Ecotoxicological Studies of ZnO and CdS Nanoparticles on Chlorella vulgaris Photosynthetic Microorganism in Seine River Water.

Seine river water was used as natural environmental medium to study the ecotoxicological impact of ZnO and CdS nanoparticles and Zn2+ and Cd2+ free ions using Chlorella vulgaris as a biological target. It was demonstrated by viability tests and photosynthetic activity measurements that free Zn2+ (IC50 = 2.7 x 10(-4) M) is less toxic than free Cd2+ and ZnO nanoparticles (IC50 = 1.4 x 10(-4) M). In the case of cadmium species, free Cd2+ (IC50 = 3.5 x 10(-5) M) was similar to CdS nanoparticles (CdS-1: IC50 = 1.9 x 10(-5) M and CdS-2: IC50 = 1.9 x 10(-5) M), as follows: CdS > Cd2+ > ZnO > Zn2+. Adenosine-5'-triphosphate (ATP) assay and superoxide dismutase (SOD) enzymatic activity confirmed these results. Transmission electron microscopy (TEM), coupled with energy-dispersive X-ray spectroscopy (EDS), confirmed the internalization of CdS-1 nanoparticles after 48 h of contact with Chlorella vulgaris at 10(-3) M. With a higher concentration of nanoparticles (10(-2) M), ZnO and CdS-2 were also localized inside cells.