Cd 2+ toxicity to a green alga Chlamydomonas reinhardtii as influenced by its adsorption on TiO 2 engineered nanoparticles

Abstract

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. © 2012 Yang et al.