The influence of dissolved and surface-bound humic acid on the toxicity of TiO₂ nanoparticles to Chlorella sp

Water Res. 2012 Sep 15;46(14):4477-87. doi: 10.1016/j.watres.2012.05.035. Epub 2012 May 31.

Abstract

NOM is likely to coat TiO₂ nanoparticles (nano-TiO₂) discharged into the aquatic environment and influence the nanotoxicity to aquatic organisms, which however has not been well investigated. This study explored the influence of nanoparticle surface-bound humic acid (HA, as a model NOM) as well as dissolved HA on the toxicity of nano-TiO₂ to Chlorella sp., with a specific focus on adhesion of the nanoparticles to the algae. Results showed that nano-TiO₂ and the dissolved HA could inhibit the algal growth with an IC₅₀ of 4.9 and 8.4 mg L⁻¹, respectively, while both dissolved and nanoparticle surface-bound HA could significantly alleviate the algal toxicity of nano-TiO₂. IC₅₀ of nano-TiO₂ increased to 18 mg L⁻¹ in the presence of 5 mg L⁻¹ of the dissolved HA and to 48 mg L⁻¹ as the result of surface-saturation by HA. Co-precipitation experiment and transmission electron microscopy observation revealed that both dissolved and nanoparticle surface-bound HA prevented the adhesion of nano-TiO₂ to the algal cells due to the increased electrosteric repulsion. The generation of intracellular reactive oxygen species (ROS) was significantly limited by the dissolved and nanoparticle surface-bound HA. The prevention of adhesion and inhibition of ROS generation could account for the HA-mitigated nanotoxicity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adsorption / drug effects
  • Cell Aggregation / drug effects
  • Chemical Precipitation / drug effects
  • Chlorella / cytology
  • Chlorella / drug effects*
  • Chlorella / growth & development
  • Chlorella / ultrastructure
  • Humic Substances / analysis*
  • Intracellular Space / chemistry
  • Malondialdehyde / metabolism
  • Nanoparticles / toxicity*
  • Nanoparticles / ultrastructure
  • Reactive Oxygen Species / metabolism
  • Solubility
  • Spectroscopy, Fourier Transform Infrared
  • Surface Properties
  • Temperature
  • Titanium / toxicity*
  • Toxicity Tests / methods*
  • X-Ray Diffraction

Substances

  • Humic Substances
  • Reactive Oxygen Species
  • titanium dioxide
  • Malondialdehyde
  • Titanium