Toxicity of three carbon-based nanomaterials to earthworms: Effect of morphology on biomarkers, cytotoxicity, and metabolomics

Widespread use of carbon-based nanomaterials (CNs) leads to their accumulation in the terrestrial ecosystem, persistently threatening faunal biodiversity and the entire environment. However, less is known about the influence of high concentration CNs on soil biota than on atmospheric or aquatic organisms. In this study, the impacts of three CNs, carbon black (CB), reduced graphene oxide (RGO), and single-wall carbon nanotube (SWCNT) are compared on Eisenia fetida, an early warning soil invertebrate for pollution events. Observations revealed a morphology-dependent toxicity of CNs to earthworms. The aspect ratio and hydrodynamic size of CNs most likely dictated their adverse effects on the body weights, antioxidant systems, coelomocytes, and non-targeted metabolomic profiles of the worms. Multivariate regression analyses showed that the CNs with a higher aspect ratio (SWCNT followed by RGO) exerted more stress on the metabolic processes of earthworms. Cell viability and the phenylalanine to leucine ratio were distinct biomarkers that indicated the detrimental extent of the various forms of CNs. Membrane-associated metabolite choline changes indicated that the potential harm of the sharp CNs may have been due to membrane disruption. These results highly suggested that the soil environmental risk of CNs was related to their particle morphology, contributing to a comprehensive understanding of the nano-agriculture.