Effects of TiO2, SiO2, Ag and CdTe/CdS quantum dots nanoparticles on toxicity of cadmium towards Chlamydomonas reinhardtii

Nanoparticles (NPs) are inevitably released into the aquatic environment for being widely used and may affect the toxicity of other contaminants already present in the environment, such as trace metals. However, the effects of NPs on the ecotoxicity of cadmium (Cd), a common environmental trace metal pollutant, are not well explored. In this study, effects of four widely used NPs TiO2 (n-TiO2), SiO2 (n-SiO2), Ag (n-Ag) and CdTe/CdS core/shell quantum dots (QD) on the toxicity of Cd to the freshwater algae Chlamydomonas reinhardtii were assessed respectively. Cd reduced the algae biomass, impaired the photosynthetic activities, and led to intracellular oxidative stress of algae. At non-toxic concentrations, both n-TiO2 (100 mg L-1) and n-SiO2 (400 mg L-1) attenuated the toxicity of Cd towards the algae for reducing the intracellular Cd contents, and the former was more pronounced. QD (0.5 mg L-1) increased the toxicity of Cd to algae, but n-Ag (0.2 mg L-1) had no significant influence on the Cd toxicity to algae. The microscopic observations on the ultrastructure of algae cells presented the same phenomena and n-TiO2, n-SiO2 aggregations were clearly observed outside the cell wall. Furthermore, the regulation of NPs to the Cd toxicity towards algae was related to the intracellular nitric oxide (NO), an important signaling molecule, rather than the phototaxis of algae. Above all, this study provided a basic understanding about the difference in joint toxicity of different kinds of NPs and Cd to aquatic organisms.