolite profiles and maize metabolic pathways

Accurate risk assessment of engineered nanomaterials (ENMs) in the environment is important for sustainable development and application of nanotechnology. Soil metabolomics, which reflects the integrated response of both plant and microbial communities to ENM exposure, has not been used extensively. Moreover, since microbe-and plant-released metabolites contribute to the formation and accumulation of soil organic carbon (SOC), soil metabolite profile alteration from impacted plant and microbial activity may change SOC pool enrichment. Here, maize plants were grown in soil amended with SiO2, TiO2, or Fe3O4 ENMs (100 mg kg(-1) soil) for four weeks. Plant and soil metabolomics were then used to investigate the global metabolic response of both the plant and soil to ENM exposure. None of the tested ENMs showed negative impacts on plant growth. However, metabolomics analysis revealed that all ENM treatments altered the leaf, root and soil metabolite profiles in an ENM-dependent manner. Fe3O4 and TiO2 ENM exposure induced stronger metabolic reprogramming in leaves, roots and soil compared to SiO2 ENMs. Interestingly, leaf tissues, which is not the organ directly exposed to ENMs, showed significant amino acid pool alteration upon exposure to ENMs. In soil, levoglucosan, linolenic acid, 4-hydroxycinnamic acid and allo-inositol were significantly increased in response to ENMs. Alteration of the soil metabolite profile indicates that ENMs changed the SOC pool. Integration of leaf, root and soil metabolomics enables a thorough characterization of plant metabolism and soil chemistry that can be a powerful tool for ENM risk assessment.