Influence of pH on the Toxicity of Silver Nanoparticles in the Green Alga Chlamydomonas acidophila

The aim of this study was to investigate the effect of pH 4 and 7 on the cellular toxicity impact of silver nanoparticles (AgNPs) on the green alga Chlamydomonas acidophila. Changes in chlorophyll content, cellular viability, and reactive oxygen species (ROS) formation were determined permitting the characterization of the toxicity of AgNPs. Chemical characterization of AgNPs in suspension showed that nanoparticle size distribution was dependent to the pH of the culture medium, and a higher solubility was observed at pH 4 compared to that at pH 7. After 24 h of exposure, results indicated that the chlorophyll content and cellular viability decreased significantly, while the intracellular ROS production increased significantly, in relation to the increasing concentration of AgNPs (0.1-100 mg/L). Therefore, our results demonstrated that AgNP-induced toxicity was pH dependent as indicated by the cytotoxicity mediated through the induction of oxidative stress. In conclusion, the characterization of the physicochemical properties of AgNPs in aqueous solution having different pH is essential for the understanding of their toxicity impact on algal cells.