Science & Technology
; Life Sciences & Biomedicine
Environmental Sciences & Ecology
The effects of single Cd(2+) and Pb(2+), and combined Cd(2+) and Pb(2+) on dehydrogenase activity and polysaccharide content of the substrate biofilms in the integrated vertical-flow constructed wetland (IVCW) were studied. Dehydrogenase activities decreased linearly with the increasing concentrations of Cd(2+) and Pb(2+) at different times (6, 24, 72, and 120 h). The activities at both 6 and 24 h were significantly higher than that at 72 and 120 h in the case of single and combined treatments. The single Cd(2+) and Pb(2+) treatments significantly inhibited dehydrogenase activities at concentrations in excess of 20 mu mol/L Cd(2+) and 80 mu mol/L Pb(2+), respectively. The inhibitory effect of Cd(2+) was much greater than that of Pb(2+). At the same time, the combined treatment of Cd(2+) and Pb(2+) Significantly inhibited dehydrogenase activities at all five concentrations studied and the lowest combined concentration was 1.25 mu mol/L Cd(2+) and 5 mu mol/L Pb(2+). A synergistic effect of Cd(2+) and Pb(2+) was observed. On the other hand, polysaccharide contents varied unpredictably with the increasing concentrations of Cd(2+) and Pb(2+) and extended experimental time. There were no significant statistical differences within the range of concentration and time studied, whether singly or in combination. These results implied that the effects of heavy metals on biofilms should be a concern for the operation and maintenance of constructed wetlands.