Abstract:The reduction effect of heavy metal Pb²⁺, Cd²⁺, Cr⁶⁺ and V⁵⁺ in the contaminated water by Hydrilla verticillata and Myriophyllum verticillatum and the effects of these four heavy metals on the two macrophytes were studied under the experimental conditions. The results show that the reduction effect of Pb²⁺ by Hydrilla verticillata and Myriophyllum verticillatum are the highest. When the concentration of Pb²⁺ is 15 mg/L, the decrease rate reaches to 98.3% and 94.3%, respectively. Besides, the reduction effects of Cd²⁺ (5 mg/L) and Cr⁶⁺ (0.2 mg/L) by Hydrilla verticillata (96.5%, 69.2%)are higher than those by Myriophyllum verticillatum (70.2%, 26.7%). The reduction effects of V⁵⁺ by Hydrilla verticillata and Myriophyllum verticillatum are the lowest. When the concentration of V⁵⁺ is 2 mg/L, the reduction effects are only 16.7% and 19.2%, respectively. The test result indicates that the Chla content of Hydrilla verticillata and Myriophyllum verticillatum decline when the concentrations of Pb²⁺, Cd²⁺, Cr⁶⁺ and V⁵⁺increase, while the relative electrical conductivity increases. And the influence degree becomes more obvious as the cultivate time goes by. V⁵⁺ has the least influence on the physiological characters of two macrophytes, followed by Cr⁶⁺ and Cd²⁺. The Chla content and relative electrical conductivity of Myriophyllum verticillatum drops less than those of Hydrilla verticillata under Cr⁶⁺ and Cd²⁺ stress. The two macrophytes show a weak tolerance under Pb²⁺ stress. Both Hydrilla verticillata and Myriophyllum verticillatum can be recommended for removal of Pb²⁺, Cd²⁺, Cr⁶⁺ and V⁵⁺ from the contaminated water, and Hydrilla verticillata has a better removal ability of heavy metal.

Key words: heavy metal pollution; phytoremediation; Myriophyllum verticillatum; Hydrilla verticillata; tolerance