Short term exposure to multi-walled carbon nanotubes induce oxidative stress and DNA damage in Xenopus laevis tadpoles

The potential impact of Multiwalled Carbon NanoTubes (MWCNTs) was investigated on Xenopus laevis tadpoles exposed to 0.1, 1 and 10 mg/L. Oxidative stress was measured in entire larvae exposed and DNA damage (Comet assay) was carried out in erythrocytes of circulating blood from 2 h to 24 h according to standardized recommendations. Results showed significant H2O2 production when larvae were exposed to 1 mg/L and 10 mg/L of MWCNTs after 4 h and 2 h of exposure, respectively. Antioxidant enzyme activities showed significant induction of catalase (CAT), glutathione reductase (GR) and superoxide dismutase (SOD) from only 2 h of exposure to 10 mg/L of MWCNTs. In presence of 1 mg/L of MWCNTs, only GR and CAT activities were significantly induced at 4 h. Enzyme activities do not follow a simple dose-effect relation, but the time of induction is shortened in relation with the tested concentration. The Comet assay results showed significant DNA damages with a dose dependent response. The profiles of DNA damages show fluctuations, in course of time, which are characteristics of oxidative stress response in relation with the continuous balance between damage and compensation process.