Influence of functional groups on toxicity of carbon nanomaterials:implication for toxicological evolution during atmospheric relevantaging of soot

Abstract. It has been well recognized that black carbon is toxic for human health, while it is still controversial about the influence of functionalization on its toxicity as well as the evolution of its toxicity due to chemical aging in the atmosphere. In the current study, the oxidation potential measured by dithiothreitol (DTT) decay rate and the cytotoxicity to murine macrophage cells of different functionalized carbon nanomaterials, which were used as model sample of black carbon, were investigated for understanding the role of functionalization in the toxicity of black carbon. The DTT decay rates of special black 4A (SB4A), graphene, graphene oxide, single wall carbon nanotubes (SWCNT), SWCNT-OH and SWCNT-COOH were 45.9p3.0, 58.5p6.6, 160.7p21.7, 38.9p8.9, 57.0p7.2 and 36.7p0.2 pmol min −1  μg −1 , respectively. Epoxide was found to be mainly responsible for the largest DTT decay rate of graphene oxide compared with other materials based on comprehensive characterizations. Both carboxylation and hydroxylation showed little influence on the oxidation potential of these materials, while epoxidation contributes to the enhancement of oxidation potential. All these carbon nanomaterials were toxic to murine J774 cell line. However, oxidized carbon nanomaterials (graphene oxide, SWCNT-OH and SWCNT-COOH) showed weaker cytotoxicity to J774 cell line compared with the corresponding control sample as far as the metabolic activity was considered and stronger cytotoxicity to J774 cell line regarding to the membrane integrity and DNA incorporation. These results imply that epoxidation might enhance the oxidation potential of black carbon during transport in the atmosphere.