The effects of hydroxylated multiwalled carbon nanotubes on the toxicity of nickel to Daphnia magna under different pH levels.

Hydroxylated multiwalled carbon nanotubes (OH-MWCNTs), with large amounts of hydrophilic groups attached on the nanoparticle surface, have caused considerable concern because of their inevitable release into aquatic environments. They may interact with other contaminants such as heavy metals and even influence their toxicity, fate, and transport. In the present study, the stability of OH-MWCNTs suspended in aerated Nanjing tap water (moderately hard) was evaluated using the spectrophotometric method. The toxicity of OH-MWCNTs to Daphnia magna was determined, and nontoxic concentrations were used in acute toxicity, accumulation, and sorption tests. It was found that OH-MWCNTs increased the Ni toxicity in a concentration-dependent manner under different pH levels. Nickel adsorption onto the OH-MWCNTs and the uptake of OH-MWCNTs increased the exposure of D. magna to Ni, which was verified by sorption and accumulation tests conducted under different pH levels. The lower pH level contributed to a higher overall toxicity, which could be interpreted by the increasing amount of Ni adsorption onto OH-MWCNTs with the decreasing pH levels.