Cd2+ Toxicity to a Green Alga Chlamydomonas reinhardtii as Influenced by Its Adsorption on TiO2 Engineered Nanoparticles

In the present study, Cd(2+) adsorption on polyacrylate-coated TiO(2) engineered nanoparticles (TiO(2)-ENs) and its effect on the bioavailability as well as toxicity of Cd(2+) to a green alga Chlamydomonas reinhardtii were investigated. TiO(2)-ENs could be well dispersed in the experimental medium and their pH(pzc) is approximately 2. There was a quick adsorption of Cd(2+) on TiO(2)-ENs and a steady state was reached within 30 min. A pseudo-first order kinetics was found for the time-related changes in the amount of Cd(2+) complexed with TiO(2)-ENs. At equilibrium, Cd(2+) adsorption followed the Langmuir isotherm with the maximum binding capacity 31.9, 177.1, and 242.2 mg/g when the TiO(2)-EN concentration was 1, 10, and 100 mg/l, respectively. On the other hand, Cd(2+) toxicity was alleviated in the presence of TiO(2)-ENs. Algal growth was less suppressed in treatments with comparable total Cd(2+) concentration but more TiO(2)-ENs. However, such toxicity difference disappeared and all the data points could be fitted to a single Logistic dose-response curve when cell growth inhibition was plotted against the free Cd(2+) concentration. No detectable amount of TiO(2)-ENs was found to be associated with the algal cells. Therefore, TiO(2)-ENs could reduce the free Cd(2+) concentration in the toxicity media, which further lowered its bioavailability and toxicity to C. reinhardtii.