Effects of Cr6+ On the Activities of Antioxidant Enzymes of Cyperus Alternifolius and Coix Aquatica Roxb Grown in Constructed Wetland.

Constructed wetlands are well received for treatment of municipal sewage in rural area. Hexavalent chromium (Cr⁶⁺) has been increasingly reported in rural domestic sewage. The effects of Cr⁶⁺ on the activities of antioxidant enzymes of plants grown in constructed wetlands are not fully understood. In this study, different concentrations of Cr⁶⁺(0, 10, 20 and 40mg/L) were spiked to domestic wastewater and the effects of Cr⁶⁺ on some physiological index and the accumulation of Cr in two plants (Cyperus alternifolius and Coix aquatica Roxb) were evaluated with a simulating vertical flow constructed wetland. A significant increase in soluble sugar(SP) contents was found in Coix aquatica Roxb leaves as compare to those of the control at 10 and 20 mg/L Cr⁶⁺, whereas the SP of Cyperus alternifolius tend to decrease at 10 to 40 mg/L Cr⁶⁺ treatment. The malondialdehyde (MDA) content significantly increased in the leaves of Cyperus alternifolius but unchanged in Coix aquatica Roxb with the treatment of 10 to 40 mg/L Cr⁶⁺ at both the seedling and tillering stage. The superoxide dismutase (SOD) activity was significantly lower in Cyperus alternifolius leaves but higher in Coix aquatica Roxb leaves at 20 and 40 mg/L Cr⁶⁺ as compared to the control at the seedling and tillering stage. Treatment of Cr⁶⁺ at 10-40 mg/L significantly enhanced the peroxidase (POD) activity in Coix aquatica Roxb leaves during the entire trial period, but such promoting effect occurred only at the tillering stage at 40 mg/L for Cyperus alternifolius. Total Cr in roots, stems and leaves was significantly higher for Cyperus alternifolius than Coix aquatica Roxb with 20 and 40 mg/L Cr⁶⁺ exposure. These results indicate that Cyperus alternifolius being more susceptible to Cr⁶⁺ exposure than Coix aquatica Roxb is related to its more sensitive antioxidant enzymes system and higher accumulation of Cr in plant.

Key words:  Aquatic plants, Antioxidant enzymes; Cr⁶⁺; wastewater treatment.