Abstract：Toxic effect of cadmium on Microcysis aeruginosa Kutz. and Scenedesmus obliquus (Turp.) Kutz were researched by using different concentrations of Cd2+. The results showed the growth of S. obliquus was accelerated in Cd2+ concentration of 0.1mg/L, and decreased in Cd2+ concentration over 0.15mg/L. Toxicant could promote the growth at low concentration while restrain at high concentration, which might be an effect of hormesis. But M. aeruginosa was more sensitive to Cd2+ with the growth obviously inhibited when the concentrations of Cd2+ were 0.05mg/L and treat 72h, and the inhibitory effect was obvious with increasing Cd2+. The membrane permeability of the two algae changed under the stress of Cd2+, and protein and nucleic acid contents of two freshwater algae rose up. The photos of scanning electron-microscopy showed that the superficial flocs of algae increased with the rise of Cd2+ concentration, especially for M. aeruginosa. Meanwhile, contents raised and the POD and CAT activities in the two algae all increased with the rise of Cd2+ at the early stage. The two algae could absorb Cd2+, and S. obliquus had more adsorption ability than M. aeruginosa at the unit cell. The results indicated that the main toxic mechanisms of Cd2+ imposing on two algae involved the superoxide anion radical generation that induced the physiological and biochemical changes of the algae, and hurt the algae. Compared with the M. aeruginosa, S. obliquus not only had a better tolerant of Cd2+, but a better adsorption ability of Cd2+. It indicates that S. obliquus has the potential of being a biological material to deal with water Cd2+.
