Evaluation of genotoxicity and biodistribution of various functionalised multiwalled carbon nanotubes in zebrafish (Danio rerio)

Carbon nanotubes (CNTs) are exploited for diverse applications in the aquatic ecosystem due to their unique properties. However, toxicity is a concern when using CNTs in an aquatic system and depends on several parameters. Therefore, we assessed the toxicity and distribution of CNTs in aquatic ecosystems using zebrafish as a model organism. The present study synthesised and characterised various functionalised multi walled carbon nanotubes (MWCNTs). The average size of various Pristine-MWCNTs, OH-MWCNTs, COOH-MWCNTs and BSA-MWCNTs were found to be 11.67 ± 2.03 mm, 17.67 ± 1.45 mm, 18.00 ± 2.65 mm and 25.33 ± 2.91 mm. In the acute toxicity study, the lethal concentration (LC 50 ) values of Pristine-MWCNTs, OH-MWCNTs, BSA-MWCNTs and COOH-MWCNTs at 96 h were found to be 265.16 mg/L, 215.63 mg/L, 202.94 mg/L and 130.00 mg/L respectively after exposure to zebrafish embryos. The acute toxicity effect of MWCNTs was increased upon functionalisation and varies with functional group attached. Developmental deformities such as egg coagulation, pericardial oedema, yolk sac oedema and unusual tail bend were observed. The genotoxicity effect of MWCNTs was assessed using the comet assay in the order of COOH-MWCNTs > BSA-MWCNTs > OH-MWCNTs > P-MWCNTs. Gene expression studies were performed using the intestine of zebrafish exposed to different functionalised MWCNTs. The real-time polymerase chain reaction (PCR) studies showed upregulation of DNA repair genes like p53, OGG1 and apoptosis regulator genes like Bcl2. Histological investigation revealed the biodistribution of MWCNTs in the intestine and gills and confirmed the indirect toxicity of MWCNTs in zebrafish. These results suggest that functionalisation to MWCNTs increases dispersion, which leads to increased teratogenicity, genotoxicity and biodistribution in aquatic organisms. Therefore, attention must be given to the toxicity of MWCNTs while used in aquatic applications.