Impact of humic acid on the fate and toxicity of titanium dioxide nanoparticles in Tetrahymena pyriformis and zebrafish embryos.

The extensive usage of titanium dioxide (TiO 2 ) nanoparticles in daily usage products have increased their release into the environment. The present study has attempted to investigate the behaviour of titanium dioxide (TiO 2 ) nanoparticles in different experimental buffers in the presence of humic acid. Also, the effect of TiO 2 nanoparticles was assessed in different aquatic organisms with and without the presence of humic acid. The results demonstrate that humic acid increases the dispersion of TiO 2 nanoparticles via its adsorption on the surface of the nanoparticles, mainly due to electrostatic interactions. The maximum aggregation was observed in the zebrafish growth medium (E3 medium) even in the presence of humic acid. The intensity of TiO 2 nanoparticle sedimentation was observed in the order: E3 media > Dryl's buffer > MilliQ water. Interestingly, the ecotoxicity results for Tetrahymena pyriformis and Danio rerio showed that the presence of humic acid reduces the toxicity of TiO 2 nanoparticles.