The influence of dissolved and surface-bound humic acid on the toxicity of TiO₂ nanoparticles to Chlorella sp.
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.
Department of Environmental Science, Zhejiang University, Hangzhou 310058, China. lindaohui@zju.edu.cn
Daohui
D
Lin
Jing
J
Ji
Zhifeng
Z
Long
Kun
K
Yang
Fengchang
F
Wu
D000327:Adsorption / Q000187:drug effects; D002449:Cell Aggregation / Q000187:drug effects; D011232:Chemical Precipitation / Q000187:drug effects; D002708:Chlorella / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D006812:Humic Substances / Q000032:analysis*; D042541:Intracellular Space / Q000737:chemistry; D008315:Malondialdehyde / Q000378:metabolism; D053758:Nanoparticles / Q000633:toxicity* / Q000648:ultrastructure; D017382:Reactive Oxygen Species / Q000378:metabolism; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013696:Temperature; D014025:Titanium / Q000633:toxicity*; D018675:Toxicity Tests / Q000379:methods*; D014961:X-Ray Diffraction
D006812:Humic Substances; D017382:Reactive Oxygen Species; C009495:titanium dioxide; D008315:Malondialdehyde; D014025:Titanium