Lethal and Sublethal Toxicity of Nanosilver Carbon Nanotubes Composites to Hydra vulgaris- a Toxicogenomic Approach

The increasing use of nanocomposites as raised concerns about the potential environmental impacts are less understood than those obtained with individual nanomaterials. The purpose of this study was to investigate the lethal and sublethal toxicity of nano-silver carbon walled nanotubes (nAg-CWNT) composites in Hydra vulgaris. The lethal and sublethal toxicity was determined based on the characteristic morphological changes (retraction/loss of tentacles and body disintegration) for this organism. In addition, a qPCR array was optimized and involved gene expression for oxidative stress (superoxide dismutase, catalase), regeneration and growth (serum response factor), protein synthesis, oxidized DNA repair, neural activity (dopamine decarboxylase) and the proteasome/autophagy pathways. The hydras were exposed for 96 h to increasing concentration of single nAg, CWNT and to 10% nAg-90% CWNT and 50% nAg-50% CNWT composites. Transmission microscopy and X-ray fluorescence analysis revealed the presence of nAg attached to the carbon nanotubes and nAg aggregates. The data revealed that the nAg-CWNT composites were more toxic than their counterparts (nAg and CNWT). The sublethal morphological changes (EC50) were strongly associated with oxidative stress and protein synthesis while lethal morphological changes (LC50) encompassed changes in dopamine activity, regeneration and proteasome/autophagic pathways. In conclusion, the toxicity of nAg-CWNT composites presents a different pattern in gene expression and at lower threshold concentrations than those obtained for nAg or CWNT alone.